Provided by: bash_4.0-5ubuntu2_i386 bug

NAME

       bash - GNU Bourne-Again SHell

SYNOPSIS

       bash [options] [file]

COPYRIGHT

       Bash is Copyright (C) 1989-2009 by the Free Software Foundation, Inc.

DESCRIPTION

       Bash  is  an  sh-compatible  command language interpreter that executes
       commands read from the standard  input  or  from  a  file.   Bash  also
       incorporates  useful features from the Korn and C shells (ksh and csh).

       Bash is intended to be a conformant implementation  of  the  Shell  and
       Utilities  portion  of  the  IEEE  POSIX  specification  (IEEE Standard
       1003.1).  Bash can be configured to be POSIX-conformant by default.

OPTIONS

       In addition to the single-character shell  options  documented  in  the
       description  of  the set builtin command, bash interprets the following
       options when it is invoked:

       -c string If the -c option is present,  then  commands  are  read  from
                 string.   If  there  are arguments after the string, they are
                 assigned to the positional parameters, starting with $0.
       -i        If the -i option is present, the shell is interactive.
       -l        Make bash act as if it had been invoked as a login shell (see
                 INVOCATION below).
       -r        If  the  -r  option  is present, the shell becomes restricted
                 (see RESTRICTED SHELL below).
       -s        If the -s option is present, or if no arguments remain  after
                 option  processing,  then commands are read from the standard
                 input.  This option allows the positional  parameters  to  be
                 set when invoking an interactive shell.
       -D        A  list of all double-quoted strings preceded by $ is printed
                 on the standard output.   These  are  the  strings  that  are
                 subject  to  language  translation when the current locale is
                 not C or POSIX.  This implies the -n option; no commands will
                 be executed.
       [-+]O [shopt_option]
                 shopt_option  is  one  of  the  shell options accepted by the
                 shopt  builtin  (see  SHELL  BUILTIN  COMMANDS  below).    If
                 shopt_option is present, -O sets the value of that option; +O
                 unsets it.  If shopt_option is not supplied,  the  names  and
                 values  of the shell options accepted by shopt are printed on
                 the standard output.  If the invocation  option  is  +O,  the
                 output  is displayed in a format that may be reused as input.
       --        A -- signals the end of options and disables  further  option
                 processing.   Any  arguments  after  the  --  are  treated as
                 filenames and arguments.  An argument of - is  equivalent  to
                 --.

       Bash  also  interprets  a  number  of  multi-character  options.  These
       options must appear on the command  line  before  the  single-character
       options to be recognized.

       --debugger
              Arrange for the debugger profile to be executed before the shell
              starts.  Turns on extended debugging mode (see  the  description
              of  the  extdebug  option  to the shopt builtin below) and shell
              function tracing (see the description of the -o functrace option
              to the set builtin below).
       --dump-po-strings
              Equivalent  to  -D,  but  the  output  is  in the GNU gettext po
              (portable object) file format.
       --dump-strings
              Equivalent to -D.
       --help Display  a  usage  message   on   standard   output   and   exit
              successfully.
       --init-file file
       --rcfile file
              Execute   commands   from   file  instead  of  the  system  wide
              initialization file /etc/bash.bashrc and the  standard  personal
              initialization  file  ~/.bashrc if the shell is interactive (see
              INVOCATION below).

       --login
              Equivalent to -l.

       --noediting
              Do not use the GNU readline library to read command  lines  when
              the shell is interactive.

       --noprofile
              Do  not read either the system-wide startup file /etc/profile or
              any  of  the  personal  initialization  files   ~/.bash_profile,
              ~/.bash_login,  or  ~/.profile.   By  default,  bash reads these
              files when it is  invoked  as  a  login  shell  (see  INVOCATION
              below).

       --norc Do  not  read  and  execute  the system wide initialization file
              /etc/bash.bashrc and the personal initialization file  ~/.bashrc
              if  the  shell  is interactive.  This option is on by default if
              the shell is invoked as sh.

       --posix
              Change the behavior of bash where the default operation  differs
              from the POSIX standard to match the standard (posix mode).

       --restricted
              The shell becomes restricted (see RESTRICTED SHELL below).

       --verbose
              Equivalent to  -v.

       --version
              Show  version  information  for  this  instance  of  bash on the
              standard output and exit successfully.

ARGUMENTS

       If arguments remain after option processing, and neither the -c nor the
       -s  option  has  been supplied, the first argument is assumed to be the
       name of a file containing shell commands.  If bash is invoked  in  this
       fashion,  $0  is  set  to  the  name  of  the  file, and the positional
       parameters are set to the remaining arguments.  Bash reads and executes
       commands  from  this  file, then exits.  Bash’s exit status is the exit
       status of the last command executed in the script.  If no commands  are
       executed,  the  exit status is 0.  An attempt is first made to open the
       file in the current directory, and, if no file is found, then the shell
       searches the directories in PATH for the script.

INVOCATION

       A  login shell is one whose first character of argument zero is a -, or
       one started with the --login option.

       An interactive shell is one started without  non-option  arguments  and
       without the -c option whose standard input and error are both connected
       to terminals (as determined by isatty(3)), or one started with  the  -i
       option.   PS1 is set and $- includes i if bash is interactive, allowing
       a shell script or a startup file to test this state.

       The following paragraphs describe how bash executes its startup  files.
       If  any  of  the files exist but cannot be read, bash reports an error.
       Tildes are expanded in  file  names  as  described  below  under  Tilde
       Expansion in the EXPANSION section.

       When  bash  is  invoked  as  an  interactive  login shell, or as a non-
       interactive shell with the --login option, it first reads and  executes
       commands  from  the  file  /etc/profile,  if  that  file exists.  After
       reading that file, it looks  for  ~/.bash_profile,  ~/.bash_login,  and
       ~/.profile,  in  that  order,  and reads and executes commands from the
       first one that exists and is readable.  The --noprofile option  may  be
       used when the shell is started to inhibit this behavior.

       When  a  login  shell  exits, bash reads and executes commands from the
       file ~/.bash_logout, if it exists.

       When an interactive shell that is not a login shell  is  started,  bash
       reads  and  executes  commands  from /etc/bash.bashrc and ~/.bashrc, if
       these files exist.  This may be inhibited by using the  --norc  option.
       The  --rcfile  file option will force bash to read and execute commands
       from file instead of /etc/bash.bashrc and ~/.bashrc.

       When bash is started non-interactively, to  run  a  shell  script,  for
       example, it looks for the variable BASH_ENV in the environment, expands
       its value if it appears there, and uses the expanded value as the  name
       of  a  file  to  read  and  execute.   Bash behaves as if the following
       command were executed:
              if [ -n "$BASH_ENV" ]; then . "$BASH_ENV"; fi
       but the value of the PATH variable is not used to search for  the  file
       name.

       If  bash  is  invoked  with  the name sh, it tries to mimic the startup
       behavior of historical versions of sh as  closely  as  possible,  while
       conforming  to  the  POSIX  standard  as  well.   When  invoked  as  an
       interactive login shell, or a non-interactive shell  with  the  --login
       option,   it   first   attempts  to  read  and  execute  commands  from
       /etc/profile and ~/.profile, in that order.  The --noprofile option may
       be used to inhibit this behavior.  When invoked as an interactive shell
       with the name sh, bash looks for the variable ENV, expands its value if
       it  is  defined,  and  uses the expanded value as the name of a file to
       read and execute.  Since a shell invoked as sh does not attempt to read
       and  execute commands from any other startup files, the --rcfile option
       has no effect.  A non-interactive shell invoked with the name  sh  does
       not  attempt to read any other startup files.  When invoked as sh, bash
       enters posix mode after the startup files are read.

       When bash is started in posix mode, as with the  --posix  command  line
       option, it follows the POSIX standard for startup files.  In this mode,
       interactive shells expand the ENV variable and commands  are  read  and
       executed  from  the  file  whose  name is the expanded value.  No other
       startup files are read.

       Bash attempts to determine when it is being run with its standard input
       connected  to a a network connection, as if by the remote shell daemon,
       usually rshd, or the secure shell daemon sshd.  If bash  determines  it
       is  being  run  in  this  fashion,  it reads and executes commands from
       ~/.bashrc and ~/.bashrc, if these files exist  and  are  readable.   It
       will  not  do  this if invoked as sh.  The --norc option may be used to
       inhibit this behavior, and the --rcfile option may  be  used  to  force
       another  file  to be read, but rshd does not generally invoke the shell
       with those options or allow them to be specified.

       If the shell is started with the effective user (group) id not equal to
       the real user (group) id, and the -p option is not supplied, no startup
       files are read, shell functions are not inherited from the environment,
       the  SHELLOPTS  variable, if it appears in the environment, is ignored,
       and the effective user id is set to the real user id.  If the -p option
       is  supplied  at  invocation, the startup behavior is the same, but the
       effective user id is not reset.

DEFINITIONS

       The  following  definitions  are  used  throughout  the  rest  of  this
       document.
       blank  A space or tab.
       word   A  sequence  of  characters  considered  as a single unit by the
              shell.  Also known as a token.
       name   A  word  consisting  only   of   alphanumeric   characters   and
              underscores,  and  beginning  with an alphabetic character or an
              underscore.  Also referred to as an identifier.
       metacharacter
              A character that, when unquoted, separates words.   One  of  the
              following:
              |  & ; ( ) < > space tab
       control operator
              A  token  that  performs  a  control function.  It is one of the
              following symbols:
              || & && ; ;; ( ) | |& <newline>

RESERVED WORDS

       Reserved words are words that have a special meaning to the shell.  The
       following words are recognized as reserved when unquoted and either the
       first word of a simple command (see SHELL GRAMMAR below) or  the  third
       word of a case or for command:

       !  case  do done elif else esac fi for function if in select then until
       while { } time [[ ]]

SHELL GRAMMAR

   Simple Commands
       A simple  command  is  a  sequence  of  optional  variable  assignments
       followed by blank-separated words and redirections, and terminated by a
       control operator.  The first word specifies the command to be executed,
       and  is  passed  as  argument  zero.  The remaining words are passed as
       arguments to the invoked command.

       The return value of a simple command is its exit status,  or  128+n  if
       the command is terminated by signal n.

   Pipelines
       A  pipeline  is  a sequence of one or more commands separated by one of
       the control operators | or |&.  The format for a pipeline is:

              [time [-p]] [ ! ] command [ [||&] command2 ... ]

       The standard output of command is connected via a pipe to the  standard
       input   of   command2.    This   connection  is  performed  before  any
       redirections specified by the command (see REDIRECTION below).   If  |&
       is  used,  the  standard  error  of  command is connected to command2’s
       standard input through the pipe; it is  shorthand  for  2>&1  |.   This
       implicit  redirection  of  the  standard  error  is performed after any
       redirections specified by the command.

       The return status of a pipeline is the exit status of the last command,
       unless  the  pipefail  option  is enabled.  If pipefail is enabled, the
       pipeline’s return status is the value of the last  (rightmost)  command
       to  exit  with  a  non-zero  status,  or  zero  if  all  commands  exit
       successfully.  If the reserved word !  precedes a  pipeline,  the  exit
       status  of  that pipeline is the logical negation of the exit status as
       described above.  The shell waits for all commands in the  pipeline  to
       terminate before returning a value.

       If  the  time reserved word precedes a pipeline, the elapsed as well as
       user and system time consumed by its execution are  reported  when  the
       pipeline  terminates.   The -p option changes the output format to that
       specified by POSIX.  The TIMEFORMAT variable may be  set  to  a  format
       string  that  specifies how the timing information should be displayed;
       see the description of TIMEFORMAT under Shell Variables below.

       Each command in a pipeline is executed as a separate process (i.e.,  in
       a subshell).

   Lists
       A  list  is a sequence of one or more pipelines separated by one of the
       operators ;, &, &&, or ││, and optionally terminated by one of ;, &, or
       <newline>.

       Of these list operators, && and ││ have equal precedence, followed by ;
       and &, which have equal precedence.

       A sequence of one or more newlines may appear in a list  instead  of  a
       semicolon to delimit commands.

       If  a  command  is  terminated  by  the  control  operator &, the shell
       executes the command in the background in a subshell.  The  shell  does
       not  wait  for  the  command  to  finish,  and  the return status is 0.
       Commands separated by a ; are executed sequentially;  the  shell  waits
       for  each  command to terminate in turn.  The return status is the exit
       status of the last command executed.

       AND and OR lists are sequences of one of more  pipelines  separated  by
       the  &&  and  ││ control operators, respectively.  AND and OR lists are
       executed with left associativity.  An AND list has the form

              command1 && command2

       command2 is executed if, and only if, command1 returns an  exit  status
       of zero.

       An OR list has the form

              command1 ││ command2

       command2  is  executed  if and only if command1 returns a non-zero exit
       status.  The return status of AND and OR lists is the  exit  status  of
       the last command executed in the list.

   Compound Commands
       A compound command is one of the following:

       (list) list   is  executed  in  a  subshell  environment  (see  COMMAND
              EXECUTION ENVIRONMENT below).  Variable assignments and  builtin
              commands  that  affect  the shell’s environment do not remain in
              effect after the command completes.  The return  status  is  the
              exit status of list.

       { list; }
              list  is simply executed in the current shell environment.  list
              must be terminated with a newline or semicolon.  This  is  known
              as  a  group  command.   The return status is the exit status of
              list.  Note that unlike the metacharacters ( and ), { and }  are
              reserved words and must occur where a reserved word is permitted
              to be recognized.  Since they do not cause a  word  break,  they
              must  be  separated  from  list  by  whitespace or another shell
              metacharacter.

       ((expression))
              The expression is evaluated according  to  the  rules  described
              below   under  ARITHMETIC  EVALUATION.   If  the  value  of  the
              expression is non-zero, the return status is  0;  otherwise  the
              return   status  is  1.   This  is  exactly  equivalent  to  let
              "expression".

       [[ expression ]]
              Return a status of 0 or 1 depending on  the  evaluation  of  the
              conditional  expression expression.  Expressions are composed of
              the primaries described  below  under  CONDITIONAL  EXPRESSIONS.
              Word  splitting  and pathname expansion are not performed on the
              words between the [[ and  ]];  tilde  expansion,  parameter  and
              variable  expansion, arithmetic expansion, command substitution,
              process  substitution,  and   quote   removal   are   performed.
              Conditional  operators  such  as  -f  must  be  unquoted  to  be
              recognized as primaries.

              When the == and != operators are used, the string to  the  right
              of the operator is considered a pattern and matched according to
              the rules described below under Pattern Matching.  If the  shell
              option  nocasematch  is  enabled, the match is performed without
              regard to the case of alphabetic characters.  The  return  value
              is  0  if  the  string  matches  (==) or does not match (!=) the
              pattern, and 1 otherwise.  Any part of the pattern may be quoted
              to force it to be matched as a string.

              An  additional  binary operator, =~, is available, with the same
              precedence as == and !=.  When it is used,  the  string  to  the
              right   of  the  operator  is  considered  an  extended  regular
              expression and matched accordingly (as in regex(3)).  The return
              value  is  0 if the string matches the pattern, and 1 otherwise.
              If  the  regular  expression  is  syntactically  incorrect,  the
              conditional expression’s return value is 2.  If the shell option
              nocasematch is enabled, the match is performed without regard to
              the  case of alphabetic characters.  Any part of the pattern may
              be quoted to force it to be matched  as  a  string.   Substrings
              matched  by  parenthesized  subexpressions  within  the  regular
              expression are saved in the array  variable  BASH_REMATCH.   The
              element  of  BASH_REMATCH  with  index  0  is the portion of the
              string matching the entire regular expression.  The  element  of
              BASH_REMATCH  with index n is the portion of the string matching
              the nth parenthesized subexpression.

              Expressions may  be  combined  using  the  following  operators,
              listed in decreasing order of precedence:

              ( expression )
                     Returns  the  value  of  expression.  This may be used to
                     override the normal precedence of operators.
              ! expression
                     True if expression is false.
              expression1 && expression2
                     True if both expression1 and expression2 are true.
              expression1 || expression2
                     True if either expression1 or expression2 is true.

              The && and || operators do not evaluate expression2 if the value
              of  expression1  is  sufficient to determine the return value of
              the entire conditional expression.

       for name [ in word ] ; do list ; done
              The list of words following in is expanded, generating a list of
              items.  The variable name is set to each element of this list in
              turn, and list is  executed  each  time.   If  the  in  word  is
              omitted,  the for command executes list once for each positional
              parameter that is set (see PARAMETERS below).  The return status
              is  the  exit  status of the last command that executes.  If the
              expansion of the items following in results in an empty list, no
              commands are executed, and the return status is 0.

       for (( expr1 ; expr2 ; expr3 )) ; do list ; done
              First, the arithmetic expression expr1 is evaluated according to
              the rules described  below  under  ARITHMETIC  EVALUATION.   The
              arithmetic  expression  expr2 is then evaluated repeatedly until
              it evaluates to zero.  Each time expr2 evaluates to  a  non-zero
              value,  list  is executed and the arithmetic expression expr3 is
              evaluated.  If any expression is omitted, it behaves  as  if  it
              evaluates to 1.  The return value is the exit status of the last
              command in list that  is  executed,  or  false  if  any  of  the
              expressions is invalid.

       select name [ in word ] ; do list ; done
              The list of words following in is expanded, generating a list of
              items.  The set of expanded words is  printed  on  the  standard
              error,  each  preceded  by a number.  If the in word is omitted,
              the positional parameters are printed  (see  PARAMETERS  below).
              The  PS3  prompt  is  then  displayed  and  a line read from the
              standard input.  If the line consists of a number  corresponding
              to  one of the displayed words, then the value of name is set to
              that word.  If the line is  empty,  the  words  and  prompt  are
              displayed  again.   If  EOF is read, the command completes.  Any
              other value read causes name to be set to null.  The  line  read
              is saved in the variable REPLY.  The list is executed after each
              selection until a break command is executed.  The exit status of
              select  is the exit status of the last command executed in list,
              or zero if no commands were executed.

       case word in [ [(] pattern [ | pattern ] ... ) list ;; ] ... esac
              A case command first expands word, and tries to match it against
              each  pattern  in  turn,  using  the  same matching rules as for
              pathname expansion (see Pathname Expansion below).  The word  is
              expanded   using   tilde   expansion,   parameter  and  variable
              expansion,  arithmetic   substitution,   command   substitution,
              process  substitution  and quote removal.  Each pattern examined
              is  expanded  using  tilde  expansion,  parameter  and  variable
              expansion,  arithmetic  substitution,  command substitution, and
              process  substitution.   If  the  shell  option  nocasematch  is
              enabled,  the  match  is performed without regard to the case of
              alphabetic characters.  When a match is found, the corresponding
              list  is  executed.   If  the ;; operator is used, no subsequent
              matches are attempted after the first pattern match.   Using  ;&
              in  place  of  ;;  causes  execution  to  continue with the list
              associated with the next set of patterns.  Using ;;& in place of
              ;;  causes  the  shell  to  test  the  next  pattern list in the
              statement,  if  any,  and  execute  any  associated  list  on  a
              successful  match.   The  exit  status  is  zero  if  no pattern
              matches.  Otherwise, it is the exit status of the  last  command
              executed in list.

       if list; then list; [ elif list; then list; ] ... [ else list; ] fi
              The  if  list is executed.  If its exit status is zero, the then
              list is executed.  Otherwise, each  elif  list  is  executed  in
              turn,  and  if  its  exit status is zero, the corresponding then
              list is executed and the command completes.  Otherwise, the else
              list  is  executed,  if  present.   The  exit status is the exit
              status of the last command executed, or  zero  if  no  condition
              tested true.

       while list; do list; done
       until list; do list; done
              The  while  command continuously executes the do list as long as
              the last command in list returns an exit status  of  zero.   The
              until command is identical to the while command, except that the
              test is negated; the do list is executed as  long  as  the  last
              command in list returns a non-zero exit status.  The exit status
              of the while and until commands is the exit status of  the  last
              do list command executed, or zero if none was executed.

   Coprocesses
       A coprocess is a shell command preceded by the coproc reserved word.  A
       coprocess is executed asynchronously in a subshell, as if  the  command
       had  been  terminated  with the & control operator, with a two-way pipe
       established between the executing shell and the coprocess.

       The format for a coprocess is:

              coproc [NAME] command [redirections]

       This creates a coprocess named NAME.  If  NAME  is  not  supplied,  the
       default  name  is  COPROC.   NAME  must not be supplied if command is a
       simple command (see above); otherwise, it is interpreted as  the  first
       word  of  the  simple  command.  When the coproc is executed, the shell
       creates an array variable (see Arrays below) named NAME in the  context
       of  the  executing  shell.  The standard output of command is connected
       via a pipe to a file descriptor in the executing shell, and  that  file
       descriptor  is  assigned  to NAME[0].  The standard input of command is
       connected via a pipe to a file descriptor in the executing  shell,  and
       that  file descriptor is assigned to NAME[1].  This pipe is established
       before any redirections  specified  by  the  command  (see  REDIRECTION
       below).   The  file  descriptors  can be utilized as arguments to shell
       commands and redirections using standard word expansions.  The  process
       id  of  the  shell spawned to execute the coprocess is available as the
       value of the variable NAME_PID.  The wait builtin command may  be  used
       to wait for the coprocess to terminate.

       The return status of a coprocess is the exit status of command.

   Shell Function Definitions
       A  shell function is an object that is called like a simple command and
       executes a compound command with a new set  of  positional  parameters.
       Shell functions are declared as follows:

       [ function ] name () compound-command [redirection]
              This  defines a function named name.  The reserved word function
              is optional.  If the function reserved  word  is  supplied,  the
              parentheses  are  optional.   The  body  of  the function is the
              compound command compound-command (see Compound Commands above).
              That  command is usually a list of commands between { and }, but
              may  be  any  command  listed  under  Compound  Commands  above.
              compound-command  is  executed whenever name is specified as the
              name of a simple command.   Any  redirections  (see  REDIRECTION
              below)  specified  when a function is defined are performed when
              the function  is  executed.   The  exit  status  of  a  function
              definition  is  zero  unless a syntax error occurs or a readonly
              function with the same name already exists.  When executed,  the
              exit status of a function is the exit status of the last command
              executed in the body.  (See FUNCTIONS below.)

COMMENTS

       In a non-interactive shell,  or  an  interactive  shell  in  which  the
       interactive_comments  option to the shopt builtin is enabled (see SHELL
       BUILTIN COMMANDS below), a word beginning with # causes that  word  and
       all  remaining  characters  on that line to be ignored.  An interactive
       shell without the interactive_comments option enabled  does  not  allow
       comments.    The  interactive_comments  option  is  on  by  default  in
       interactive shells.

QUOTING

       Quoting is used to remove the special meaning of certain characters  or
       words  to  the shell.  Quoting can be used to disable special treatment
       for special characters, to prevent reserved words from being recognized
       as such, and to prevent parameter expansion.

       Each  of  the metacharacters listed above under DEFINITIONS has special
       meaning to the shell and must be quoted if it is to represent itself.

       When the command history  expansion  facilities  are  being  used  (see
       HISTORY  EXPANSION  below), the history expansion character, usually !,
       must be quoted to prevent history expansion.

       There are  three  quoting  mechanisms:  the  escape  character,  single
       quotes, and double quotes.

       A  non-quoted  backslash (\) is the escape character.  It preserves the
       literal value of the next character that follows, with the exception of
       <newline>.   If  a  \<newline>  pair  appears, and the backslash is not
       itself quoted, the \<newline> is treated as a line  continuation  (that
       is, it is removed from the input stream and effectively ignored).

       Enclosing  characters  in  single quotes preserves the literal value of
       each character within the quotes.  A single quote may not occur between
       single quotes, even when preceded by a backslash.

       Enclosing  characters  in  double quotes preserves the literal value of
       all characters within the quotes, with the exception of $, `,  \,  and,
       when  history  expansion  is enabled, !.  The characters $ and ` retain
       their special meaning within double quotes.  The backslash retains  its
       special  meaning only when followed by one of the following characters:
       $, `, ", \, or <newline>.  A double quote may be quoted  within  double
       quotes by preceding it with a backslash.  If enabled, history expansion
       will be performed unless an !  appearing in double  quotes  is  escaped
       using a backslash.  The backslash preceding the !  is not removed.

       The  special  parameters  *  and  @ have special meaning when in double
       quotes (see PARAMETERS below).

       Words of the form $'string' are treated specially.  The word expands to
       string,  with backslash-escaped characters replaced as specified by the
       ANSI C standard.  Backslash escape sequences, if present,  are  decoded
       as follows:
              \a     alert (bell)
              \b     backspace
              \e     an escape character
              \f     form feed
              \n     new line
              \r     carriage return
              \t     horizontal tab
              \v     vertical tab
              \\     backslash
              \'     single quote
              \nnn   the  eight-bit  character  whose value is the octal value
                     nnn (one to three digits)
              \xHH   the eight-bit character whose value  is  the  hexadecimal
                     value HH (one or two hex digits)
              \cx    a control-x character

       The  expanded  result  is  single-quoted, as if the dollar sign had not
       been present.

       A double-quoted string preceded by a dollar sign  ($)  will  cause  the
       string  to  be  translated  according  to  the  current locale.  If the
       current locale is C or POSIX, the  dollar  sign  is  ignored.   If  the
       string is translated and replaced, the replacement is double-quoted.

PARAMETERS

       A  parameter  is  an  entity  that  stores values.  It can be a name, a
       number, or one of the special characters  listed  below  under  Special
       Parameters.   A  variable is a parameter denoted by a name.  A variable
       has a value and zero or more attributes.  Attributes are assigned using
       the  declare  builtin  command  (see  declare  below  in  SHELL BUILTIN
       COMMANDS).

       A parameter is set if it has been assigned a value.  The null string is
       a  valid  value.  Once a variable is set, it may be unset only by using
       the unset builtin command (see SHELL BUILTIN COMMANDS below).

       A variable may be assigned to by a statement of the form

              name=[value]

       If value is not given, the variable is assigned the null  string.   All
       values  undergo  tilde  expansion,  parameter  and  variable expansion,
       command substitution, arithmetic  expansion,  and  quote  removal  (see
       EXPANSION  below).  If the variable has its integer attribute set, then
       value is evaluated as an arithmetic expression  even  if  the  $((...))
       expansion is not used (see Arithmetic Expansion below).  Word splitting
       is not performed, with the exception of "$@" as explained  below  under
       Special  Parameters.   Pathname expansion is not performed.  Assignment
       statements may also appear as arguments to the alias, declare, typeset,
       export, readonly, and local builtin commands.

       In  the context where an assignment statement is assigning a value to a
       shell variable or array index, the += operator can be used to append to
       or  add  to  the  variable’s  previous  value.  When += is applied to a
       variable for which  the  integer  attribute  has  been  set,  value  is
       evaluated  as  an  arithmetic  expression  and  added to the variable’s
       current value, which is also evaluated.  When += is applied to an array
       variable  using  compound assignment (see Arrays below), the variable’s
       value is not unset (as it is when using =), and new values are appended
       to  the  array  beginning at one greater than the array’s maximum index
       (for indexed arrays) or added  as  additional  key-value  pairs  in  an
       associative  array.  When applied to a string-valued variable, value is
       expanded and appended to the variable’s value.

   Positional Parameters
       A positional parameter is a parameter denoted by one  or  more  digits,
       other than the single digit 0.  Positional parameters are assigned from
       the shell’s arguments when it is invoked, and may be  reassigned  using
       the  set builtin command.  Positional parameters may not be assigned to
       with assignment statements.  The positional parameters are  temporarily
       replaced when a shell function is executed (see FUNCTIONS below).

       When  a  positional parameter consisting of more than a single digit is
       expanded, it must be enclosed in braces (see EXPANSION below).

   Special Parameters
       The shell treats several parameters specially.   These  parameters  may
       only be referenced; assignment to them is not allowed.
       *      Expands  to  the positional parameters, starting from one.  When
              the expansion occurs within  double  quotes,  it  expands  to  a
              single  word  with  the value of each parameter separated by the
              first character of the IFS special variable.  That is,  "$*"  is
              equivalent to "$1c$2c...", where c is the first character of the
              value of the IFS variable.  If IFS is unset, the parameters  are
              separated  by spaces.  If IFS is null, the parameters are joined
              without intervening separators.
       @      Expands to the positional parameters, starting from  one.   When
              the  expansion  occurs  within  double  quotes,  each  parameter
              expands to a separate word.  That is, "$@" is equivalent to "$1"
              "$2"  ...   If the double-quoted expansion occurs within a word,
              the  expansion  of  the  first  parameter  is  joined  with  the
              beginning  part  of  the original word, and the expansion of the
              last parameter is joined with the  last  part  of  the  original
              word.   When  there  are  no  positional parameters, "$@" and $@
              expand to nothing (i.e., they are removed).
       #      Expands to the number of positional parameters in decimal.
       ?      Expands to  the  exit  status  of  the  most  recently  executed
              foreground pipeline.
       -      Expands   to   the   current  option  flags  as  specified  upon
              invocation, by the set builtin command,  or  those  set  by  the
              shell itself (such as the -i option).
       $      Expands  to  the  process ID of the shell.  In a () subshell, it
              expands to  the  process  ID  of  the  current  shell,  not  the
              subshell.
       !      Expands  to  the  process  ID  of  the  most  recently  executed
              background (asynchronous) command.
       0      Expands to the name of the shell or shell script.  This  is  set
              at  shell  initialization.   If  bash  is invoked with a file of
              commands, $0 is set to the  name  of  that  file.   If  bash  is
              started with the -c option, then $0 is set to the first argument
              after the string to be executed, if one is present.   Otherwise,
              it  is  set  to  the  file name used to invoke bash, as given by
              argument zero.
       _      At shell startup, set to the absolute pathname  used  to  invoke
              the  shell  or  shell  script  being  executed  as passed in the
              environment or argument list.  Subsequently, expands to the last
              argument  to the previous command, after expansion.  Also set to
              the full pathname used  to  invoke  each  command  executed  and
              placed  in  the  environment  exported  to  that  command.  When
              checking mail, this parameter holds the name of  the  mail  file
              currently being checked.

   Shell Variables
       The following variables are set by the shell:

       BASH   Expands  to  the  full file name used to invoke this instance of
              bash.
       BASHPID
              Expands to the process id of the  current  bash  process.   This
              differs  from  $$ under certain circumstances, such as subshells
              that do not require bash to be re-initialized.
       BASH_ALIASES
              An associative array variable whose members  correspond  to  the
              internal  list  of  aliases  as  maintained by the alias builtin
              Elements added to this array appear in the alias list; unsetting
              array  elements cause aliases to be removed from the alias list.
       BASH_ARGC
              An array variable whose values are the number of  parameters  in
              each frame of the current bash execution call stack.  The number
              of parameters to  the  current  subroutine  (shell  function  or
              script  executed  with  . or source) is at the top of the stack.
              When a subroutine is executed, the number of  parameters  passed
              is pushed onto BASH_ARGC.  The shell sets BASH_ARGC only when in
              extended debugging mode (see the  description  of  the  extdebug
              option to the shopt builtin below)
       BASH_ARGV
              An  array  variable  containing  all  of  the  parameters in the
              current bash execution call stack.  The final parameter  of  the
              last  subroutine  call  is  at  the  top of the stack; the first
              parameter of  the  initial  call  is  at  the  bottom.   When  a
              subroutine  is executed, the parameters supplied are pushed onto
              BASH_ARGV.  The shell  sets  BASH_ARGV  only  when  in  extended
              debugging  mode  (see  the description of the extdebug option to
              the shopt builtin below)
       BASH_CMDS
              An associative array variable whose members  correspond  to  the
              internal  hash  table  of  commands  as  maintained  by the hash
              builtin.  Elements added to this array appear in the hash table;
              unsetting  array  elements cause commands to be removed from the
              hash table.
       BASH_COMMAND
              The command currently being executed or about  to  be  executed,
              unless the shell is executing a command as the result of a trap,
              in which case it is the command executing at  the  time  of  the
              trap.
       BASH_EXECUTION_STRING
              The command argument to the -c invocation option.
       BASH_LINENO
              An  array  variable whose members are the line numbers in source
              files   corresponding    to    each    member    of    FUNCNAME.
              ${BASH_LINENO[$i]}  is  the line number in the source file where
              ${FUNCNAME[$i]}   was   called   (or   ${BASH_LINENO[$i-1]}   if
              referenced  within  another  shell function).  The corresponding
              source file name is ${BASH_SOURCE[$i]}.  Use  LINENO  to  obtain
              the current line number.
       BASH_REMATCH
              An  array  variable  whose members are assigned by the =~ binary
              operator to the [[ conditional command.  The element with  index
              0  is  the  portion  of  the  string matching the entire regular
              expression.  The element with index n  is  the  portion  of  the
              string  matching  the  nth  parenthesized  subexpression.   This
              variable is read-only.
       BASH_SOURCE
              An  array  variable  whose  members  are  the  source  filenames
              corresponding to the elements in the FUNCNAME array variable.
       BASH_SUBSHELL
              Incremented  by one each time a subshell or subshell environment
              is spawned.  The initial value is 0.
       BASH_VERSINFO
              A readonly array variable whose members hold version information
              for  this  instance  of  bash.  The values assigned to the array
              members are as follows:
              BASH_VERSINFO[0]        The major version number (the  release).
              BASH_VERSINFO[1]        The  minor version number (the version).
              BASH_VERSINFO[2]        The patch level.
              BASH_VERSINFO[3]        The build version.
              BASH_VERSINFO[4]        The release status (e.g., beta1).
              BASH_VERSINFO[5]        The value of MACHTYPE.

       BASH_VERSION
              Expands to a string describing the version of this  instance  of
              bash.

       COMP_CWORD
              An  index  into ${COMP_WORDS} of the word containing the current
              cursor position.  This  variable  is  available  only  in  shell
              functions invoked by the programmable completion facilities (see
              Programmable Completion below).

       COMP_KEY
              The key (or final key of a key  sequence)  used  to  invoke  the
              current completion function.

       COMP_LINE
              The  current  command  line.  This variable is available only in
              shell  functions  and   external   commands   invoked   by   the
              programmable  completion facilities (see Programmable Completion
              below).

       COMP_POINT
              The index  of  the  current  cursor  position  relative  to  the
              beginning  of  the  current  command.   If  the  current  cursor
              position is at the end of the current command, the value of this
              variable  is equal to ${#COMP_LINE}.  This variable is available
              only in shell functions and external  commands  invoked  by  the
              programmable  completion facilities (see Programmable Completion
              below).

       COMP_TYPE
              Set to an integer value corresponding to the type of  completion
              attempted  that  caused a completion function to be called: TAB,
              for  normal  completion,  ?,  for  listing   completions   after
              successive  tabs,  !,  for  listing alternatives on partial word
              completion,  @,  to  list  completions  if  the  word   is   not
              unmodified,  or  %,  for  menu  completion.   This  variable  is
              available only in shell functions and external commands  invoked
              by  the  programmable  completion  facilities  (see Programmable
              Completion below).

       COMP_WORDBREAKS
              The set of characters that the readline library treats  as  word
              separators  when performing word completion.  If COMP_WORDBREAKS
              is unset, it  loses  its  special  properties,  even  if  it  is
              subsequently reset.

       COMP_WORDS
              An   array   variable  (see  Arrays  below)  consisting  of  the
              individual words in the current command line.  The line is split
              into  words as readline would split it, using COMP_WORDBREAKS as
              described above.  This  variable  is  available  only  in  shell
              functions invoked by the programmable completion facilities (see
              Programmable Completion below).

       DIRSTACK
              An array variable (see  Arrays  below)  containing  the  current
              contents  of  the  directory  stack.   Directories appear in the
              stack in the order they  are  displayed  by  the  dirs  builtin.
              Assigning  to  members  of  this  array  variable may be used to
              modify directories already in the stack, but the pushd and  popd
              builtins must be used to add and remove directories.  Assignment
              to this variable will not  change  the  current  directory.   If
              DIRSTACK  is  unset, it loses its special properties, even if it
              is subsequently reset.

       EUID   Expands  to  the  effective  user  ID  of  the   current   user,
              initialized at shell startup.  This variable is readonly.

       FUNCNAME
              An  array  variable  containing the names of all shell functions
              currently in the execution call stack.  The element with index 0
              is  the  name  of  any  currently-executing shell function.  The
              bottom-most element is "main".  This variable exists only when a
              shell  function  is  executing.  Assignments to FUNCNAME have no
              effect and return an error status.  If  FUNCNAME  is  unset,  it
              loses  its special properties, even if it is subsequently reset.

       GROUPS An array variable containing the list of  groups  of  which  the
              current  user is a member.  Assignments to GROUPS have no effect
              and return an error status.  If GROUPS is unset,  it  loses  its
              special properties, even if it is subsequently reset.

       HISTCMD
              The history number, or index in the history list, of the current
              command.  If HISTCMD is unset, it loses its special  properties,
              even if it is subsequently reset.

       HOSTNAME
              Automatically set to the name of the current host.

       HOSTTYPE
              Automatically  set  to a string that uniquely describes the type
              of machine on which bash is executing.  The default  is  system-
              dependent.

       LINENO Each  time this parameter is referenced, the shell substitutes a
              decimal number representing the current sequential  line  number
              (starting  with  1)  within a script or function.  When not in a
              script or function, the value substituted is not  guaranteed  to
              be  meaningful.   If  LINENO  is  unset,  it  loses  its special
              properties, even if it is subsequently reset.

       MACHTYPE
              Automatically set to a string that fully  describes  the  system
              type  on  which  bash  is  executing,  in  the standard GNU cpu-
              company-system format.  The default is system-dependent.

       OLDPWD The previous working directory as set by the cd command.

       OPTARG The value of the last option argument processed by  the  getopts
              builtin command (see SHELL BUILTIN COMMANDS below).

       OPTIND The  index  of  the next argument to be processed by the getopts
              builtin command (see SHELL BUILTIN COMMANDS below).

       OSTYPE Automatically set to  a  string  that  describes  the  operating
              system  on  which  bash  is  executing.   The default is system-
              dependent.

       PIPESTATUS
              An array variable (see Arrays below) containing a list  of  exit
              status  values  from the processes in the most-recently-executed
              foreground pipeline (which may contain only a single command).

       PPID   The  process  ID  of  the  shell’s  parent.   This  variable  is
              readonly.

       PWD    The current working directory as set by the cd command.

       RANDOM Each time this parameter is referenced, a random integer between
              0 and 32767 is generated.  The sequence of random numbers may be
              initialized by assigning a value to RANDOM.  If RANDOM is unset,
              it loses its special properties,  even  if  it  is  subsequently
              reset.

       REPLY  Set  to  the line of input read by the read builtin command when
              no arguments are supplied.

       SECONDS
              Each time this parameter is referenced, the  number  of  seconds
              since  shell  invocation is returned.  If a value is assigned to
              SECONDS, the value returned upon subsequent  references  is  the
              number  of seconds since the assignment plus the value assigned.
              If SECONDS is unset, it loses its special properties, even if it
              is subsequently reset.

       SHELLOPTS
              A  colon-separated  list of enabled shell options.  Each word in
              the list is a valid argument  for  the  -o  option  to  the  set
              builtin command (see SHELL BUILTIN COMMANDS below).  The options
              appearing in SHELLOPTS are those reported as on by set  -o.   If
              this  variable  is  in the environment when bash starts up, each
              shell option in the list will  be  enabled  before  reading  any
              startup files.  This variable is read-only.

       SHLVL  Incremented by one each time an instance of bash is started.

       UID    Expands to the user ID of the current user, initialized at shell
              startup.  This variable is readonly.

       The following variables are used by the shell.   In  some  cases,  bash
       assigns a default value to a variable; these cases are noted below.

       BASH_ENV
              If  this parameter is set when bash is executing a shell script,
              its value is interpreted as a filename  containing  commands  to
              initialize the shell, as in ~/.bashrc.  The value of BASH_ENV is
              subjected to  parameter  expansion,  command  substitution,  and
              arithmetic  expansion  before  being interpreted as a file name.
              PATH is not used to search for the resultant file name.
       CDPATH The search path for the cd command.  This is  a  colon-separated
              list  of  directories  in  which the shell looks for destination
              directories specified by the cd  command.   A  sample  value  is
              ".:~:/usr".
       COLUMNS
              Used  by  the  select  builtin command to determine the terminal
              width when printing selection  lists.   Automatically  set  upon
              receipt of a SIGWINCH.
       COMPREPLY
              An array variable from which bash reads the possible completions
              generated by  a  shell  function  invoked  by  the  programmable
              completion facility (see Programmable Completion below).
       EMACS  If  bash  finds  this variable in the environment when the shell
              starts with value "t", it assumes that the shell is  running  in
              an emacs shell buffer and disables line editing.
       FCEDIT The default editor for the fc builtin command.
       FIGNORE
              A  colon-separated  list  of  suffixes to ignore when performing
              filename completion (see  READLINE  below).   A  filename  whose
              suffix  matches  one  of the entries in FIGNORE is excluded from
              the list  of  matched  filenames.   A  sample  value  is  ".o:~"
              (Quoting  is  needed  when  assigning  a value to this variable,
              which contains tildes).
       GLOBIGNORE
              A colon-separated list of patterns defining the set of filenames
              to be ignored by pathname expansion.  If a filename matched by a
              pathname expansion pattern also matches one of the  patterns  in
              GLOBIGNORE, it is removed from the list of matches.
       HISTCONTROL
              A  colon-separated  list  of values controlling how commands are
              saved on the history list.   If  the  list  of  values  includes
              ignorespace,  lines  which  begin with a space character are not
              saved in the history list.  A value of ignoredups  causes  lines
              matching the previous history entry to not be saved.  A value of
              ignoreboth is shorthand for ignorespace and ignoredups.  A value
              of erasedups causes all previous lines matching the current line
              to be removed from the history list before that line  is  saved.
              Any  value  not in the above list is ignored.  If HISTCONTROL is
              unset, or does not include a valid value, all lines read by  the
              shell parser are saved on the history list, subject to the value
              of HISTIGNORE.  The second and subsequent lines of a  multi-line
              compound  command  are  not tested, and are added to the history
              regardless of the value of HISTCONTROL.
       HISTFILE
              The name of the file in which  command  history  is  saved  (see
              HISTORY  below).   The  default  value  is  ~/.bash_history.  If
              unset, the command history is  not  saved  when  an  interactive
              shell exits.
       HISTFILESIZE
              The maximum number of lines contained in the history file.  When
              this  variable  is  assigned  a  value,  the  history  file   is
              truncated,  if  necessary,  by  removing  the oldest entries, to
              contain no more than that number of lines.  The default value is
              500.   The  history  file  is  also truncated to this size after
              writing it when an interactive shell exits.
       HISTIGNORE
              A colon-separated list of patterns used to decide which  command
              lines  should  be  saved  on  the history list.  Each pattern is
              anchored at the  beginning  of  the  line  and  must  match  the
              complete  line  (no  implicit ‘*’ is appended).  Each pattern is
              tested  against  the  line  after  the   checks   specified   by
              HISTCONTROL  are  applied.   In  addition  to  the  normal shell
              pattern matching characters, ‘&’ matches  the  previous  history
              line.   ‘&’  may  be escaped using a backslash; the backslash is
              removed before attempting a match.  The  second  and  subsequent
              lines  of  a multi-line compound command are not tested, and are
              added to the history regardless of the value of HISTIGNORE.
       HISTSIZE
              The number of commands to remember in the command  history  (see
              HISTORY below).  The default value is 500.
       HISTTIMEFORMAT
              If  this  variable  is  set and not null, its value is used as a
              format string for strftime(3) to print the time stamp associated
              with  each  history  entry displayed by the history builtin.  If
              this variable is set, time stamps are  written  to  the  history
              file  so they may be preserved across shell sessions.  This uses
              the history comment character  to  distinguish  timestamps  from
              other history lines.
       HOME   The home directory of the current user; the default argument for
              the cd builtin command.  The value of this variable is also used
              when performing tilde expansion.
       HOSTFILE
              Contains  the  name  of  a file in the same format as /etc/hosts
              that should be read when the shell needs to complete a hostname.
              The  list  of possible hostname completions may be changed while
              the shell is running;  the  next  time  hostname  completion  is
              attempted  after the value is changed, bash adds the contents of
              the new file to the existing list.  If HOSTFILE is set, but  has
              no value, bash attempts to read /etc/hosts to obtain the list of
              possible hostname completions.   When  HOSTFILE  is  unset,  the
              hostname list is cleared.
       IFS    The  Internal  Field  Separator  that is used for word splitting
              after expansion and to split lines  into  words  with  the  read
              builtin       command.       The      default      value      is
              ‘‘<space><tab><newline>’’.
       IGNOREEOF
              Controls the action of an interactive shell on receipt of an EOF
              character as the sole input.  If set, the value is the number of
              consecutive EOF characters which must  be  typed  as  the  first
              characters  on an input line before bash exits.  If the variable
              exists but does not have a numeric value, or has no  value,  the
              default  value  is  10.  If it does not exist, EOF signifies the
              end of input to the shell.
       INPUTRC
              The filename for  the  readline  startup  file,  overriding  the
              default of ~/.inputrc (see READLINE below).
       LANG   Used  to  determine  the  locale  category  for any category not
              specifically selected with a variable starting with LC_.
       LC_ALL This variable overrides the value of  LANG  and  any  other  LC_
              variable specifying a locale category.
       LC_COLLATE
              This  variable  determines the collation order used when sorting
              the results of pathname expansion, and determines  the  behavior
              of   range   expressions,  equivalence  classes,  and  collating
              sequences within pathname expansion and pattern matching.
       LC_CTYPE
              This variable determines the interpretation  of  characters  and
              the  behavior of character classes within pathname expansion and
              pattern matching.
       LC_MESSAGES
              This variable determines the locale used  to  translate  double-
              quoted strings preceded by a $.
       LC_NUMERIC
              This  variable  determines  the  locale category used for number
              formatting.
       LINES  Used by the select  builtin  command  to  determine  the  column
              length  for  printing  selection  lists.  Automatically set upon
              receipt of a SIGWINCH.
       MAIL   If this parameter is  set  to  a  file  name  and  the  MAILPATH
              variable  is  not  set,  bash informs the user of the arrival of
              mail in the specified file.
       MAILCHECK
              Specifies how often (in seconds)  bash  checks  for  mail.   The
              default  is  60 seconds.  When it is time to check for mail, the
              shell does so before displaying the  primary  prompt.   If  this
              variable  is  unset,  or  set  to  a  value that is not a number
              greater than or equal to zero, the shell disables mail checking.
       MAILPATH
              A  colon-separated  list  of  file names to be checked for mail.
              The message to be printed when mail arrives in a particular file
              may  be  specified  by separating the file name from the message
              with a ‘?’.  When used in the text of the message, $_ expands to
              the name of the current mailfile.  Example:
              MAILPATH='/var/mail/bfox?"You  have  mail":~/shell-mail?"$_  has
              mail!"'
              Bash supplies  a  default  value  for  this  variable,  but  the
              location of the user mail files that it uses is system dependent
              (e.g., /var/mail/$USER).
       OPTERR If set to the value 1, bash displays error messages generated by
              the  getopts builtin command (see SHELL BUILTIN COMMANDS below).
              OPTERR is initialized to 1 each time the shell is invoked  or  a
              shell script is executed.
       PATH   The  search  path for commands.  It is a colon-separated list of
              directories in which the shell looks for commands  (see  COMMAND
              EXECUTION  below).   A  zero-length (null) directory name in the
              value of PATH indicates the current directory.  A null directory
              name  may  appear  as  two  adjacent colons, or as an initial or
              trailing colon.  The default path is  system-dependent,  and  is
              set  by  the administrator who installs bash.  A common value is
              ‘‘/usr/gnu/bin:/usr/local/bin:/usr/ucb:/bin:/usr/bin’’.
       POSIXLY_CORRECT
              If this variable is in the environment  when  bash  starts,  the
              shell  enters posix mode before reading the startup files, as if
              the --posix invocation option had been supplied.  If it  is  set
              while  the  shell is running, bash enables posix mode, as if the
              command set -o posix had been executed.
       PROMPT_COMMAND
              If set, the value is executed as a command prior to issuing each
              primary prompt.
       PROMPT_DIRTRIM
              If  set  to a number greater than zero, the value is used as the
              number of trailing directory components to retain when expanding
              the  \w  and  \W  prompt  string  escapes (see PROMPTING below).
              Characters removed are replaced with an ellipsis.
       PS1    The value of this parameter is expanded  (see  PROMPTING  below)
              and  used  as  the  primary prompt string.  The default value is
              ‘‘\s-\v\$ ’’.
       PS2    The value of this parameter is expanded as with PS1 and used  as
              the secondary prompt string.  The default is ‘‘> ’’.
       PS3    The value of this parameter is used as the prompt for the select
              command (see SHELL GRAMMAR above).
       PS4    The value of this parameter is expanded  as  with  PS1  and  the
              value  is  printed  before  each command bash displays during an
              execution trace.  The  first  character  of  PS4  is  replicated
              multiple  times,  as  necessary,  to indicate multiple levels of
              indirection.  The default is ‘‘+ ’’.
       SHELL  The full pathname to the  shell  is  kept  in  this  environment
              variable.   If it is not set when the shell starts, bash assigns
              to it the full pathname of the current user’s login shell.
       TIMEFORMAT
              The  value  of  this  parameter  is  used  as  a  format  string
              specifying  how  the  timing  information for pipelines prefixed
              with  the  time  reserved  word  should  be  displayed.   The  %
              character  introduces  an  escape sequence that is expanded to a
              time value or other information.  The escape sequences and their
              meanings are as follows; the braces denote optional portions.
              %%        A literal %.
              %[p][l]R  The elapsed time in seconds.
              %[p][l]U  The number of CPU seconds spent in user mode.
              %[p][l]S  The number of CPU seconds spent in system mode.
              %P        The CPU percentage, computed as (%U + %S) / %R.

              The  optional  p is a digit specifying the precision, the number
              of fractional digits after a decimal point.  A value of 0 causes
              no decimal point or fraction to be output.  At most three places
              after the decimal point may be specified; values  of  p  greater
              than  3 are changed to 3.  If p is not specified, the value 3 is
              used.

              The optional l specifies a longer format, including minutes,  of
              the  form  MMmSS.FFs.   The value of p determines whether or not
              the fraction is included.

              If this variable is not set, bash acts as if it  had  the  value
              $'\nreal\t%3lR\nuser\t%3lU\nsys%3lS'.   If the value is null, no
              timing information is displayed.  A trailing  newline  is  added
              when the format string is displayed.

       TMOUT  If  set  to  a  value greater than zero, TMOUT is treated as the
              default timeout  for  the  read  builtin.   The  select  command
              terminates  if  input  does  not arrive after TMOUT seconds when
              input is coming from a terminal.  In an interactive  shell,  the
              value  is interpreted as the number of seconds to wait for input
              after issuing the primary prompt.  Bash terminates after waiting
              for that number of seconds if input does not arrive.

       TMPDIR If  set, Bash uses its value as the name of a directory in which
              Bash creates temporary files for the shell’s use.

       auto_resume
              This variable controls how the shell interacts with the user and
              job  control.   If  this  variable  is  set,  single word simple
              commands without redirections  are  treated  as  candidates  for
              resumption  of  an  existing stopped job.  There is no ambiguity
              allowed; if there is more than one job beginning with the string
              typed,  the job most recently accessed is selected.  The name of
              a stopped job, in this context, is  the  command  line  used  to
              start  it.   If set to the value exact, the string supplied must
              match the name of a stopped job exactly; if  set  to  substring,
              the  string supplied needs to match a substring of the name of a
              stopped  job.   The  substring  value   provides   functionality
              analogous to the %?  job identifier (see JOB CONTROL below).  If
              set to any other value, the supplied string must be a prefix  of
              a  stopped  job’s name; this provides functionality analogous to
              the %string job identifier.

       histchars
              The two or three characters which control history expansion  and
              tokenization (see HISTORY EXPANSION below).  The first character
              is the history expansion character, the character which  signals
              the  start  of  a  history  expansion, normally ‘!’.  The second
              character is the quick substitution character, which is used  as
              shorthand   for   re-running   the   previous  command  entered,
              substituting one string for another in the command.  The default
              is  ‘^’.   The  optional  third character is the character which
              indicates that the remainder of the line is a comment when found
              as  the  first  character  of a word, normally ‘#’.  The history
              comment character causes history substitution to be skipped  for
              the  remaining words on the line.  It does not necessarily cause
              the shell parser to treat the rest of the line as a comment.

   Arrays
       Bash provides one-dimensional indexed and associative array  variables.
       Any  variable may be used as an indexed array; the declare builtin will
       explicitly declare an array.  There is no maximum limit on the size  of
       an  array,  nor  any  requirement  that  members be indexed or assigned
       contiguously.  Indexed arrays are referenced using integers  (including
       arithmetic  expressions)   and  are  zero-based; associative arrays are
       referenced using arbitrary strings.

       An indexed array is created automatically if any variable  is  assigned
       to using the syntax name[subscript]=value.  The subscript is treated as
       an arithmetic expression that must evaluate to a number greater than or
       equal  to zero.  To explicitly declare an indexed array, use declare -a
       name (see SHELL BUILTIN COMMANDS below).  declare -a name[subscript] is
       also accepted; the subscript is ignored.

       Associative arrays are created using declare -A name.

       Attributes may be specified for an array variable using the declare and
       readonly builtins.  Each attribute applies to all members of an  array.

       Arrays   are  assigned  to  using  compound  assignments  of  the  form
       name=(value1  ...  valuen),  where  each   value   is   of   the   form
       [subscript]=string.   Indexed  array  assignments  do  not  require the
       bracket and subscript.   When  assigning  to  indexed  arrays,  if  the
       optional  brackets  and  subscript are supplied, that index is assigned
       to; otherwise the index of the  element  assigned  is  the  last  index
       assigned to by the statement plus one.  Indexing starts at zero.

       When assigning to an associative array, the subscript is required.

       This  syntax is also accepted by the declare builtin.  Individual array
       elements may be assigned  to  using  the  name[subscript]=value  syntax
       introduced above.

       Any  element  of  an  array may be referenced using ${name[subscript]}.
       The braces are required to avoid conflicts with pathname expansion.  If
       subscript  is  @  or *, the word expands to all members of name.  These
       subscripts differ only when the word appears within double quotes.   If
       the word is double-quoted, ${name[*]} expands to a single word with the
       value of each array member separated by the first character of the  IFS
       special  variable,  and  ${name[@]}  expands  each element of name to a
       separate word.  When there are no array members, ${name[@]} expands  to
       nothing.   If  the  double-quoted  expansion  occurs within a word, the
       expansion of the first parameter is joined with the beginning  part  of
       the  original  word,  and the expansion of the last parameter is joined
       with the last part of the original word.   This  is  analogous  to  the
       expansion  of  the  special  parameters * and @ (see Special Parameters
       above).     ${#name[subscript]}    expands    to    the    length    of
       ${name[subscript]}.   If  subscript  is  *  or  @, the expansion is the
       number of elements in the array.  Referencing an array variable without
       a  subscript is equivalent to referencing the array with a subscript of
       0.

       The unset builtin is used to  destroy  arrays.   unset  name[subscript]
       destroys  the  array element at index subscript.  Care must be taken to
       avoid unwanted side effects caused by filename generation.  unset name,
       where  name is an array, or unset name[subscript], where subscript is *
       or @, removes the entire array.

       The declare, local, and readonly builtins each accept a  -a  option  to
       specify  an  indexed  array  and  a -A option to specify an associative
       array.  The read builtin accepts a -a option to assign a list of  words
       read from the standard input to an array.  The set and declare builtins
       display array values in  a  way  that  allows  them  to  be  reused  as
       assignments.

EXPANSION

       Expansion is performed on the command line after it has been split into
       words.  There are seven kinds of expansion performed: brace  expansion,
       tilde    expansion,   parameter   and   variable   expansion,   command
       substitution,  arithmetic  expansion,  word  splitting,  and   pathname
       expansion.

       The   order   of  expansions  is:  brace  expansion,  tilde  expansion,
       parameter, variable and arithmetic expansion and  command  substitution
       (done  in  a  left-to-right  fashion),  word  splitting,  and  pathname
       expansion.

       On systems that can  support  it,  there  is  an  additional  expansion
       available: process substitution.

       Only brace expansion, word splitting, and pathname expansion can change
       the number of words of the expansion; other expansions expand a  single
       word  to a single word.  The only exceptions to this are the expansions
       of "$@" and "${name[@]}" as explained above (see PARAMETERS).

   Brace Expansion
       Brace expansion is a  mechanism  by  which  arbitrary  strings  may  be
       generated.   This  mechanism  is similar to pathname expansion, but the
       filenames generated need not exist.  Patterns to be brace expanded take
       the form of an optional preamble, followed by either a series of comma-
       separated strings or a sequence expression between a  pair  of  braces,
       followed  by  an optional postscript.  The preamble is prefixed to each
       string contained within the braces, and the postscript is then appended
       to each resulting string, expanding left to right.

       Brace  expansions  may  be nested.  The results of each expanded string
       are not sorted;  left  to  right  order  is  preserved.   For  example,
       a{d,c,b}e expands into ‘ade ace abe’.

       A  sequence expression takes the form {x..y[..incr]}, where x and y are
       either integers or single characters, and incr, an optional  increment,
       is  an  integer.  When integers are supplied, the expression expands to
       each number between x and  y,  inclusive.   Supplied  integers  may  be
       prefixed with 0 to force each term to have the same width.  When either
       x or y begins with a zero, the shell attempts to  force  all  generated
       terms  to  contain  the  same  number  of  digits,  zero-padding  where
       necessary.  When characters are supplied,  the  expression  expands  to
       each character lexicographically between x and y, inclusive.  Note that
       both x and y must be of the same type.  When the increment is supplied,
       it  is used as the difference between each term.  The default increment
       is 1 or -1 as appropriate.

       Brace expansion is performed  before  any  other  expansions,  and  any
       characters special to other expansions are preserved in the result.  It
       is strictly textual.  Bash does not apply any syntactic  interpretation
       to the context of the expansion or the text between the braces.

       A  correctly-formed  brace  expansion must contain unquoted opening and
       closing braces, and at least one unquoted comma  or  a  valid  sequence
       expression.   Any incorrectly formed brace expansion is left unchanged.
       A { or , may be quoted with a backslash to prevent its being considered
       part  of  a  brace  expression.   To  avoid  conflicts  with  parameter
       expansion,  the  string  ${  is  not  considered  eligible  for   brace
       expansion.

       This construct is typically used as shorthand when the common prefix of
       the strings to be generated is longer than in the above example:

              mkdir /usr/local/src/bash/{old,new,dist,bugs}
       or
              chown root /usr/{ucb/{ex,edit},lib/{ex?.?*,how_ex}}

       Brace expansion introduces a  slight  incompatibility  with  historical
       versions  of sh.  sh does not treat opening or closing braces specially
       when they appear as part of a word, and preserves them in  the  output.
       Bash  removes  braces  from  words as a consequence of brace expansion.
       For example, a word entered to sh as file{1,2} appears  identically  in
       the  output.  The same word is output as file1 file2 after expansion by
       bash.  If strict compatibility with sh is desired, start bash with  the
       +B  option  or  disable  brace  expansion with the +B option to the set
       command (see SHELL BUILTIN COMMANDS below).

   Tilde Expansion
       If a word begins with an unquoted tilde character  (‘~’),  all  of  the
       characters  preceding  the  first unquoted slash (or all characters, if
       there is no unquoted slash) are considered a tilde-prefix.  If none  of
       the  characters  in  the tilde-prefix are quoted, the characters in the
       tilde-prefix following the tilde are treated as a possible login  name.
       If  this  login name is the null string, the tilde is replaced with the
       value of the  shell  parameter  HOME.   If  HOME  is  unset,  the  home
       directory  of  the  user  executing  the  shell is substituted instead.
       Otherwise,  the  tilde-prefix  is  replaced  with  the  home  directory
       associated with the specified login name.

       If  the  tilde-prefix  is  a  ‘~+’, the value of the shell variable PWD
       replaces the tilde-prefix.  If the tilde-prefix is a ‘~-’, the value of
       the  shell  variable  OLDPWD,  if  it  is  set, is substituted.  If the
       characters following the tilde in the tilde-prefix consist of a  number
       N,  optionally prefixed by a ‘+’ or a ‘-’, the tilde-prefix is replaced
       with the corresponding element from the directory stack, as it would be
       displayed  by  the  dirs  builtin  invoked  with the tilde-prefix as an
       argument.  If the characters following the tilde  in  the  tilde-prefix
       consist of a number without a leading ‘+’ or ‘-’, ‘+’ is assumed.

       If the login name is invalid, or the tilde expansion fails, the word is
       unchanged.

       Each  variable  assignment  is  checked  for  unquoted   tilde-prefixes
       immediately  following  a  :  or  the  first  =.  In these cases, tilde
       expansion is also performed.  Consequently, one may use file names with
       tildes  in  assignments  to  PATH,  MAILPATH, and CDPATH, and the shell
       assigns the expanded value.

   Parameter Expansion
       The ‘$’ character introduces parameter expansion, command substitution,
       or  arithmetic  expansion.  The parameter name or symbol to be expanded
       may be enclosed in braces, which are optional but serve to protect  the
       variable  to be expanded from characters immediately following it which
       could be interpreted as part of the name.

       When braces are used, the matching ending brace is the  first  ‘}’  not
       escaped  by  a  backslash  or within a quoted string, and not within an
       embedded  arithmetic  expansion,  command  substitution,  or  parameter
       expansion.

       ${parameter}
              The  value of parameter is substituted.  The braces are required
              when parameter is a positional  parameter  with  more  than  one
              digit, or when parameter is followed by a character which is not
              to be interpreted as part of its name.

       If the first character of parameter is an exclamation point, a level of
       variable  indirection  is  introduced.   Bash  uses  the  value  of the
       variable formed from the rest of parameter as the name of the variable;
       this  variable  is  then expanded and that value is used in the rest of
       the substitution, rather than the value of parameter itself.   This  is
       known as indirect expansion.  The exceptions to this are the expansions
       of ${!prefix*} and ${!name[@]} described below.  The exclamation  point
       must   immediately   follow  the  left  brace  in  order  to  introduce
       indirection.

       In each of the  cases  below,  word  is  subject  to  tilde  expansion,
       parameter expansion, command substitution, and arithmetic expansion.

       When  not  performing  substring  expansion, using the forms documented
       below, bash tests for a parameter that is unset or null.  Omitting  the
       colon results in a test only for a parameter that is unset.

       ${parameter:-word}
              Use  Default  Values.   If  parameter  is  unset  or  null,  the
              expansion of word  is  substituted.   Otherwise,  the  value  of
              parameter is substituted.
       ${parameter:=word}
              Assign  Default  Values.   If  parameter  is  unset or null, the
              expansion of word  is  assigned  to  parameter.   The  value  of
              parameter   is  then  substituted.   Positional  parameters  and
              special parameters may not be assigned to in this way.
       ${parameter:?word}
              Display Error if Null or Unset.  If parameter is null or  unset,
              the  expansion  of  word (or a message to that effect if word is
              not present) is written to the standard error and the shell,  if
              it is not interactive, exits.  Otherwise, the value of parameter
              is substituted.
       ${parameter:+word}
              Use Alternate Value.  If parameter is null or unset, nothing  is
              substituted, otherwise the expansion of word is substituted.
       ${parameter:offset}
       ${parameter:offset:length}
              Substring  Expansion.   Expands  to  up  to length characters of
              parameter starting at the character  specified  by  offset.   If
              length  is  omitted,  expands  to  the  substring  of  parameter
              starting at the  character  specified  by  offset.   length  and
              offset  are  arithmetic  expressions  (see ARITHMETIC EVALUATION
              below).  length must evaluate to a number greater than or  equal
              to  zero.   If  offset evaluates to a number less than zero, the
              value is used as  an  offset  from  the  end  of  the  value  of
              parameter.   Arithmetic  expressions  starting  with a - must be
              separated by whitespace from the preceding : to be distinguished
              from  the  Use Default Values expansion.  If parameter is @, the
              result is length positional parameters beginning at offset.   If
              parameter  is  an  indexed array name subscripted by @ or *, the
              result is  the  length  members  of  the  array  beginning  with
              ${parameter[offset]}.   A  negative  offset is taken relative to
              one greater than the  maximum  index  of  the  specified  array.
              Substring  expansion  applied  to  an associative array produces
              undefined  results.   Note  that  a  negative  offset  must   be
              separated  from  the  colon by at least one space to avoid being
              confused with the :- expansion.   Substring  indexing  is  zero-
              based  unless  the positional parameters are used, in which case
              the indexing starts at 1 by default.  If offset is  0,  and  the
              positional parameters are used, $0 is prefixed to the list.

       ${!prefix*}
       ${!prefix@}
              Names  matching prefix.  Expands to the names of variables whose
              names begin with prefix, separated by the first character of the
              IFS  special variable.  When @ is used and the expansion appears
              within double quotes, each variable name expands to  a  separate
              word.

       ${!name[@]}
       ${!name[*]}
              List  of  array  keys.  If name is an array variable, expands to
              the list of array indices (keys) assigned in name.  If  name  is
              not  an  array,  expands to 0 if name is set and null otherwise.
              When @ is used and the expansion appears within  double  quotes,
              each key expands to a separate word.

       ${#parameter}
              Parameter  length.   The  length  in  characters of the value of
              parameter is substituted.  If parameter is *  or  @,  the  value
              substituted   is   the  number  of  positional  parameters.   If
              parameter is an array name subscripted by  *  or  @,  the  value
              substituted is the number of elements in the array.

       ${parameter#word}
       ${parameter##word}
              Remove matching prefix pattern.  The word is expanded to produce
              a pattern just as in pathname expansion.  If the pattern matches
              the  beginning of the value of parameter, then the result of the
              expansion is the expanded value of parameter with  the  shortest
              matching  pattern  (the  ‘‘#’’  case)  or  the  longest matching
              pattern (the ‘‘##’’ case) deleted.  If parameter is @ or *,  the
              pattern   removal   operation  is  applied  to  each  positional
              parameter in turn, and the expansion is the resultant list.   If
              parameter  is  an  array  variable  subscripted with @ or *, the
              pattern removal operation is applied to each member of the array
              in turn, and the expansion is the resultant list.

       ${parameter%word}
       ${parameter%%word}
              Remove matching suffix pattern.  The word is expanded to produce
              a pattern just as in pathname expansion.  If the pattern matches
              a  trailing portion of the expanded value of parameter, then the
              result of the expansion is the expanded value of parameter  with
              the  shortest  matching  pattern (the ‘‘%’’ case) or the longest
              matching pattern (the ‘‘%%’’ case) deleted.  If parameter  is  @
              or   *,  the  pattern  removal  operation  is  applied  to  each
              positional parameter in turn, and the expansion is the resultant
              list.   If  parameter is an array variable subscripted with @ or
              *, the pattern removal operation is applied to  each  member  of
              the array in turn, and the expansion is the resultant list.

       ${parameter/pattern/string}
              Pattern  substitution.   The  pattern  is  expanded to produce a
              pattern just as in pathname expansion.   Parameter  is  expanded
              and  the  longest match of pattern against its value is replaced
              with string.  If pattern begins with /, all matches  of  pattern
              are  replaced  with  string.   Normally  only the first match is
              replaced.  If pattern begins  with  #,  it  must  match  at  the
              beginning of the expanded value of parameter.  If pattern begins
              with %, it must match at  the  end  of  the  expanded  value  of
              parameter.   If  string  is null, matches of pattern are deleted
              and the / following pattern may be omitted.  If parameter  is  @
              or  *,  the substitution operation is applied to each positional
              parameter in turn, and the expansion is the resultant list.   If
              parameter  is  an  array  variable  subscripted with @ or *, the
              substitution operation is applied to each member of the array in
              turn, and the expansion is the resultant list.

       ${parameter^pattern}
       ${parameter^^pattern}
       ${parameter,pattern}
       ${parameter,,pattern}
              Case   modification.    This  expansion  modifies  the  case  of
              alphabetic characters in parameter.  The pattern is expanded  to
              produce a pattern just as in pathname expansion.  The ^ operator
              converts lowercase letters matching pattern to uppercase; the  ,
              operator  converts matching uppercase letters to lowercase.  The
              ^^ and ,, expansions  convert  each  matched  character  in  the
              expanded  value;  the  ^ and , expansions match and convert only
              the first character in  the  expanded  value..   If  pattern  is
              omitted,  it is treated like a ?, which matches every character.
              If parameter is @ or  *,  the  case  modification  operation  is
              applied  to each positional parameter in turn, and the expansion
              is the resultant  list.   If  parameter  is  an  array  variable
              subscripted  with  @  or  *,  the case modification operation is
              applied to each member of the array in turn, and  the  expansion
              is the resultant list.

   Command Substitution
       Command  substitution  allows  the  output  of a command to replace the
       command name.  There are two forms:

              $(command)
       or
              `command`

       Bash performs the expansion by  executing  command  and  replacing  the
       command  substitution with the standard output of the command, with any
       trailing newlines deleted.  Embedded newlines are not deleted, but they
       may  be  removed during word splitting.  The command substitution $(cat
       file) can be replaced by the equivalent but faster $(< file).

       When the old-style backquote form of substitution  is  used,  backslash
       retains  its  literal  meaning except when followed by $, `, or \.  The
       first backquote not preceded by  a  backslash  terminates  the  command
       substitution.   When  using the $(command) form, all characters between
       the parentheses make up the command; none are treated specially.

       Command substitutions may be nested.  To nest when using the backquoted
       form, escape the inner backquotes with backslashes.

       If  the  substitution  appears within double quotes, word splitting and
       pathname expansion are not performed on the results.

   Arithmetic Expansion
       Arithmetic expansion allows the evaluation of an arithmetic  expression
       and  the  substitution  of  the  result.   The  format  for  arithmetic
       expansion is:

              $((expression))

       The old format $[expression] is  deprecated  and  will  be  removed  in
       upcoming versions of bash.

       The  expression  is  treated  as if it were within double quotes, but a
       double quote inside the parentheses  is  not  treated  specially.   All
       tokens in the expression undergo parameter expansion, string expansion,
       command substitution, and quote removal.  Arithmetic expansions may  be
       nested.

       The  evaluation  is performed according to the rules listed below under
       ARITHMETIC EVALUATION.  If expression is invalid, bash prints a message
       indicating failure and no substitution occurs.

   Process Substitution
       Process  substitution  is supported on systems that support named pipes
       (FIFOs) or the /dev/fd method of naming open files.  It takes the  form
       of  <(list)  or  >(list).   The  process  list is run with its input or
       output connected to a FIFO or some file in /dev/fd.  The name  of  this
       file  is  passed as an argument to the current command as the result of
       the expansion.  If the >(list) form is used, writing to the  file  will
       provide  input  for list.  If the <(list) form is used, the file passed
       as an argument should be read to obtain the output of list.

       When available, process substitution is performed  simultaneously  with
       parameter  and variable expansion, command substitution, and arithmetic
       expansion.

   Word Splitting
       The  shell  scans  the  results   of   parameter   expansion,   command
       substitution, and arithmetic expansion that did not occur within double
       quotes for word splitting.

       The shell treats each character of IFS as a delimiter, and  splits  the
       results of the other expansions into words on these characters.  If IFS
       is unset, or its value is exactly <space><tab><newline>,  the  default,
       then  sequences  of  <space>, <tab>, and <newline> at the beginning and
       end of the results of the previous  expansions  are  ignored,  and  any
       sequence  of  IFS  characters  not  at  the  beginning or end serves to
       delimit words.  If IFS  has  a  value  other  than  the  default,  then
       sequences of the whitespace characters space and tab are ignored at the
       beginning and end of the word, as long as the whitespace  character  is
       in  the  value  of IFS (an IFS whitespace character).  Any character in
       IFS that is not IFS whitespace, along with any adjacent IFS  whitespace
       characters,  delimits a field.  A sequence of IFS whitespace characters
       is also treated as a delimiter.  If the value of IFS is null,  no  word
       splitting occurs.

       Explicit  null  arguments  (""  or '') are retained.  Unquoted implicit
       null arguments, resulting from the expansion of parameters that have no
       values,  are  removed.  If a parameter with no value is expanded within
       double quotes, a null argument results and is retained.

       Note that if no expansion occurs, no splitting is performed.

   Pathname Expansion
       After word splitting, unless the -f option has  been  set,  bash  scans
       each  word  for the characters *, ?, and [.  If one of these characters
       appears, then the word is regarded as a pattern, and replaced  with  an
       alphabetically  sorted  list of file names matching the pattern.  If no
       matching file names are found, and the shell  option  nullglob  is  not
       enabled,  the  word  is left unchanged.  If the nullglob option is set,
       and no matches are found, the word is removed.  If the  failglob  shell
       option  is  set,  and no matches are found, an error message is printed
       and the command is not executed.  If the  shell  option  nocaseglob  is
       enabled,  the  match  is  performed  without  regard  to  the  case  of
       alphabetic characters.  Note that when using range expressions like [a-
       z] (see below), letters of the other case may be included, depending on
       the setting of  LC_COLLATE.   When  a  pattern  is  used  for  pathname
       expansion,  the  character ‘‘.’’  at the start of a name or immediately
       following a slash must be matched explicitly, unless the  shell  option
       dotglob  is  set.   When  matching a pathname, the slash character must
       always be matched explicitly.  In other cases, the ‘‘.’’  character  is
       not  treated specially.  See the description of shopt below under SHELL
       BUILTIN  COMMANDS  for  a  description  of  the  nocaseglob,  nullglob,
       failglob, and dotglob shell options.

       The  GLOBIGNORE  shell variable may be used to restrict the set of file
       names matching a pattern.  If GLOBIGNORE is  set,  each  matching  file
       name  that  also  matches  one of the patterns in GLOBIGNORE is removed
       from the list of matches.  The file names ‘‘.’’  and ‘‘..’’  are always
       ignored  when  GLOBIGNORE  is  set  and  not  null.   However,  setting
       GLOBIGNORE to a non-null value has the effect of enabling  the  dotglob
       shell  option,  so  all  other  file names beginning with a ‘‘.’’  will
       match.  To get the old behavior of ignoring file names beginning with a
       ‘‘.’’,  make  ‘‘.*’’   one  of the patterns in GLOBIGNORE.  The dotglob
       option is disabled when GLOBIGNORE is unset.

       Pattern Matching

       Any character that appears in a pattern, other than the special pattern
       characters  described below, matches itself.  The NUL character may not
       occur in a pattern.  A backslash escapes the following  character;  the
       escaping  backslash  is  discarded  when matching.  The special pattern
       characters must be quoted if they are to be matched literally.

       The special pattern characters have the following meanings:

       *      Matches  any  string,  including  the  null  string.   When  the
              globstar  shell  option  is enabled, and * is used in a filename
              expansion context, two adjacent *s used as a single pattern will
              match all files and zero or more directories and subdirectories.
              If followed by a /, two adjacent *s will match only  directories
              and subdirectories.
       ?      Matches any single character.
       [...]  Matches   any  one  of  the  enclosed  characters.   A  pair  of
              characters separated by a hyphen denotes a range expression; any
              character  that  sorts  between those two characters, inclusive,
              using the current locale’s collating sequence and character set,
              is matched.  If the first character following the [ is a !  or a
              ^ then any character not enclosed is matched.  The sorting order
              of  characters in range expressions is determined by the current
              locale and the value of the LC_COLLATE shell variable,  if  set.
              A  -  may  be  matched  by  including  it  as  the first or last
              character in the set.  A ] may be matched by including it as the
              first character in the set.

              Within  [  and  ],  character classes can be specified using the
              syntax [:class:], where class is one of  the  following  classes
              defined in the POSIX standard:
              alnum  alpha  ascii  blank  cntrl  digit graph lower print punct
              space upper word xdigit
              A character class matches any character belonging to that class.
              The  word  character  class  matches  letters,  digits,  and the
              character _.

              Within [ and ], an equivalence class can be specified using  the
              syntax  [=c=],  which  matches  all  characters  with  the  same
              collation weight (as defined  by  the  current  locale)  as  the
              character c.

              Within  [  and  ],  the  syntax [.symbol.] matches the collating
              symbol symbol.

       If the extglob shell option is enabled using the shopt builtin, several
       extended  pattern  matching operators are recognized.  In the following
       description, a pattern-list is a list of one or more patterns separated
       by  a  |.   Composite  patterns  may be formed using one or more of the
       following sub-patterns:

              ?(pattern-list)
                     Matches zero or one occurrence of the given patterns
              *(pattern-list)
                     Matches zero or more occurrences of the given patterns
              +(pattern-list)
                     Matches one or more occurrences of the given patterns
              @(pattern-list)
                     Matches one of the given patterns
              !(pattern-list)
                     Matches anything except one of the given patterns

   Quote Removal
       After  the  preceding  expansions,  all  unquoted  occurrences  of  the
       characters  \,  ',  and  "  that  did  not result from one of the above
       expansions are removed.

REDIRECTION

       Before a command is executed, its input and output  may  be  redirected
       using  a  special  notation  interpreted by the shell.  Redirection may
       also be used to open and close files for the  current  shell  execution
       environment.  The following redirection operators may precede or appear
       anywhere within a simple command or may follow a command.  Redirections
       are processed in the order they appear, from left to right.

       In  the  following  descriptions,  if  the  file  descriptor  number is
       omitted, and the first character of the redirection operator is <,  the
       redirection  refers  to the standard input (file descriptor 0).  If the
       first character of the  redirection  operator  is  >,  the  redirection
       refers to the standard output (file descriptor 1).

       The   word   following   the  redirection  operator  in  the  following
       descriptions, unless otherwise noted, is subjected to brace  expansion,
       tilde  expansion, parameter expansion, command substitution, arithmetic
       expansion, quote removal, pathname expansion, and word  splitting.   If
       it expands to more than one word, bash reports an error.

       Note  that  the order of redirections is significant.  For example, the
       command

              ls > dirlist 2>&1

       directs both standard output and standard error to  the  file  dirlist,
       while the command

              ls 2>&1 > dirlist

       directs  only the standard output to file dirlist, because the standard
       error was duplicated from  the  standard  output  before  the  standard
       output was redirected to dirlist.

       Bash  handles  several  filenames  specially  when  they  are  used  in
       redirections, as described in the following table:

              /dev/fd/fd
                     If  fd  is  a  valid  integer,  file  descriptor  fd   is
                     duplicated.
              /dev/stdin
                     File descriptor 0 is duplicated.
              /dev/stdout
                     File descriptor 1 is duplicated.
              /dev/stderr
                     File descriptor 2 is duplicated.
              /dev/tcp/host/port
                     If host is a valid hostname or Internet address, and port
                     is an integer port number or service name, bash  attempts
                     to open a TCP connection to the corresponding socket.
              /dev/udp/host/port
                     If host is a valid hostname or Internet address, and port
                     is an integer port number or service name, bash  attempts
                     to open a UDP connection to the corresponding socket.

       A failure to open or create a file causes the redirection to fail.

       Redirections  using file descriptors greater than 9 should be used with
       care, as they  may  conflict  with  file  descriptors  the  shell  uses
       internally.

       Note that the exec builtin command can make redirections take effect in
       the current shell.

   Redirecting Input
       Redirection of input causes  the  file  whose  name  results  from  the
       expansion of word to be opened for reading on file descriptor n, or the
       standard input (file descriptor 0) if n is not specified.

       The general format for redirecting input is:

              [n]<word

   Redirecting Output
       Redirection of output causes the  file  whose  name  results  from  the
       expansion of word to be opened for writing on file descriptor n, or the
       standard output (file descriptor 1) if n is not specified.  If the file
       does  not exist it is created; if it does exist it is truncated to zero
       size.

       The general format for redirecting output is:

              [n]>word

       If the redirection operator is >, and the noclobber option to  the  set
       builtin  has  been enabled, the redirection will fail if the file whose
       name results from the expansion of word exists and is a  regular  file.
       If the redirection operator is >|, or the redirection operator is > and
       the noclobber option to the set builtin command  is  not  enabled,  the
       redirection is attempted even if the file named by word exists.

   Appending Redirected Output
       Redirection  of  output  in  this  fashion  causes  the file whose name
       results from the expansion of word to be opened for appending  on  file
       descriptor  n,  or  the standard output (file descriptor 1) if n is not
       specified.  If the file does not exist it is created.

       The general format for appending output is:

              [n]>>word

   Redirecting Standard Output and Standard Error
       This construct allows both the standard output (file descriptor 1)  and
       the  standard  error output (file descriptor 2) to be redirected to the
       file whose name is the expansion of word.

       There are two formats for  redirecting  standard  output  and  standard
       error:

              &>word
       and
              >&word

       Of  the  two  forms,  the  first  is  preferred.   This is semantically
       equivalent to

              >word 2>&1

   Appending Standard Output and Standard Error
       This construct allows both the standard output (file descriptor 1)  and
       the  standard  error  output  (file descriptor 2) to be appended to the
       file whose name is the expansion of word.

       The format for appending standard output and standard error is:

              &>>word

       This is semantically equivalent to

              >>word 2>&1

   Here Documents
       This type of redirection instructs the shell to  read  input  from  the
       current source until a line containing only delimiter (with no trailing
       blanks) is seen.  All of the lines read up to that point are then  used
       as the standard input for a command.

       The format of here-documents is:

              <<[-]word
                      here-document
              delimiter

       No  parameter expansion, command substitution, arithmetic expansion, or
       pathname expansion is performed on word.  If any characters in word are
       quoted,  the  delimiter is the result of quote removal on word, and the
       lines in the here-document are not expanded.  If word is unquoted,  all
       lines  of  the  here-document  are  subjected  to  parameter expansion,
       command substitution, and arithmetic expansion.  In  the  latter  case,
       the  character  sequence  \<newline>  is ignored, and \ must be used to
       quote the characters \, $, and `.

       If the redirection operator is <<-, then all leading tab characters are
       stripped  from  input  lines  and  the line containing delimiter.  This
       allows here-documents within shell scripts to be indented in a  natural
       fashion.

   Here Strings
       A variant of here documents, the format is:

              <<<word

       The word is expanded and supplied to the command on its standard input.

   Duplicating File Descriptors
       The redirection operator

              [n]<&word

       is used to duplicate input file descriptors.  If word expands to one or
       more  digits,  the file descriptor denoted by n is made to be a copy of
       that file descriptor.  If the digits in word  do  not  specify  a  file
       descriptor  open  for  input,  a  redirection  error  occurs.   If word
       evaluates to -, file descriptor n is closed.  If n  is  not  specified,
       the standard input (file descriptor 0) is used.

       The operator

              [n]>&word

       is  used  similarly  to duplicate output file descriptors.  If n is not
       specified, the standard output (file descriptor 1)  is  used.   If  the
       digits  in  word  do  not  specify a file descriptor open for output, a
       redirection error occurs.  As a special case, if n is omitted, and word
       does not expand to one or more digits, the standard output and standard
       error are redirected as described previously.

   Moving File Descriptors
       The redirection operator

              [n]<&digit-

       moves the file descriptor digit to file descriptor n, or  the  standard
       input (file descriptor 0) if n is not specified.  digit is closed after
       being duplicated to n.

       Similarly, the redirection operator

              [n]>&digit-

       moves the file descriptor digit to file descriptor n, or  the  standard
       output (file descriptor 1) if n is not specified.

   Opening File Descriptors for Reading and Writing
       The redirection operator

              [n]<>word

       causes  the  file  whose name is the expansion of word to be opened for
       both reading and writing on file descriptor n, or on file descriptor  0
       if n is not specified.  If the file does not exist, it is created.

ALIASES

       Aliases  allow a string to be substituted for a word when it is used as
       the first word of a simple command.  The  shell  maintains  a  list  of
       aliases  that  may  be set and unset with the alias and unalias builtin
       commands (see SHELL BUILTIN COMMANDS below).  The first  word  of  each
       simple  command, if unquoted, is checked to see if it has an alias.  If
       so, that word is replaced by the text of the alias.  The characters  /,
       $,  `,  and = and any of the shell metacharacters or quoting characters
       listed above may not appear in an alias name.  The replacement text may
       contain  any  valid  shell  input, including shell metacharacters.  The
       first word of the replacement text is tested for aliases,  but  a  word
       that  is  identical to an alias being expanded is not expanded a second
       time.  This means that one may alias ls to ls  -F,  for  instance,  and
       bash  does  not try to recursively expand the replacement text.  If the
       last character of the alias value is a blank,  then  the  next  command
       word following the alias is also checked for alias expansion.

       Aliases are created and listed with the alias command, and removed with
       the unalias command.

       There is no mechanism for using arguments in the replacement text.   If
       arguments  are  needed,  a shell function should be used (see FUNCTIONS
       below).

       Aliases are not expanded when the shell is not interactive, unless  the
       expand_aliases  shell option is set using shopt (see the description of
       shopt under SHELL BUILTIN COMMANDS below).

       The rules concerning the definition and use  of  aliases  are  somewhat
       confusing.   Bash  always  reads  at  least  one complete line of input
       before executing any  of  the  commands  on  that  line.   Aliases  are
       expanded  when  a command is read, not when it is executed.  Therefore,
       an alias definition appearing on the same line as another command  does
       not  take  effect  until  the next line of input is read.  The commands
       following the alias definition on that line are not affected by the new
       alias.   This  behavior  is  also an issue when functions are executed.
       Aliases are expanded when a function definition is read, not  when  the
       function  is  executed,  because  a  function  definition  is  itself a
       compound command.  As a consequence, aliases defined in a function  are
       not  available  until  after  that  function  is executed.  To be safe,
       always put alias definitions on a separate line, and do not  use  alias
       in compound commands.

       For almost every purpose, aliases are superseded by shell functions.

FUNCTIONS

       A  shell  function,  defined  as  described  above under SHELL GRAMMAR,
       stores a series of commands for later execution.  When the  name  of  a
       shell  function  is used as a simple command name, the list of commands
       associated with that function name is executed.  Functions are executed
       in  the  context  of  the  current  shell; no new process is created to
       interpret them (contrast this with the execution of  a  shell  script).
       When  a  function is executed, the arguments to the function become the
       positional parameters during its execution.  The special parameter # is
       updated  to reflect the change.  Special parameter 0 is unchanged.  The
       first element of the FUNCNAME variable  is  set  to  the  name  of  the
       function  while  the  function  is executing.  All other aspects of the
       shell execution environment are identical between a  function  and  its
       caller  with  the  exception  that  the DEBUG and RETURN traps (see the
       description of the trap builtin under SHELL BUILTIN COMMANDS below) are
       not  inherited  unless  the function has been given the trace attribute
       (see the description of the declare builtin below) or the -o  functrace
       shell  option  has been enabled with the set builtin (in which case all
       functions inherit the DEBUG and RETURN traps).

       Variables local to the function may be declared with the local  builtin
       command.  Ordinarily, variables and their values are shared between the
       function and its caller.

       If the builtin command return is executed in a function,  the  function
       completes  and  execution  resumes  with  the  next  command  after the
       function call.  Any command associated with the RETURN trap is executed
       before execution resumes.  When a function completes, the values of the
       positional parameters and the special parameter # are restored  to  the
       values they had prior to the function’s execution.

       Function  names and definitions may be listed with the -f option to the
       declare or typeset builtin commands.   The  -F  option  to  declare  or
       typeset  will  list  the function names only (and optionally the source
       file and line  number,  if  the  extdebug  shell  option  is  enabled).
       Functions  may  be  exported  so that subshells automatically have them
       defined  with  the  -f  option  to  the  export  builtin.   A  function
       definition  may  be  deleted  using the -f option to the unset builtin.
       Note that shell functions and variables with the same name  may  result
       in  multiple identically-named entries in the environment passed to the
       shell’s children.  Care should be taken in cases where this may cause a
       problem.

       Functions  may  be  recursive.   No  limit  is imposed on the number of
       recursive calls.

ARITHMETIC EVALUATION

       The shell allows arithmetic expressions to be evaluated, under  certain
       circumstances  (see the let and declare builtin commands and Arithmetic
       Expansion).  Evaluation is done in fixed-width integers with  no  check
       for  overflow, though division by 0 is trapped and flagged as an error.
       The operators and their precedence, associativity, and values  are  the
       same  as in the C language.  The following list of operators is grouped
       into levels of equal-precedence operators.  The levels  are  listed  in
       order of decreasing precedence.

       id++ id--
              variable post-increment and post-decrement
       ++id --id
              variable pre-increment and pre-decrement
       - +    unary minus and plus
       ! ~    logical and bitwise negation
       **     exponentiation
       * / %  multiplication, division, remainder
       + -    addition, subtraction
       << >>  left and right bitwise shifts
       <= >= < >
              comparison
       == !=  equality and inequality
       &      bitwise AND
       ^      bitwise exclusive OR
       |      bitwise OR
       &&     logical AND
       ||     logical OR
       expr?expr:expr
              conditional operator
       = *= /= %= += -= <<= >>= &= ^= |=
              assignment
       expr1 , expr2
              comma

       Shell  variables  are  allowed  as  operands;  parameter  expansion  is
       performed before the expression is evaluated.   Within  an  expression,
       shell  variables  may  also  be  referenced  by  name without using the
       parameter expansion syntax.  A shell variable that  is  null  or  unset
       evaluates  to  0  when  referenced  by name without using the parameter
       expansion  syntax.   The  value  of  a  variable  is  evaluated  as  an
       arithmetic  expression  when it is referenced, or when a variable which
       has been given the integer attribute using declare  -i  is  assigned  a
       value.   A  null  value evaluates to 0.  A shell variable need not have
       its integer attribute turned on to be used in an expression.

       Constants with a leading 0 are interpreted as octal numbers.  A leading
       0x  or  0X  denotes  hexadecimal.   Otherwise,  numbers  take  the form
       [base#]n, where base is a decimal number between 2 and 64  representing
       the  arithmetic  base,  and  n  is  a number in that base.  If base# is
       omitted, then  base  10  is  used.   The  digits  greater  than  9  are
       represented  by the lowercase letters, the uppercase letters, @, and _,
       in that order.  If base is less than or  equal  to  36,  lowercase  and
       uppercase  letters  may  be  used  interchangeably to represent numbers
       between 10 and 35.

       Operators are evaluated in order  of  precedence.   Sub-expressions  in
       parentheses  are  evaluated first and may override the precedence rules
       above.

CONDITIONAL EXPRESSIONS

       Conditional expressions are used by the [[  compound  command  and  the
       test  and [ builtin commands to test file attributes and perform string
       and arithmetic comparisons.  Expressions are formed from the  following
       unary  or  binary  primaries.   If  any  file  argument  to  one of the
       primaries is of the form /dev/fd/n, then file descriptor n is  checked.
       If  the  file  argument  to  one of the primaries is one of /dev/stdin,
       /dev/stdout, or /dev/stderr, file descriptor 0, 1, or 2,  respectively,
       is checked.

       Unless  otherwise  specified,  primaries  that  operate on files follow
       symbolic links and operate on the target of the link, rather  than  the
       link itself.

       See  the description of the test builtin command (section SHELL BUILTIN
       COMMANDS  below)  for  the  handling  of  parameters   (i.e.    missing
       parameters).

       -a file
              True if file exists.
       -b file
              True if file exists and is a block special file.
       -c file
              True if file exists and is a character special file.
       -d file
              True if file exists and is a directory.
       -e file
              True if file exists.
       -f file
              True if file exists and is a regular file.
       -g file
              True if file exists and is set-group-id.
       -h file
              True if file exists and is a symbolic link.
       -k file
              True if file exists and its ‘‘sticky’’ bit is set.
       -p file
              True if file exists and is a named pipe (FIFO).
       -r file
              True if file exists and is readable.
       -s file
              True if file exists and has a size greater than zero.
       -t fd  True if file descriptor fd is open and refers to a terminal.
       -u file
              True if file exists and its set-user-id bit is set.
       -w file
              True if file exists and is writable.
       -x file
              True if file exists and is executable.
       -O file
              True if file exists and is owned by the effective user id.
       -G file
              True if file exists and is owned by the effective group id.
       -L file
              True if file exists and is a symbolic link.
       -S file
              True if file exists and is a socket.
       -N file
              True  if  file  exists  and  has been modified since it was last
              read.
       file1 -nt file2
              True if file1 is newer (according  to  modification  date)  than
              file2, or if file1 exists and file2 does not.
       file1 -ot file2
              True  if file1 is older than file2, or if file2 exists and file1
              does not.
       file1 -ef file2
              True if file1 and file2 refer  to  the  same  device  and  inode
              numbers.
       -o optname
              True  if  shell  option  optname  is  enabled.   See the list of
              options under the description  of  the  -o  option  to  the  set
              builtin below.
       -z string
              True if the length of string is zero.
       string
       -n string
              True if the length of string is non-zero.

       string1 == string2
              True if the strings are equal.  = may be used in place of == for
              strict POSIX compliance.

       string1 != string2
              True if the strings are not equal.

       string1 < string2
              True if string1 sorts before string2  lexicographically  in  the
              current locale.

       string1 > string2
              True  if  string1  sorts  after string2 lexicographically in the
              current locale.

       arg1 OP arg2
              OP is one of -eq, -ne, -lt, -le, -gt, or -ge.  These  arithmetic
              binary  operators return true if arg1 is equal to, not equal to,
              less than, less than or equal to, greater than, or greater  than
              or  equal  to arg2, respectively.  Arg1 and arg2 may be positive
              or negative integers.

SIMPLE COMMAND EXPANSION

       When a simple command is executed, the  shell  performs  the  following
       expansions, assignments, and redirections, from left to right.

       1.     The  words  that  the  parser has marked as variable assignments
              (those preceding the command name) and  redirections  are  saved
              for later processing.

       2.     The  words that are not variable assignments or redirections are
              expanded.  If any words remain after expansion, the  first  word
              is  taken  to be the name of the command and the remaining words
              are the arguments.

       3.     Redirections are performed as described above under REDIRECTION.

       4.     The text after the = in each variable assignment undergoes tilde
              expansion, parameter expansion, command substitution, arithmetic
              expansion,  and  quote  removal  before  being  assigned  to the
              variable.

       If no command name results, the variable assignments affect the current
       shell   environment.    Otherwise,  the  variables  are  added  to  the
       environment of the executed command and do not affect the current shell
       environment.  If any of the assignments attempts to assign a value to a
       readonly variable, an error occurs, and the command exits with  a  non-
       zero status.

       If  no  command  name  results,  redirections are performed, but do not
       affect the current shell environment.  A redirection error  causes  the
       command to exit with a non-zero status.

       If  there is a command name left after expansion, execution proceeds as
       described  below.   Otherwise,  the  command  exits.   If  one  of  the
       expansions  contained  a  command  substitution, the exit status of the
       command is the exit status of the last command substitution  performed.
       If there were no command substitutions, the command exits with a status
       of zero.

COMMAND EXECUTION

       After a command has been split into words, if it results  in  a  simple
       command  and  an  optional list of arguments, the following actions are
       taken.

       If the command name contains no slashes, the shell attempts  to  locate
       it.   If  there  exists a shell function by that name, that function is
       invoked as described above in FUNCTIONS.  If the name does not match  a
       function,  the shell searches for it in the list of shell builtins.  If
       a match is found, that builtin is invoked.

       If the name is neither a shell function nor a builtin, and contains  no
       slashes,  bash  searches  each  element  of  the  PATH  for a directory
       containing an executable file by that name.  Bash uses a hash table  to
       remember  the  full pathnames of executable files (see hash under SHELL
       BUILTIN COMMANDS below).  A full search of the directories in  PATH  is
       performed  only  if the command is not found in the hash table.  If the
       search is unsuccessful, the shell searches for a defined shell function
       named command_not_found_handle.  If that function exists, it is invoked
       with the original command and the original command’s arguments  as  its
       arguments,  and  the  function’s exit status becomes the exit status of
       the shell.  If that function is not defined, the shell prints an  error
       message and returns an exit status of 127.

       If  the  search  is  successful, or if the command name contains one or
       more slashes, the shell  executes  the  named  program  in  a  separate
       execution  environment.   Argument  0 is set to the name given, and the
       remaining arguments to the command are set to the arguments  given,  if
       any.

       If  this  execution fails because the file is not in executable format,
       and the file is not a directory, it is assumed to be a shell script,  a
       file  containing  shell commands.  A subshell is spawned to execute it.
       This subshell reinitializes itself, so that the effect is as if  a  new
       shell  had  been  invoked to handle the script, with the exception that
       the locations of commands remembered by  the  parent  (see  hash  below
       under SHELL BUILTIN COMMANDS) are retained by the child.

       If  the program is a file beginning with #!, the remainder of the first
       line specifies an interpreter for the program.  The shell executes  the
       specified  interpreter  on  operating  systems  that do not handle this
       executable format themselves.  The arguments to the interpreter consist
       of  a  single  optional  argument following the interpreter name on the
       first line of the  program,  followed  by  the  name  of  the  program,
       followed by the command arguments, if any.

COMMAND EXECUTION ENVIRONMENT

       The   shell  has  an  execution  environment,  which  consists  of  the
       following:

       ·      open files inherited by the shell at invocation, as modified  by
              redirections supplied to the exec builtin

       ·      the  current  working directory as set by cd, pushd, or popd, or
              inherited by the shell at invocation

       ·      the file creation mode mask as set by umask  or  inherited  from
              the shell’s parent

       ·      current traps set by trap

       ·      shell parameters that are set by variable assignment or with set
              or inherited from the shell’s parent in the environment

       ·      shell functions defined during execution or inherited  from  the
              shell’s parent in the environment

       ·      options  enabled  at  invocation  (either  by  default  or  with
              command-line arguments) or by set

       ·      options enabled by shopt

       ·      shell aliases defined with alias

       ·      various process IDs, including those  of  background  jobs,  the
              value of $$, and the value of $PPID

       When  a  simple command other than a builtin or shell function is to be
       executed, it is  invoked  in  a  separate  execution  environment  that
       consists  of  the  following.   Unless  otherwise noted, the values are
       inherited from the shell.

       ·      the shell’s open files, plus  any  modifications  and  additions
              specified by redirections to the command

       ·      the current working directory

       ·      the file creation mode mask

       ·      shell  variables  and  functions  marked  for export, along with
              variables exported for the command, passed in the environment

       ·      traps caught by the shell are reset to the values inherited from
              the shell’s parent, and traps ignored by the shell are ignored

       A  command  invoked  in  this  separate  environment  cannot affect the
       shell’s execution environment.

       Command  substitution,   commands   grouped   with   parentheses,   and
       asynchronous  commands  are invoked in a subshell environment that is a
       duplicate of the shell environment, except that  traps  caught  by  the
       shell  are reset to the values that the shell inherited from its parent
       at invocation.  Builtin commands that are invoked as part of a pipeline
       are  also  executed  in  a  subshell  environment.  Changes made to the
       subshell environment cannot affect the shell’s execution environment.

       Subshells spawned to execute command substitutions inherit the value of
       the  -e  option  from  the  parent shell.  When not in posix mode, Bash
       clears the -e option in such subshells.

       If a command is followed by a & and job  control  is  not  active,  the
       default  standard  input  for  the command is the empty file /dev/null.
       Otherwise, the invoked command inherits the  file  descriptors  of  the
       calling shell as modified by redirections.

ENVIRONMENT

       When  a  program  is invoked it is given an array of strings called the
       environment.   This  is  a  list  of  name-value  pairs,  of  the  form
       name=value.

       The  shell  provides  several  ways  to manipulate the environment.  On
       invocation, the shell scans its own environment and creates a parameter
       for  each  name  found,  automatically  marking  it for export to child
       processes.  Executed commands inherit the environment.  The export  and
       declare  -x  commands allow parameters and functions to be added to and
       deleted from the environment.  If the  value  of  a  parameter  in  the
       environment is modified, the new value becomes part of the environment,
       replacing the old.  The environment inherited by any  executed  command
       consists  of  the  shell’s  initial  environment,  whose  values may be
       modified in the shell, less any pairs removed  by  the  unset  command,
       plus any additions via the export and declare -x commands.

       The  environment  for  any  simple command or function may be augmented
       temporarily by prefixing it with parameter  assignments,  as  described
       above  in  PARAMETERS.   These  assignment  statements  affect only the
       environment seen by that command.

       If the -k option is set (see the set builtin command below),  then  all
       parameter  assignments are placed in the environment for a command, not
       just those that precede the command name.

       When bash invokes an external command, the variable _  is  set  to  the
       full  file  name  of  the  command  and  passed  to that command in its
       environment.

EXIT STATUS

       The exit status of an executed command is the  value  returned  by  the
       waitpid system call or equivalent function.  Exit statuses fall between
       0 and 255, though, as explained below, the shell may use  values  above
       125 specially.  Exit statuses from shell builtins and compound commands
       are also limited to this range. Under certain circumstances, the  shell
       will use special values to indicate specific failure modes.

       For the shell’s purposes, a command which exits with a zero exit status
       has succeeded.  An exit status of zero indicates success.   A  non-zero
       exit  status  indicates  failure.  When a command terminates on a fatal
       signal N, bash uses the value of 128+N as the exit status.

       If a command is not found, the child  process  created  to  execute  it
       returns  a status of 127.  If a command is found but is not executable,
       the return status is 126.

       If a command fails because of an error during expansion or redirection,
       the exit status is greater than zero.

       Shell  builtin  commands return a status of 0 (true) if successful, and
       non-zero (false) if an error occurs while they execute.   All  builtins
       return an exit status of 2 to indicate incorrect usage.

       Bash  itself  returns  the  exit  status  of the last command executed,
       unless a syntax error occurs, in which case it exits  with  a  non-zero
       value.  See also the exit builtin command below.

SIGNALS

       When  bash  is  interactive,  in  the  absence of any traps, it ignores
       SIGTERM (so that kill 0 does not kill an interactive shell), and SIGINT
       is  caught and handled (so that the wait builtin is interruptible).  In
       all cases, bash ignores SIGQUIT.  If job control  is  in  effect,  bash
       ignores SIGTTIN, SIGTTOU, and SIGTSTP.

       Non-builtin commands run by bash have signal handlers set to the values
       inherited by the shell from its parent.  When job  control  is  not  in
       effect,  asynchronous commands ignore SIGINT and SIGQUIT in addition to
       these  inherited  handlers.   Commands  run  as  a  result  of  command
       substitution ignore the keyboard-generated job control signals SIGTTIN,
       SIGTTOU, and SIGTSTP.

       The shell exits by default upon receipt of a SIGHUP.   Before  exiting,
       an  interactive  shell  resends  the  SIGHUP  to  all  jobs, running or
       stopped.  Stopped jobs are sent SIGCONT to ensure that they receive the
       SIGHUP.   To  prevent the shell from sending the signal to a particular
       job, it should be removed from the jobs table with the  disown  builtin
       (see  SHELL  BUILTIN  COMMANDS  below)  or marked to not receive SIGHUP
       using disown -h.

       If the huponexit shell option has been set with  shopt,  bash  sends  a
       SIGHUP to all jobs when an interactive login shell exits.

       If  bash is waiting for a command to complete and receives a signal for
       which a trap has been set, the trap will  not  be  executed  until  the
       command  completes.   When  bash is waiting for an asynchronous command
       via the wait builtin, the reception of a signal for which  a  trap  has
       been set will cause the wait builtin to return immediately with an exit
       status greater than 128, immediately after which the trap is  executed.

JOB CONTROL

       Job  control  refers  to  the ability to selectively stop (suspend) the
       execution of processes and continue (resume) their execution at a later
       point.   A  user  typically  employs  this  facility via an interactive
       interface supplied jointly by the system’s terminal driver and bash.

       The shell associates a job with each pipeline.  It  keeps  a  table  of
       currently  executing  jobs,  which may be listed with the jobs command.
       When bash starts a job asynchronously (in the background), it prints  a
       line that looks like:

              [1] 25647

       indicating that this job is job number 1 and that the process ID of the
       last process in the pipeline associated with this job is 25647.  All of
       the  processes  in a single pipeline are members of the same job.  Bash
       uses the job abstraction as the basis for job control.

       To facilitate the implementation of the user interface to job  control,
       the operating system maintains the notion of a current terminal process
       group ID.  Members of this process group (processes whose process group
       ID is equal to the current terminal process group ID) receive keyboard-
       generated signals such as SIGINT.  These processes are said  to  be  in
       the  foreground.  Background processes are those whose process group ID
       differs from the terminal’s; such processes  are  immune  to  keyboard-
       generated  signals.  Only foreground processes are allowed to read from
       or write to the terminal.  Background processes which attempt  to  read
       from (write to) the terminal are sent a SIGTTIN (SIGTTOU) signal by the
       terminal driver, which, unless caught, suspends the process.

       If the operating system on which bash is running supports job  control,
       bash  contains  facilities  to  use  it.   Typing the suspend character
       (typically ^Z, Control-Z)  while  a  process  is  running  causes  that
       process  to be stopped and returns control to bash.  Typing the delayed
       suspend character (typically ^Y, Control-Y) causes the  process  to  be
       stopped  when  it attempts to read input from the terminal, and control
       to be returned to bash.  The user may then manipulate the state of this
       job,  using  the  bg  command  to continue it in the background, the fg
       command to continue it in the foreground, or the kill command  to  kill
       it.   A ^Z takes effect immediately, and has the additional side effect
       of causing pending output and typeahead to be discarded.

       There are a number of ways to  refer  to  a  job  in  the  shell.   The
       character % introduces a job specification (jobspec).  Job number n may
       be referred to as %n.  A job may also be referred to using a prefix  of
       the  name  used  to  start it, or using a substring that appears in its
       command line.  For example, %ce refers to  a  stopped  ce  job.   If  a
       prefix  matches  more than one job, bash reports an error.  Using %?ce,
       on the other hand, refers to any job containing the string  ce  in  its
       command line.  If the substring matches more than one job, bash reports
       an error.  The symbols %% and %+ refer to the  shell’s  notion  of  the
       current  job,  which  is  the  last  job  stopped  while  it was in the
       foreground or started in the  background.   The  previous  job  may  be
       referenced using %-.  If there is only a single job, %+ and %- can both
       be used to refer to that job.  In output pertaining to jobs (e.g.,  the
       output  of  the jobs command), the current job is always flagged with a
       +, and the previous job with a -.  A single % (with no accompanying job
       specification) also refers to the current job.

       Simply  naming a job can be used to bring it into the foreground: %1 is
       a synonym for ‘‘fg %1’’, bringing job 1 from the  background  into  the
       foreground.   Similarly,  ‘‘%1  &’’  resumes  job  1 in the background,
       equivalent to ‘‘bg %1’’.

       The shell learns immediately whenever a job changes  state.   Normally,
       bash waits until it is about to print a prompt before reporting changes
       in a job’s status so as to not interrupt any other output.  If  the  -b
       option to the set builtin command is enabled, bash reports such changes
       immediately.  Any trap on SIGCHLD  is  executed  for  each  child  that
       exits.

       If  an  attempt to exit bash is made while jobs are stopped (or, if the
       checkjobs shell option  has  been  enabled  using  the  shopt  builtin,
       running),  the  shell  prints  a warning message, and, if the checkjobs
       option is enabled, lists the jobs and their statuses.  The jobs command
       may  then be used to inspect their status.  If a second attempt to exit
       is made without an  intervening  command,  the  shell  does  not  print
       another warning, and any stopped jobs are terminated.

PROMPTING

       When executing interactively, bash displays the primary prompt PS1 when
       it is ready to read a command, and the secondary  prompt  PS2  when  it
       needs  more  input  to  complete  a  command.  Bash allows these prompt
       strings to be customized by inserting  a  number  of  backslash-escaped
       special characters that are decoded as follows:
              \a     an ASCII bell character (07)
              \d     the  date  in "Weekday Month Date" format (e.g., "Tue May
                     26")
              \D{format}
                     the format is passed to strftime(3)  and  the  result  is
                     inserted  into the prompt string; an empty format results
                     in a locale-specific time representation.  The braces are
                     required
              \e     an ASCII escape character (033)
              \h     the hostname up to the first ‘.’
              \H     the hostname
              \j     the number of jobs currently managed by the shell
              \l     the basename of the shell’s terminal device name
              \n     newline
              \r     carriage return
              \s     the  name  of  the shell, the basename of $0 (the portion
                     following the final slash)
              \t     the current time in 24-hour HH:MM:SS format
              \T     the current time in 12-hour HH:MM:SS format
              \@     the current time in 12-hour am/pm format
              \A     the current time in 24-hour HH:MM format
              \u     the username of the current user
              \v     the version of bash (e.g., 2.00)
              \V     the release of bash, version + patch level (e.g., 2.00.0)
              \w     the  current  working  directory,  with $HOME abbreviated
                     with a tilde (uses the $PROMPT_DIRTRIM variable)
              \W     the basename of the current working directory, with $HOME
                     abbreviated with a tilde
              \!     the history number of this command
              \#     the command number of this command
              \$     if the effective UID is 0, a #, otherwise a $
              \nnn   the character corresponding to the octal number nnn
              \\     a backslash
              \[     begin  a sequence of non-printing characters, which could
                     be used to embed a terminal  control  sequence  into  the
                     prompt
              \]     end a sequence of non-printing characters

       The  command  number  and the history number are usually different: the
       history number of a command is its position in the history list,  which
       may  include  commands  restored  from  the  history  file (see HISTORY
       below), while the command number is the position  in  the  sequence  of
       commands  executed  during the current shell session.  After the string
       is  decoded,  it  is  expanded   via   parameter   expansion,   command
       substitution,  arithmetic  expansion, and quote removal, subject to the
       value of the promptvars shell option (see the description of the  shopt
       command under SHELL BUILTIN COMMANDS below).

READLINE

       This   is  the  library  that  handles  reading  input  when  using  an
       interactive shell, unless the --noediting  option  is  given  at  shell
       invocation.   Line editing is also used when using the -e option to the
       read builtin.  By default, the line editing  commands  are  similar  to
       those  of  emacs.  A vi-style line editing interface is also available.
       Line editing can be enabled at any time using the -o  emacs  or  -o  vi
       options to the set builtin (see SHELL BUILTIN COMMANDS below).  To turn
       off line editing after the shell is running, use the +o emacs or +o  vi
       options to the set builtin.

   Readline Notation
       In this section, the emacs-style notation is used to denote keystrokes.
       Control  keys  are  denoted  by  C-key,  e.g.,  C-n  means   Control-N.
       Similarly,  meta  keys  are denoted by M-key, so M-x means Meta-X.  (On
       keyboards without a meta key, M-x means ESC x, i.e., press  the  Escape
       key  then  the x key.  This makes ESC the meta prefix.  The combination
       M-C-x means ESC-Control-x, or  press  the  Escape  key  then  hold  the
       Control key while pressing the x key.)

       Readline commands may be given numeric arguments, which normally act as
       a repeat count.  Sometimes, however, it is the  sign  of  the  argument
       that  is  significant.   Passing  a negative argument to a command that
       acts in the forward direction (e.g., kill-line) causes that command  to
       act  in  a  backward direction.  Commands whose behavior with arguments
       deviates from this are noted below.

       When a command is described as killing text, the text deleted is  saved
       for possible future retrieval (yanking).  The killed text is saved in a
       kill ring.  Consecutive kills cause the text to be accumulated into one
       unit, which can be yanked all at once.  Commands which do not kill text
       separate the chunks of text on the kill ring.

   Readline Initialization
       Readline is customized by putting commands in  an  initialization  file
       (the  inputrc  file).  The name of this file is taken from the value of
       the INPUTRC variable.  If  that  variable  is  unset,  the  default  is
       ~/.inputrc.   When a program which uses the readline library starts up,
       the initialization file is read, and the key bindings and variables are
       set.   There  are  only  a few basic constructs allowed in the readline
       initialization file.  Blank lines are ignored.  Lines beginning with  a
       #  are  comments.   Lines  beginning  with  a  $  indicate  conditional
       constructs.  Other lines denote key bindings and variable settings.

       The default key-bindings may be changed with an  inputrc  file.   Other
       programs that use this library may add their own commands and bindings.

       For example, placing

              M-Control-u: universal-argument
       or
              C-Meta-u: universal-argument
       into  the  inputrc  would  make  M-C-u  execute  the  readline  command
       universal-argument.

       The  following  symbolic  character  names are recognized: RUBOUT, DEL,
       ESC, LFD, NEWLINE, RET, RETURN, SPC, SPACE, and TAB.

       In addition to command names, readline allows keys to  be  bound  to  a
       string that is inserted when the key is pressed (a macro).

   Readline Key Bindings
       The  syntax for controlling key bindings in the inputrc file is simple.
       All that is required is the name of the command or the text of a  macro
       and  a  key  sequence  to  which  it  should  be bound. The name may be
       specified in one of two ways: as a symbolic  key  name,  possibly  with
       Meta- or Control- prefixes, or as a key sequence.

       When using the form keyname:function-name or macro, keyname is the name
       of a key spelled out in English.  For example:

              Control-u: universal-argument
              Meta-Rubout: backward-kill-word
              Control-o: "> output"

       In the above example, C-u is bound to the function  universal-argument,
       M-DEL  is bound to the function backward-kill-word, and C-o is bound to
       run the macro expressed on the right hand side (that is, to insert  the
       text ‘‘> output’’ into the line).

       In  the  second  form,  "keyseq":function-name or macro, keyseq differs
       from keyname above in that strings denoting an entire key sequence  may
       be  specified  by  placing the sequence within double quotes.  Some GNU
       Emacs style key escapes can be used, as in the following  example,  but
       the symbolic character names are not recognized.

              "\C-u": universal-argument
              "\C-x\C-r": re-read-init-file
              "\e[11~": "Function Key 1"

       In this example, C-u is again bound to the function universal-argument.
       C-x C-r is bound to the function re-read-init-file, and ESC [ 1 1 ~  is
       bound to insert the text ‘‘Function Key 1’’.

       The full set of GNU Emacs style escape sequences is
              \C-    control prefix
              \M-    meta prefix
              \e     an escape character
              \\     backslash
              \"     literal "
              \'     literal '

       In  addition  to  the GNU Emacs style escape sequences, a second set of
       backslash escapes is available:
              \a     alert (bell)
              \b     backspace
              \d     delete
              \f     form feed
              \n     newline
              \r     carriage return
              \t     horizontal tab
              \v     vertical tab
              \nnn   the eight-bit character whose value is  the  octal  value
                     nnn (one to three digits)
              \xHH   the  eight-bit  character  whose value is the hexadecimal
                     value HH (one or two hex digits)

       When entering the text of a macro, single or double quotes must be used
       to  indicate  a  macro  definition.   Unquoted  text is assumed to be a
       function name.  In the macro  body,  the  backslash  escapes  described
       above  are  expanded.   Backslash will quote any other character in the
       macro text, including " and '.

       Bash allows the current  readline  key  bindings  to  be  displayed  or
       modified  with  the  bind  builtin  command.   The  editing mode may be
       switched during interactive use by using  the  -o  option  to  the  set
       builtin command (see SHELL BUILTIN COMMANDS below).

   Readline Variables
       Readline  has  variables  that  can  be  used  to further customize its
       behavior.  A variable may be set in the inputrc file with  a  statement
       of the form

              set variable-name value

       Except  where  noted,  readline variables can take the values On or Off
       (without regard to case).  Unrecognized  variable  names  are  ignored.
       When  a  variable  value  is  read,  empty  or null values, "on" (case-
       insensitive), and "1" are equivalent  to  On.   All  other  values  are
       equivalent to Off.  The variables and their default values are:

       bell-style (audible)
              Controls  what  happens when readline wants to ring the terminal
              bell.  If set to none, readline never rings the bell.  If set to
              visible,  readline  uses a visible bell if one is available.  If
              set to audible, readline attempts to ring the terminal’s bell.
       bind-tty-special-chars (On)
              If set to On, readline attempts to bind the  control  characters
              treated  specially  by  the  kernel’s  terminal  driver to their
              readline equivalents.
       comment-begin (‘‘#’’)
              The string that is inserted  when  the  readline  insert-comment
              command is executed.  This command is bound to M-# in emacs mode
              and to # in vi command mode.
       completion-ignore-case (Off)
              If set to On, readline performs filename matching and completion
              in a case-insensitive fashion.
       completion-prefix-display-length (0)
              The  length  in  characters  of  the  common prefix of a list of
              possible completions that  is  displayed  without  modification.
              When  set  to  a value greater than zero, common prefixes longer
              than this value are replaced with an  ellipsis  when  displaying
              possible completions.
       completion-query-items (100)
              This  determines  when  the  user  is  queried about viewing the
              number   of    possible    completions    generated    by    the
              possible-completions  command.   It  may  be  set to any integer
              value greater than or equal to zero.  If the number of  possible
              completions  is  greater  than  or  equal  to  the value of this
              variable, the user is asked whether or not  he  wishes  to  view
              them; otherwise they are simply listed on the terminal.
       convert-meta (On)
              If  set  to On, readline will convert characters with the eighth
              bit set to an ASCII key sequence by stripping the eighth bit and
              prefixing  an  escape  character (in effect, using escape as the
              meta prefix).
       disable-completion (Off)
              If set to On, readline will inhibit word completion.  Completion
              characters  will  be  inserted into the line as if they had been
              mapped to self-insert.
       editing-mode (emacs)
              Controls whether readline begins with  a  set  of  key  bindings
              similar to emacs or vi.  editing-mode can be set to either emacs
              or vi.
       enable-keypad (Off)
              When set to On, readline will  try  to  enable  the  application
              keypad  when it is called.  Some systems need this to enable the
              arrow keys.
       expand-tilde (Off)
              If set  to  on,  tilde  expansion  is  performed  when  readline
              attempts word completion.
       history-preserve-point (Off)
              If  set  to  on, the history code attempts to place point at the
              same location on each  history  line  retrieved  with  previous-
              history or next-history.
       history-size (0)
              Set  the  maximum number of history entries saved in the history
              list.  If set to zero, the number of entries in the history list
              is not limited.
       horizontal-scroll-mode (Off)
              When  set  to  On, makes readline use a single line for display,
              scrolling the input horizontally on a single screen line when it
              becomes  longer  than the screen width rather than wrapping to a
              new line.
       input-meta (Off)
              If set to On, readline will enable eight-bit input (that is,  it
              will  not  strip  the  high  bit  from the characters it reads),
              regardless of what the terminal claims it can support.  The name
              meta-flag is a synonym for this variable.
       isearch-terminators (‘‘C-[C-J’’)
              The  string  of  characters that should terminate an incremental
              search  without  subsequently  executing  the  character  as   a
              command.   If  this  variable  has  not  been given a value, the
              characters ESC and C-J will terminate an incremental search.
       keymap (emacs)
              Set the current readline keymap.  The set of valid keymap  names
              is    emacs,   emacs-standard,   emacs-meta,   emacs-ctlx,   vi,
              vi-command, and vi-insert.   vi  is  equivalent  to  vi-command;
              emacs  is  equivalent  to  emacs-standard.  The default value is
              emacs; the  value  of  editing-mode  also  affects  the  default
              keymap.
       mark-directories (On)
              If set to On, completed directory names have a slash appended.
       mark-modified-lines (Off)
              If  set  to  On,  history  lines  that  have  been  modified are
              displayed with a preceding asterisk (*).
       mark-symlinked-directories (Off)
              If set to On,  completed  names  which  are  symbolic  links  to
              directories  have  a  slash  appended  (subject  to the value of
              mark-directories).
       match-hidden-files (On)
              This variable, when set to On, causes readline  to  match  files
              whose  names  begin  with  a  ‘.’ (hidden files) when performing
              filename completion, unless the leading ‘.’ is supplied  by  the
              user in the filename to be completed.
       output-meta (Off)
              If  set  to On, readline will display characters with the eighth
              bit set directly rather than as a meta-prefixed escape sequence.
       page-completions (On)
              If  set  to  On,  readline  uses  an internal more-like pager to
              display a screenful of possible completions at a time.
       print-completions-horizontally (Off)
              If set to On, readline will  display  completions  with  matches
              sorted  horizontally in alphabetical order, rather than down the
              screen.
       revert-all-at-newline (Off)
              If set to on, readline will undo all changes  to  history  lines
              before  returning  when  accept-line  is  executed.  By default,
              history lines may be modified and retain individual  undo  lists
              across calls to readline.
       show-all-if-ambiguous (Off)
              This  alters  the  default behavior of the completion functions.
              If set to on, words which have more than one possible completion
              cause  the  matches  to be listed immediately instead of ringing
              the bell.
       show-all-if-unmodified (Off)
              This alters the default behavior of the completion functions  in
              a fashion similar to show-all-if-ambiguous.  If set to on, words
              which  have  more  than  one  possible  completion  without  any
              possible  partial  completion  (the  possible  completions don’t
              share  a  common  prefix)  cause  the  matches  to   be   listed
              immediately instead of ringing the bell.
       visible-stats (Off)
              If  set to On, a character denoting a file’s type as reported by
              stat(2) is  appended  to  the  filename  when  listing  possible
              completions.

   Readline Conditional Constructs
       Readline  implements  a  facility  similar in spirit to the conditional
       compilation features of the C preprocessor which  allows  key  bindings
       and  variable  settings  to be performed as the result of tests.  There
       are four parser directives used.

       $if    The $if construct allows  bindings  to  be  made  based  on  the
              editing  mode, the terminal being used, or the application using
              readline.  The text of the test extends to the end of the  line;
              no characters are required to isolate it.

              mode   The  mode=  form  of  the  $if  directive is used to test
                     whether readline is in emacs or vi  mode.   This  may  be
                     used  in  conjunction  with  the  set keymap command, for
                     instance, to  set  bindings  in  the  emacs-standard  and
                     emacs-ctlx  keymaps  only  if readline is starting out in
                     emacs mode.

              term   The term= form may be used to  include  terminal-specific
                     key bindings, perhaps to bind the key sequences output by
                     the terminal’s function keys.  The word on the right side
                     of  the  =  is  tested  against the both full name of the
                     terminal and the portion of the terminal name before  the
                     first  -.  This allows sun to match both sun and sun-cmd,
                     for instance.

              application
                     The application construct is used to include application-
                     specific  settings.   Each  program  using  the  readline
                     library sets the application name, and an  initialization
                     file can test for a particular value.  This could be used
                     to bind key sequences to functions useful for a  specific
                     program.   For instance, the following command adds a key
                     sequence that quotes the  current  or  previous  word  in
                     Bash:

                     $if Bash
                     # Quote the current or previous word
                     "\C-xq": "\eb\"\ef\""
                     $endif

       $endif This command, as seen in the previous example, terminates an $if
              command.

       $else  Commands in this branch of the $if directive are executed if the
              test fails.

       $include
              This  directive takes a single filename as an argument and reads
              commands  and  bindings  from  that  file.   For  example,   the
              following directive would read /etc/inputrc:

              $include  /etc/inputrc

   Searching
       Readline  provides  commands  for searching through the command history
       (see HISTORY below) for lines containing a specified string.  There are
       two search modes: incremental and non-incremental.

       Incremental  searches  begin  before  the  user has finished typing the
       search string.  As each  character  of  the  search  string  is  typed,
       readline  displays  the next entry from the history matching the string
       typed so far.  An incremental search requires only as  many  characters
       as needed to find the desired history entry.  The characters present in
       the value of the isearch-terminators variable are used to terminate  an
       incremental search.  If that variable has not been assigned a value the
       Escape and Control-J characters will terminate an  incremental  search.
       Control-G  will  abort  an  incremental search and restore the original
       line.  When the search is terminated, the history entry containing  the
       search string becomes the current line.

       To  find  other matching entries in the history list, type Control-S or
       Control-R as appropriate.  This will search backward or forward in  the
       history  for  the  next  entry matching the search string typed so far.
       Any other key sequence bound to a readline command will  terminate  the
       search  and  execute  that  command.   For  instance,  a  newline  will
       terminate the search and accept the line, thereby executing the command
       from the history list.

       Readline remembers the last incremental search string.  If two Control-
       Rs are typed without any intervening characters defining a  new  search
       string, any remembered search string is used.

       Non-incremental  searches read the entire search string before starting
       to search for matching history lines.  The search string may  be  typed
       by the user or be part of the contents of the current line.

   Readline Command Names
       The  following  is  a list of the names of the commands and the default
       key sequences to which  they  are  bound.   Command  names  without  an
       accompanying  key  sequence  are  unbound by default.  In the following
       descriptions, point refers to the current  cursor  position,  and  mark
       refers  to  a  cursor position saved by the set-mark command.  The text
       between the point and mark is referred to as the region.

   Commands for Moving
       beginning-of-line (C-a)
              Move to the start of the current line.
       end-of-line (C-e)
              Move to the end of the line.
       forward-char (C-f)
              Move forward a character.
       backward-char (C-b)
              Move back a character.
       forward-word (M-f)
              Move forward to the end of the next word.  Words are composed of
              alphanumeric characters (letters and digits).
       backward-word (M-b)
              Move  back  to the start of the current or previous word.  Words
              are composed of alphanumeric characters (letters and digits).
       shell-forward-word
              Move forward to the end of the next word.  Words  are  delimited
              by non-quoted shell metacharacters.
       shell-backward-word
              Move  back  to the start of the current or previous word.  Words
              are delimited by non-quoted shell metacharacters.
       clear-screen (C-l)
              Clear the screen leaving the current line  at  the  top  of  the
              screen.   With  an  argument,  refresh  the current line without
              clearing the screen.
       redraw-current-line
              Refresh the current line.

   Commands for Manipulating the History
       accept-line (Newline, Return)
              Accept the line regardless of where the cursor is.  If this line
              is  non-empty, add it to the history list according to the state
              of the HISTCONTROL variable.  If the line is a modified  history
              line, then restore the history line to its original state.
       previous-history (C-p)
              Fetch the previous command from the history list, moving back in
              the list.
       next-history (C-n)
              Fetch the next command from the history list, moving forward  in
              the list.
       beginning-of-history (M-<)
              Move to the first line in the history.
       end-of-history (M->)
              Move  to  the end of the input history, i.e., the line currently
              being entered.
       reverse-search-history (C-r)
              Search backward starting at the current  line  and  moving  ‘up’
              through  the  history  as  necessary.   This  is  an incremental
              search.
       forward-search-history (C-s)
              Search forward starting at the current line  and  moving  ‘down’
              through  the  history  as  necessary.   This  is  an incremental
              search.
       non-incremental-reverse-search-history (M-p)
              Search backward through the history starting at the current line
              using  a  non-incremental  search  for  a string supplied by the
              user.
       non-incremental-forward-search-history (M-n)
              Search forward  through  the  history  using  a  non-incremental
              search for a string supplied by the user.
       history-search-forward
              Search  forward through the history for the string of characters
              between the start of the current line and the point.  This is  a
              non-incremental search.
       history-search-backward
              Search backward through the history for the string of characters
              between the start of the current line and the point.  This is  a
              non-incremental search.
       yank-nth-arg (M-C-y)
              Insert  the  first argument to the previous command (usually the
              second word on the previous line) at point.  With an argument n,
              insert  the nth word from the previous command (the words in the
              previous command  begin  with  word  0).   A  negative  argument
              inserts the nth word from the end of the previous command.  Once
              the argument n is computed, the argument is extracted as if  the
              "!n" history expansion had been specified.
       yank-last-arg (M-., M-_)
              Insert  the last argument to the previous command (the last word
              of the  previous  history  entry).   With  an  argument,  behave
              exactly  like  yank-nth-arg.   Successive calls to yank-last-arg
              move back through the history list, inserting the last  argument
              of each line in turn.  The history expansion facilities are used
              to extract the last argument, as if the "!$"  history  expansion
              had been specified.
       shell-expand-line (M-C-e)
              Expand  the  line  as  the  shell does.  This performs alias and
              history expansion as well as all of the shell  word  expansions.
              See  HISTORY  EXPANSION  below  for  a  description  of  history
              expansion.
       history-expand-line (M-^)
              Perform history expansion on  the  current  line.   See  HISTORY
              EXPANSION below for a description of history expansion.
       magic-space
              Perform  history  expansion  on  the  current  line and insert a
              space.  See HISTORY EXPANSION below for a description of history
              expansion.
       alias-expand-line
              Perform  alias expansion on the current line.  See ALIASES above
              for a description of alias expansion.
       history-and-alias-expand-line
              Perform history and alias expansion on the current line.
       insert-last-argument (M-., M-_)
              A synonym for yank-last-arg.
       operate-and-get-next (C-o)
              Accept the current line for execution and fetch  the  next  line
              relative  to the current line from the history for editing.  Any
              argument is ignored.
       edit-and-execute-command (C-xC-e)
              Invoke an editor on the current command line,  and  execute  the
              result  as  shell  commands.   Bash  attempts to invoke $VISUAL,
              $EDITOR, and emacs as the editor, in that order.

   Commands for Changing Text
       delete-char (C-d)
              Delete the character at point.  If point is at the beginning  of
              the  line,  there  are  no  characters in the line, and the last
              character typed was not bound to delete-char, then return EOF.
       backward-delete-char (Rubout)
              Delete the character behind the cursor.  When  given  a  numeric
              argument, save the deleted text on the kill ring.
       forward-backward-delete-char
              Delete  the  character under the cursor, unless the cursor is at
              the end of the line, in which  case  the  character  behind  the
              cursor is deleted.
       quoted-insert (C-q, C-v)
              Add  the next character typed to the line verbatim.  This is how
              to insert characters like C-q, for example.
       tab-insert (C-v TAB)
              Insert a tab character.
       self-insert (a, b, A, 1, !, ...)
              Insert the character typed.
       transpose-chars (C-t)
              Drag the character before point forward over  the  character  at
              point,  moving point forward as well.  If point is at the end of
              the line, then this transposes the two characters before  point.
              Negative arguments have no effect.
       transpose-words (M-t)
              Drag  the  word  before  point past the word after point, moving
              point over that word as well.  If point is at  the  end  of  the
              line, this transposes the last two words on the line.
       upcase-word (M-u)
              Uppercase  the  current  (or  following)  word.  With a negative
              argument, uppercase the previous word, but do not move point.
       downcase-word (M-l)
              Lowercase the current (or  following)  word.   With  a  negative
              argument, lowercase the previous word, but do not move point.
       capitalize-word (M-c)
              Capitalize  the  current  (or  following) word.  With a negative
              argument, capitalize the previous word, but do not move point.
       overwrite-mode
              Toggle  overwrite  mode.   With  an  explicit  positive  numeric
              argument,  switches  to  overwrite  mode.  With an explicit non-
              positive  numeric  argument,  switches  to  insert  mode.   This
              command   affects  only  emacs  mode;  vi  mode  does  overwrite
              differently.  Each call to readline() starts in insert mode.  In
              overwrite mode, characters bound to self-insert replace the text
              at point rather than pushing the text to the right.   Characters
              bound to backward-delete-char replace the character before point
              with a space.  By default, this command is unbound.

   Killing and Yanking
       kill-line (C-k)
              Kill the text from point to the end of the line.
       backward-kill-line (C-x Rubout)
              Kill backward to the beginning of the line.
       unix-line-discard (C-u)
              Kill backward from point to the  beginning  of  the  line.   The
              killed text is saved on the kill-ring.
       kill-whole-line
              Kill  all  characters on the current line, no matter where point
              is.
       kill-word (M-d)
              Kill from point to the end of the current word,  or  if  between
              words,  to  the  end  of the next word.  Word boundaries are the
              same as those used by forward-word.
       backward-kill-word (M-Rubout)
              Kill the word behind point.  Word boundaries  are  the  same  as
              those used by backward-word.
       shell-kill-word (M-d)
              Kill  from  point  to the end of the current word, or if between
              words, to the end of the next word.   Word  boundaries  are  the
              same as those used by shell-forward-word.
       shell-backward-kill-word (M-Rubout)
              Kill  the  word  behind  point.  Word boundaries are the same as
              those used by shell-backward-word.
       unix-word-rubout (C-w)
              Kill the  word  behind  point,  using  white  space  as  a  word
              boundary.  The killed text is saved on the kill-ring.
       unix-filename-rubout
              Kill  the  word  behind  point,  using white space and the slash
              character as the word boundaries.  The killed text is  saved  on
              the kill-ring.
       delete-horizontal-space (M-\)
              Delete all spaces and tabs around point.
       kill-region
              Kill the text in the current region.
       copy-region-as-kill
              Copy the text in the region to the kill buffer.
       copy-backward-word
              Copy  the  word  before  point  to  the  kill  buffer.  The word
              boundaries are the same as backward-word.
       copy-forward-word
              Copy the word following point to  the  kill  buffer.   The  word
              boundaries are the same as forward-word.
       yank (C-y)
              Yank the top of the kill ring into the buffer at point.
       yank-pop (M-y)
              Rotate  the  kill  ring,  and  yank  the  new  top.   Only works
              following yank or yank-pop.

   Numeric Arguments
       digit-argument (M-0, M-1, ..., M--)
              Add this digit to the argument already accumulating, or start  a
              new argument.  M-- starts a negative argument.
       universal-argument
              This  is another way to specify an argument.  If this command is
              followed by one or more digits, optionally with a leading  minus
              sign,  those  digits  define  the  argument.   If the command is
              followed by digits, executing universal-argument again ends  the
              numeric  argument, but is otherwise ignored.  As a special case,
              if this command is immediately followed by a character  that  is
              neither  a  digit or minus sign, the argument count for the next
              command is multiplied by four.  The argument count is  initially
              one,  so  executing  this  function  the  first  time  makes the
              argument count four, a second  time  makes  the  argument  count
              sixteen, and so on.

   Completing
       complete (TAB)
              Attempt  to  perform  completion on the text before point.  Bash
              attempts completion treating the text as a variable (if the text
              begins  with  $), username (if the text begins with ~), hostname
              (if the text begins with @), or command (including  aliases  and
              functions) in turn.  If none of these produces a match, filename
              completion is attempted.
       possible-completions (M-?)
              List the possible completions of the text before point.
       insert-completions (M-*)
              Insert all completions of the text before point that would  have
              been generated by possible-completions.
       menu-complete
              Similar  to complete, but replaces the word to be completed with
              a single match from the list of possible completions.   Repeated
              execution  of  menu-complete  steps through the list of possible
              completions, inserting each match in turn.  At the  end  of  the
              list of completions, the bell is rung (subject to the setting of
              bell-style) and the original text is restored.  An argument of n
              moves  n  positions  forward  in the list of matches; a negative
              argument may be used to move backward through  the  list.   This
              command  is  intended  to  be  bound  to  TAB, but is unbound by
              default.
       delete-char-or-list
              Deletes the character under the cursor if not at  the  beginning
              or  end  of  the  line (like delete-char).  If at the end of the
              line, behaves identically to possible-completions.  This command
              is unbound by default.
       complete-filename (M-/)
              Attempt filename completion on the text before point.
       possible-filename-completions (C-x /)
              List the possible completions of the text before point, treating
              it as a filename.
       complete-username (M-~)
              Attempt completion on the text before point, treating  it  as  a
              username.
       possible-username-completions (C-x ~)
              List the possible completions of the text before point, treating
              it as a username.
       complete-variable (M-$)
              Attempt completion on the text before point, treating  it  as  a
              shell variable.
       possible-variable-completions (C-x $)
              List the possible completions of the text before point, treating
              it as a shell variable.
       complete-hostname (M-@)
              Attempt completion on the text before point, treating  it  as  a
              hostname.
       possible-hostname-completions (C-x @)
              List the possible completions of the text before point, treating
              it as a hostname.
       complete-command (M-!)
              Attempt completion on the text before point, treating  it  as  a
              command  name.   Command  completion  attempts to match the text
              against  aliases,  reserved  words,   shell   functions,   shell
              builtins, and finally executable filenames, in that order.
       possible-command-completions (C-x !)
              List the possible completions of the text before point, treating
              it as a command name.
       dynamic-complete-history (M-TAB)
              Attempt completion on the text before point, comparing the  text
              against  lines  from  the  history  list for possible completion
              matches.
       dabbrev-expand
              Attempt menu completion on the text before point, comparing  the
              text against lines from the history list for possible completion
              matches.
       complete-into-braces (M-{)
              Perform filename completion and  insert  the  list  of  possible
              completions  enclosed  within braces so the list is available to
              the shell (see Brace Expansion above).

   Keyboard Macros
       start-kbd-macro (C-x ()
              Begin saving the characters  typed  into  the  current  keyboard
              macro.
       end-kbd-macro (C-x ))
              Stop saving the characters typed into the current keyboard macro
              and store the definition.
       call-last-kbd-macro (C-x e)
              Re-execute the  last  keyboard  macro  defined,  by  making  the
              characters in the macro appear as if typed at the keyboard.

   Miscellaneous
       re-read-init-file (C-x C-r)
              Read  in  the  contents of the inputrc file, and incorporate any
              bindings or variable assignments found there.
       abort (C-g)
              Abort the current editing command and ring the  terminal’s  bell
              (subject to the setting of bell-style).
       do-uppercase-version (M-a, M-b, M-x, ...)
              If  the  metafied character x is lowercase, run the command that
              is bound to the corresponding uppercase character.
       prefix-meta (ESC)
              Metafy the next character typed.  ESC f is equivalent to Meta-f.
       undo (C-_, C-x C-u)
              Incremental undo, separately remembered for each line.
       revert-line (M-r)
              Undo  all changes made to this line.  This is like executing the
              undo command enough times to return  the  line  to  its  initial
              state.
       tilde-expand (M-&)
              Perform tilde expansion on the current word.
       set-mark (C-@, M-<space>)
              Set  the  mark to the point.  If a numeric argument is supplied,
              the mark is set to that position.
       exchange-point-and-mark (C-x C-x)
              Swap the point with the mark.  The current  cursor  position  is
              set  to the saved position, and the old cursor position is saved
              as the mark.
       character-search (C-])
              A character is read and point is moved to the next occurrence of
              that   character.    A  negative  count  searches  for  previous
              occurrences.
       character-search-backward (M-C-])
              A  character  is  read  and  point  is  moved  to  the  previous
              occurrence  of  that  character.   A negative count searches for
              subsequent occurrences.
       insert-comment (M-#)
              Without  a  numeric  argument,  the  value   of   the   readline
              comment-begin  variable  is  inserted  at  the  beginning of the
              current line.  If a numeric argument is supplied,  this  command
              acts  as  a  toggle:   if the characters at the beginning of the
              line do not match the  value  of  comment-begin,  the  value  is
              inserted,  otherwise the characters in comment-begin are deleted
              from the beginning of the line.  In either  case,  the  line  is
              accepted  as  if a newline had been typed.  The default value of
              comment-begin causes this command to make  the  current  line  a
              shell  comment.   If  a  numeric  argument  causes  the  comment
              character to be removed, the line will be executed by the shell.
       glob-complete-word (M-g)
              The  word  before  point  is  treated  as a pattern for pathname
              expansion, with an asterisk implicitly appended.   This  pattern
              is  used  to generate a list of matching file names for possible
              completions.
       glob-expand-word (C-x *)
              The word before point is  treated  as  a  pattern  for  pathname
              expansion,  and  the  list  of  matching file names is inserted,
              replacing the word.  If  a  numeric  argument  is  supplied,  an
              asterisk is appended before pathname expansion.
       glob-list-expansions (C-x g)
              The  list  of  expansions  that  would  have  been  generated by
              glob-expand-word is displayed, and the line is  redrawn.   If  a
              numeric  argument  is  supplied,  an asterisk is appended before
              pathname expansion.
       dump-functions
              Print all of  the  functions  and  their  key  bindings  to  the
              readline  output stream.  If a numeric argument is supplied, the
              output is formatted in such a way that it can be made part of an
              inputrc file.
       dump-variables
              Print all of the settable readline variables and their values to
              the readline output stream.  If a numeric argument is  supplied,
              the  output  is formatted in such a way that it can be made part
              of an inputrc file.
       dump-macros
              Print all of the readline key sequences bound to macros and  the
              strings  they  output.   If  a numeric argument is supplied, the
              output is formatted in such a way that it can be made part of an
              inputrc file.
       display-shell-version (C-x C-v)
              Display  version information about the current instance of bash.

   Programmable Completion
       When word completion is attempted for an  argument  to  a  command  for
       which  a  completion  specification (a compspec) has been defined using
       the  complete  builtin  (see  SHELL  BUILTIN   COMMANDS   below),   the
       programmable completion facilities are invoked.

       First,  the command name is identified.  If a compspec has been defined
       for that command, the compspec is used to generate the list of possible
       completions  for  the  word.  If the command word is a full pathname, a
       compspec for the full pathname is searched for first.  If  no  compspec
       is  found  for the full pathname, an attempt is made to find a compspec
       for the portion following the final slash.

       Once a compspec has been found, it is used  to  generate  the  list  of
       matching  words.   If  a  compspec  is  not  found,  the  default  bash
       completion as described above under Completing is performed.

       First, the actions specified by the compspec are  used.   Only  matches
       which  are prefixed by the word being completed are returned.  When the
       -f or -d option is used for filename or directory name completion,  the
       shell variable FIGNORE is used to filter the matches.

       Any  completions  specified  by  a filename expansion pattern to the -G
       option are generated next.  The words generated by the pattern need not
       match  the  word being completed.  The GLOBIGNORE shell variable is not
       used to filter the matches, but the FIGNORE variable is used.

       Next, the string  specified  as  the  argument  to  the  -W  option  is
       considered.   The string is first split using the characters in the IFS
       special variable as delimiters.  Shell quoting is honored.   Each  word
       is  then expanded using brace expansion, tilde expansion, parameter and
       variable expansion, command substitution, and arithmetic expansion,  as
       described above under EXPANSION.  The results are split using the rules
       described above under Word Splitting.  The results of the expansion are
       prefix-matched against the word being completed, and the matching words
       become the possible completions.

       After these matches have been generated, any shell function or  command
       specified  with  the -F and -C options is invoked.  When the command or
       function is invoked, the COMP_LINE, COMP_POINT, COMP_KEY, and COMP_TYPE
       variables are assigned values as described above under Shell Variables.
       If a shell function is being invoked,  the  COMP_WORDS  and  COMP_CWORD
       variables  are  also set.  When the function or command is invoked, the
       first argument is the name of the command  whose  arguments  are  being
       completed,  the  second  argument  is the word being completed, and the
       third argument is the word preceding the word being  completed  on  the
       current  command  line.   No  filtering  of  the  generated completions
       against the word being completed is performed; the function or  command
       has complete freedom in generating the matches.

       Any  function specified with -F is invoked first.  The function may use
       any of the shell facilities, including the  compgen  builtin  described
       below,  to  generate the matches.  It must put the possible completions
       in the COMPREPLY array variable.

       Next, any command specified  with  the  -C  option  is  invoked  in  an
       environment equivalent to command substitution.  It should print a list
       of completions, one per line, to the standard output.  Backslash may be
       used to escape a newline, if necessary.

       After  all  of  the  possible  completions  are  generated,  any filter
       specified with the -X option is applied to the list.  The filter  is  a
       pattern  as used for pathname expansion; a & in the pattern is replaced
       with the text of the word being completed.  A literal & may be  escaped
       with  a  backslash; the backslash is removed before attempting a match.
       Any completion that matches the pattern will be removed from the  list.
       A  leading  !  negates  the  pattern;  in  this case any completion not
       matching the pattern will be removed.

       Finally, any prefix and suffix specified with the -P and -S options are
       added to each member of the completion list, and the result is returned
       to the readline completion code as the list of possible completions.

       If the previously-applied actions do not generate any matches, and  the
       -o  dirnames  option  was  supplied  to  complete when the compspec was
       defined, directory name completion is attempted.

       If the -o plusdirs option was supplied to complete  when  the  compspec
       was defined, directory name completion is attempted and any matches are
       added to the results of the other actions.

       By default, if a compspec is found, whatever it generates  is  returned
       to  the  completion  code as the full set of possible completions.  The
       default bash completions are not attempted, and the readline default of
       filename  completion  is  disabled.   If  the -o bashdefault option was
       supplied to complete when the compspec was defined,  the  bash  default
       completions are attempted if the compspec generates no matches.  If the
       -o default option was  supplied  to  complete  when  the  compspec  was
       defined,  readline’s  default  completion  will  be  performed  if  the
       compspec (and, if attempted, the default bash completions) generate  no
       matches.

       When  a  compspec  indicates that directory name completion is desired,
       the programmable completion functions force readline to append a  slash
       to  completed names which are symbolic links to directories, subject to
       the value of the mark-directories readline variable, regardless of  the
       setting of the mark-symlinked-directories readline variable.

HISTORY

       When  the  -o  history  option to the set builtin is enabled, the shell
       provides access to the command history, the list of commands previously
       typed.   The  value  of  the HISTSIZE variable is used as the number of
       commands to save in a history list.  The  text  of  the  last  HISTSIZE
       commands  (default 500) is saved.  The shell stores each command in the
       history list prior to parameter and variable expansion  (see  EXPANSION
       above)  but after history expansion is performed, subject to the values
       of the shell variables HISTIGNORE and HISTCONTROL.

       On startup, the history is initialized  from  the  file  named  by  the
       variable  HISTFILE  (default  ~/.bash_history).   The file named by the
       value of HISTFILE is truncated, if necessary, to contain no  more  than
       the  number  of lines specified by the value of HISTFILESIZE.  When the
       history  file  is  read,  lines  beginning  with  the  history  comment
       character followed immediately by a digit are interpreted as timestamps
       for the  preceding  history  line.   These  timestamps  are  optionally
       displayed  depending on the value of the HISTTIMEFORMAT variable.  When
       an interactive shell exits, the last $HISTSIZE lines  are  copied  from
       the  history  list  to  $HISTFILE.   If  the histappend shell option is
       enabled (see the description of  shopt  under  SHELL  BUILTIN  COMMANDS
       below),  the  lines  are  appended  to  the history file, otherwise the
       history file is overwritten.  If HISTFILE is unset, or if  the  history
       file  is  unwritable,  the history is not saved.  If the HISTTIMEFORMAT
       variable is set, time stamps are written to the  history  file,  marked
       with  the  history  comment  character, so they may be preserved across
       shell sessions.  This uses the history comment character to distinguish
       timestamps  from  other  history  lines.  After saving the history, the
       history file is truncated to contain no more than  HISTFILESIZE  lines.
       If HISTFILESIZE is not set, no truncation is performed.

       The  builtin  command fc (see SHELL BUILTIN COMMANDS below) may be used
       to list or edit and re-execute a portion  of  the  history  list.   The
       history  builtin  may be used to display or modify the history list and
       manipulate the history file.  When using command-line  editing,  search
       commands  are available in each editing mode that provide access to the
       history list.

       The shell allows control over which commands are saved on  the  history
       list.  The HISTCONTROL and HISTIGNORE variables may be set to cause the
       shell to save only a subset of the commands entered.  The cmdhist shell
       option,  if enabled, causes the shell to attempt to save each line of a
       multi-line command in the same history entry, adding  semicolons  where
       necessary  to preserve syntactic correctness.  The lithist shell option
       causes the shell to save the command with embedded newlines instead  of
       semicolons.  See the description of the shopt builtin below under SHELL
       BUILTIN  COMMANDS  for  information  on  setting  and  unsetting  shell
       options.

HISTORY EXPANSION

       The  shell  supports a history expansion feature that is similar to the
       history expansion in csh.  This section describes what syntax  features
       are  available.   This  feature  is  enabled by default for interactive
       shells, and can be disabled using the +H  option  to  the  set  builtin
       command  (see SHELL BUILTIN COMMANDS below).  Non-interactive shells do
       not perform history expansion by default.

       History expansions introduce words from the history list into the input
       stream,  making  it  easy to repeat commands, insert the arguments to a
       previous command into the current input line, or fix errors in previous
       commands quickly.

       History  expansion  is  performed  immediately after a complete line is
       read, before the shell breaks it into words.  It  takes  place  in  two
       parts.   The  first is to determine which line from the history list to
       use during substitution.  The second is to select portions of that line
       for inclusion into the current one.  The line selected from the history
       is the event, and the portions of that line that  are  acted  upon  are
       words.   Various  modifiers  are  available  to manipulate the selected
       words.  The line is broken into words  in  the  same  fashion  as  when
       reading input, so that several metacharacter-separated words surrounded
       by quotes are considered one word.  History expansions  are  introduced
       by  the  appearance  of  the history expansion character, which is ! by
       default.  Only backslash (\) and single quotes can  quote  the  history
       expansion character.

       Several  characters  inhibit  history  expansion  if  found immediately
       following the history expansion character,  even  if  it  is  unquoted:
       space,  tab,  newline,  carriage  return,  and =.  If the extglob shell
       option is enabled, ( will also inhibit expansion.

       Several shell options settable with the shopt builtin may  be  used  to
       tailor  the  behavior  of  history  expansion.  If the histverify shell
       option is enabled (see the  description  of  the  shopt  builtin),  and
       readline  is  being  used,  history  substitutions  are not immediately
       passed to the shell parser.  Instead, the  expanded  line  is  reloaded
       into the readline editing buffer for further modification.  If readline
       is being used, and the histreedit shell option  is  enabled,  a  failed
       history  substitution will be reloaded into the readline editing buffer
       for correction.  The -p option to the history builtin  command  may  be
       used  to  see what a history expansion will do before using it.  The -s
       option to the history builtin may be used to add commands to the end of
       the  history  list  without  actually  executing them, so that they are
       available for subsequent recall.

       The shell allows control of the various characters used by the  history
       expansion mechanism (see the description of histchars above under Shell
       Variables).  The shell uses  the  history  comment  character  to  mark
       history timestamps when writing the history file.

   Event Designators
       An  event  designator  is  a  reference  to a command line entry in the
       history list.

       !      Start a history substitution, except when followed by  a  blank,
              newline,  carriage return, = or ( (when the extglob shell option
              is enabled using the shopt builtin).
       !n     Refer to command line n.
       !-n    Refer to the current command line minus n.
       !!     Refer to the previous command.  This is a synonym for ‘!-1’.
       !string
              Refer to the most recent command starting with string.
       !?string[?]
              Refer  to  the  most  recent  command  containing  string.   The
              trailing ? may be omitted if string is followed immediately by a
              newline.
       ^string1^string2^
              Quick substitution.  Repeat the last command, replacing  string1
              with  string2.   Equivalent  to  ‘‘!!:s/string1/string2/’’  (see
              Modifiers below).
       !#     The entire command line typed so far.

   Word Designators
       Word designators are used to select desired words from the event.  A  :
       separates  the event specification from the word designator.  It may be
       omitted if the word designator begins with a ^, $, *, -, or  %.   Words
       are  numbered from the beginning of the line, with the first word being
       denoted by  0  (zero).   Words  are  inserted  into  the  current  line
       separated by single spaces.

       0 (zero)
              The zeroth word.  For the shell, this is the command word.
       n      The nth word.
       ^      The first argument.  That is, word 1.
       $      The last argument.
       %      The word matched by the most recent ‘?string?’ search.
       x-y    A range of words; ‘-y’ abbreviates ‘0-y’.
       *      All  of  the words but the zeroth.  This is a synonym for ‘1-$’.
              It is not an error to use * if there is just  one  word  in  the
              event; the empty string is returned in that case.
       x*     Abbreviates x-$.
       x-     Abbreviates x-$ like x*, but omits the last word.

       If  a  word  designator is supplied without an event specification, the
       previous command is used as the event.

   Modifiers
       After the optional word designator, there may appear a sequence of  one
       or more of the following modifiers, each preceded by a ‘:’.

       h      Remove a trailing file name component, leaving only the head.
       t      Remove all leading file name components, leaving the tail.
       r      Remove a trailing suffix of the form .xxx, leaving the basename.
       e      Remove all but the trailing suffix.
       p      Print the new command but do not execute it.
       q      Quote the substituted words, escaping further substitutions.
       x      Quote the substituted words as with q, but break into  words  at
              blanks and newlines.
       s/old/new/
              Substitute  new  for  the  first  occurrence of old in the event
              line.  Any delimiter can be used  in  place  of  /.   The  final
              delimiter  is  optional if it is the last character of the event
              line.  The delimiter may be quoted in old and new with a  single
              backslash.   If  &  appears  in  new,  it is replaced by old.  A
              single backslash will quote the &.  If old is null, it is set to
              the   last   old   substituted,   or,  if  no  previous  history
              substitutions took place,  the  last  string  in  a  !?string[?]
              search.
       &      Repeat the previous substitution.
       g      Cause changes to be applied over the entire event line.  This is
              used in conjunction with ‘:s’ (e.g.,  ‘:gs/old/new/’)  or  ‘:&’.
              If  used with ‘:s’, any delimiter can be used in place of /, and
              the final delimiter is optional if it is the last  character  of
              the event line.  An a may be used as a synonym for g.
       G      Apply  the following ‘s’ modifier once to each word in the event
              line.

SHELL BUILTIN COMMANDS

       Unless otherwise noted, each builtin command documented in this section
       as accepting options preceded by - accepts -- to signify the end of the
       options.  For example, the :, true, false, and  test  builtins  do  not
       accept options.
       : [arguments]
              No  effect;  the command does nothing beyond expanding arguments
              and performing any specified redirections.  A zero exit code  is
              returned.

        .  filename [arguments]
       source filename [arguments]
              Read  and  execute  commands  from filename in the current shell
              environment and return the  exit  status  of  the  last  command
              executed  from  filename.  If filename does not contain a slash,
              file names in PATH are used to  find  the  directory  containing
              filename.  The file searched for in PATH need not be executable.
              When bash is  not  in  posix  mode,  the  current  directory  is
              searched  if no file is found in PATH.  If the sourcepath option
              to the shopt builtin command is turned  off,  the  PATH  is  not
              searched.   If  any  arguments  are  supplied,  they  become the
              positional parameters when filename is executed.  Otherwise  the
              positional  parameters  are unchanged.  The return status is the
              status of the last command exited within the  script  (0  if  no
              commands  are  executed),  and false if filename is not found or
              cannot be read.

       alias [-p] [name[=value] ...]
              Alias with no arguments or with the -p option prints the list of
              aliases  in  the form alias name=value on standard output.  When
              arguments are supplied, an alias is defined for each name  whose
              value is given.  A trailing space in  value causes the next word
              to be checked for alias substitution when the alias is expanded.
              For  each  name  in  the  argument  list  for  which no value is
              supplied, the name and value of the  alias  is  printed.   Alias
              returns  true unless a name is given for which no alias has been
              defined.

       bg [jobspec ...]
              Resume each suspended job jobspec in the background,  as  if  it
              had been started with &.  If jobspec is not present, the shell’s
              notion of the current job is used.  bg jobspec returns 0  unless
              run  when  job control is disabled or, when run with job control
              enabled, any specified jobspec was  not  found  or  was  started
              without job control.

       bind [-m keymap] [-lpsvPSV]
       bind [-m keymap] [-q function] [-u function] [-r keyseq]
       bind [-m keymap] -f filename
       bind [-m keymap] -x keyseq:shell-command
       bind [-m keymap] keyseq:function-name
       bind readline-command
              Display  current  readline key and function bindings, bind a key
              sequence to a readline function or  macro,  or  set  a  readline
              variable.   Each  non-option  argument  is a command as it would
              appear in .inputrc, but each binding or command must  be  passed
              as  a  separate argument; e.g., ’"\C-x\C-r": re-read-init-file’.
              Options, if supplied, have the following meanings:
              -m keymap
                     Use keymap as the keymap to be affected by the subsequent
                     bindings.     Acceptable    keymap   names   are   emacs,
                     emacs-standard,  emacs-meta,  emacs-ctlx,  vi,   vi-move,
                     vi-command,   and   vi-insert.    vi   is  equivalent  to
                     vi-command; emacs is equivalent to emacs-standard.
              -l     List the names of all readline functions.
              -p     Display readline function names and bindings  in  such  a
                     way that they can be re-read.
              -P     List current readline function names and bindings.
              -s     Display  readline  key  sequences bound to macros and the
                     strings they output in such a way that they  can  be  re-
                     read.
              -S     Display  readline  key  sequences bound to macros and the
                     strings they output.
              -v     Display readline variable names and values in such a  way
                     that they can be re-read.
              -V     List current readline variable names and values.
              -f filename
                     Read key bindings from filename.
              -q function
                     Query about which keys invoke the named function.
              -u function
                     Unbind all keys bound to the named function.
              -r keyseq
                     Remove any current binding for keyseq.
              -x keyseq:shell-command
                     Cause  shell-command  to  be  executed whenever keyseq is
                     entered.  When shell-command is executed, the shell  sets
                     the   READLINE_LINE  variable  to  the  contents  of  the
                     readline line buffer and the READLINE_POINT  variable  to
                     the  current  location  of  the  insertion point.  If the
                     executed command changes the value  of  READLINE_LINE  or
                     READLINE_POINT, those new values will be reflected in the
                     editing state.

              The return value is 0 unless an unrecognized option is given  or
              an error occurred.

       break [n]
              Exit  from  within a for, while, until, or select loop.  If n is
              specified, break n levels.  n must be ≥ 1.  If n is greater than
              the  number  of enclosing loops, all enclosing loops are exited.
              The return value is 0 unless n is not greater than or  equal  to
              1.

       builtin shell-builtin [arguments]
              Execute  the  specified shell builtin, passing it arguments, and
              return its exit status.  This is useful when defining a function
              whose  name  is  the  same  as  a  shell  builtin, retaining the
              functionality of  the  builtin  within  the  function.   The  cd
              builtin  is  commonly  redefined this way.  The return status is
              false if shell-builtin is not a shell builtin command.

       caller [expr]
              Returns the context of  any  active  subroutine  call  (a  shell
              function  or  a  script  executed with the . or source builtins.
              Without  expr,  caller  displays  the  line  number  and  source
              filename  of  the  current  subroutine  call.  If a non-negative
              integer is supplied as expr, caller displays  the  line  number,
              subroutine  name, and source file corresponding to that position
              in the current execution call stack.  This extra information may
              be used, for example, to print a stack trace.  The current frame
              is frame 0.  The return value is  0  unless  the  shell  is  not
              executing  a  subroutine  call  or expr does not correspond to a
              valid position in the call stack.

       cd [-L|-P] [dir]
              Change the current directory to dir.  The variable HOME  is  the
              default  dir.   The  variable CDPATH defines the search path for
              the directory containing dir.  Alternative  directory  names  in
              CDPATH  are  separated by a colon (:).  A null directory name in
              CDPATH is the same as the current directory,  i.e.,  ‘‘.’’.   If
              dir  begins  with  a  slash (/), then CDPATH is not used. The -P
              option says to use the physical directory structure  instead  of
              following  symbolic  links  (see  also  the -P option to the set
              builtin command); the -L option  forces  symbolic  links  to  be
              followed.  An argument of - is equivalent to $OLDPWD.  If a non-
              empty directory name from CDPATH is used, or if - is  the  first
              argument,  and  the directory change is successful, the absolute
              pathname of the new working directory is written to the standard
              output.    The  return  value  is  true  if  the  directory  was
              successfully changed; false otherwise.

       command [-pVv] command [arg ...]
              Run command with args  suppressing  the  normal  shell  function
              lookup.  Only builtin commands or commands found in the PATH are
              executed.  If the -p option is given, the search for command  is
              performed  using  a default value for PATH that is guaranteed to
              find all of the standard utilities.  If  either  the  -V  or  -v
              option is supplied, a description of command is printed.  The -v
              option causes a single word indicating the command or file  name
              used to invoke command to be displayed; the -V option produces a
              more verbose description.  If the -V or -v option  is  supplied,
              the  exit  status  is  0 if command was found, and 1 if not.  If
              neither option is supplied and  an  error  occurred  or  command
              cannot  be  found,  the exit status is 127.  Otherwise, the exit
              status of the command builtin is the exit status of command.

       compgen [option] [word]
              Generate possible completion matches for word according  to  the
              options,  which  may  be  any  option  accepted  by the complete
              builtin with the exception of -p and -r, and write  the  matches
              to  the  standard  output.  When using the -F or -C options, the
              various shell  variables  set  by  the  programmable  completion
              facilities, while available, will not have useful values.

              The  matches  will  be  generated  in  the  same  way  as if the
              programmable completion code had generated them directly from  a
              completion  specification  with  the  same  flags.   If  word is
              specified,  only  those  completions  matching  word   will   be
              displayed.

              The  return  value is true unless an invalid option is supplied,
              or no matches were generated.

       complete [-abcdefgjksuv] [-o comp-option] [-E] [-A action] [-G globpat]
       [-W wordlist] [-F function] [-C command]
              [-X filterpat] [-P prefix] [-S suffix] name [name ...]
       complete -pr [-E] [name ...]
              Specify how arguments to each name should be completed.  If  the
              -p  option  is supplied, or if no options are supplied, existing
              completion specifications are printed in a way that allows  them
              to  be  reused  as  input.   The  -r option removes a completion
              specification for each name, or, if no names are  supplied,  all
              completion  specifications.   The  -E  option indicates that the
              remaining options and actions should apply to ‘‘empty’’  command
              completion; that is, completion attempted on a blank line.

              The  process  of  applying  these completion specifications when
              word  completion  is  attempted   is   described   above   under
              Programmable Completion.

              Other  options,  if specified, have the following meanings.  The
              arguments to the -G, -W, and -X options (and, if necessary,  the
              -P  and  -S  options)  should  be  quoted  to  protect them from
              expansion before the complete builtin is invoked.
              -o comp-option
                      The  comp-option  controls  several   aspects   of   the
                      compspec’s  behavior  beyond  the  simple  generation of
                      completions.  comp-option may be one of:
                      bashdefault
                              Perform the rest of the default bash completions
                              if the compspec generates no matches.
                      default Use  readline’s  default  filename completion if
                              the compspec generates no matches.
                      dirnames
                              Perform  directory  name   completion   if   the
                              compspec generates no matches.
                      filenames
                              Tell   readline   that  the  compspec  generates
                              filenames,    so    it    can    perform     any
                              filename-specific   processing  (like  adding  a
                              slash  to  directory  names,   quoting   special
                              characters,  or  suppressing  trailing  spaces).
                              Intended to be used with shell functions.
                      nospace Tell  readline  not  to  append  a  space   (the
                              default)  to  words  completed at the end of the
                              line.
                      plusdirs
                              After any matches defined by  the  compspec  are
                              generated,    directory   name   completion   is
                              attempted and  any  matches  are  added  to  the
                              results of the other actions.
              -A action
                      The  action  may  be  one of the following to generate a
                      list of possible completions:
                      alias   Alias names.  May also be specified as -a.
                      arrayvar
                              Array variable names.
                      binding Readline key binding names.
                      builtin Names of shell builtin commands.   May  also  be
                              specified as -b.
                      command Command names.  May also be specified as -c.
                      directory
                              Directory names.  May also be specified as -d.
                      disabled
                              Names of disabled shell builtins.
                      enabled Names of enabled shell builtins.
                      export  Names  of exported shell variables.  May also be
                              specified as -e.
                      file    File names.  May also be specified as -f.
                      function
                              Names of shell functions.
                      group   Group names.  May also be specified as -g.
                      helptopic
                              Help topics as accepted by the help builtin.
                      hostname
                              Hostnames, as taken from the file  specified  by
                              the HOSTFILE shell variable.
                      job     Job  names,  if job control is active.  May also
                              be specified as -j.
                      keyword Shell reserved words.  May also be specified  as
                              -k.
                      running Names of running jobs, if job control is active.
                      service Service names.  May also be specified as -s.
                      setopt  Valid arguments for the -o  option  to  the  set
                              builtin.
                      shopt   Shell  option  names  as  accepted  by the shopt
                              builtin.
                      signal  Signal names.
                      stopped Names of stopped jobs, if job control is active.
                      user    User names.  May also be specified as -u.
                      variable
                              Names  of  all  shell  variables.   May  also be
                              specified as -v.
              -G globpat
                      The filename expansion pattern globpat  is  expanded  to
                      generate the possible completions.
              -W wordlist
                      The  wordlist  is  split using the characters in the IFS
                      special variable as delimiters, and each resultant  word
                      is  expanded.   The possible completions are the members
                      of  the  resultant  list  which  match  the  word  being
                      completed.
              -C command
                      command  is  executed in a subshell environment, and its
                      output is used as the possible completions.
              -F function
                      The shell function function is executed in  the  current
                      shell  environment.   When  it  finishes,  the  possible
                      completions  are  retrieved  from  the  value   of   the
                      COMPREPLY array variable.
              -X filterpat
                      filterpat  is  a pattern as used for filename expansion.
                      It is  applied  to  the  list  of  possible  completions
                      generated  by  the  preceding options and arguments, and
                      each completion matching filterpat is removed  from  the
                      list.   A leading ! in filterpat negates the pattern; in
                      this case, any  completion  not  matching  filterpat  is
                      removed.
              -P prefix
                      prefix  is  added  at  the  beginning  of  each possible
                      completion after all other options have been applied.
              -S suffix
                      suffix is appended to each possible completion after all
                      other options have been applied.

              The  return  value is true unless an invalid option is supplied,
              an option other than  -p  or  -r  is  supplied  without  a  name
              argument,   an   attempt   is   made   to  remove  a  completion
              specification for a name for which no specification  exists,  or
              an error occurs adding a completion specification.

       compopt [-o option] [+o option] [name]
              Modify  completion  options  for  each  name  according  to  the
              options, or for the currently-execution completion if  no  names
              are  supplied.   If no options are given, display the completion
              options for each name or the current completion.   The  possible
              values  of  option  are  those  valid  for  the complete builtin
              described above.

       The return value is true unless  an  invalid  option  is  supplied,  an
       attempt  is  made  to  modify  the  options  for  a  name  for which no
       completion specification exists, or an output error occurs.

       continue [n]
              Resume the next iteration of the enclosing for, while, until, or
              select  loop.   If  n  is specified, resume at the nth enclosing
              loop.  n must be ≥ 1.  If  n  is  greater  than  the  number  of
              enclosing  loops,  the  last  enclosing  loop (the ‘‘top-level’’
              loop) is resumed.  The return value is 0 unless n is not greater
              than or equal to 1.

       declare [-aAfFilrtux] [-p] [name[=value] ...]
       typeset [-aAfFilrtux] [-p] [name[=value] ...]
              Declare  variables and/or give them attributes.  If no names are
              given then display the values of variables.  The -p option  will
              display the attributes and values of each name.  When -p is used
              with name arguments, additional options are ignored.  When -p is
              supplied  without name arguments, it will display the attributes
              and values of all variables having the attributes  specified  by
              the  additional  options.  If no other options are supplied with
              -p, declare will display the attributes and values of all  shell
              variables.   The  -f  option  will restrict the display to shell
              functions.  The -F  option  inhibits  the  display  of  function
              definitions;  only the function name and attributes are printed.
              If the extdebug shell option is enabled using shopt, the  source
              file  name  and  line  number  where the function is defined are
              displayed as well.  The -F option  implies  -f.   The  following
              options  can  be  used  to restrict output to variables with the
              specified attribute or to give variables attributes:
              -a     Each name  is  an  indexed  array  variable  (see  Arrays
                     above).
              -A     Each  name  is  an associative array variable (see Arrays
                     above).
              -f     Use function names only.
              -i     The  variable  is  treated  as  an  integer;   arithmetic
                     evaluation (see ARITHMETIC EVALUATION ) is performed when
                     the variable is assigned a value.
              -l     When the variable is assigned  a  value,  all  upper-case
                     characters  are  converted to lower-case.  The upper-case
                     attribute is disabled.
              -r     Make names readonly.  These names cannot then be assigned
                     values by subsequent assignment statements or unset.
              -t     Give  each  name  the  trace attribute.  Traced functions
                     inherit the DEBUG  and  RETURN  traps  from  the  calling
                     shell.   The  trace  attribute has no special meaning for
                     variables.
              -u     When the variable is assigned  a  value,  all  lower-case
                     characters  are  converted to upper-case.  The lower-case
                     attribute is disabled.
              -x     Mark names for export  to  subsequent  commands  via  the
                     environment.

              Using  ‘+’  instead of ‘-’ turns off the attribute instead, with
              the exceptions that +a may not  be  used  to  destroy  an  array
              variable  and  +r  will not remove the readonly attribute.  When
              used in a function, makes each name local,  as  with  the  local
              command.  If a variable name is followed by =value, the value of
              the variable is set to value.  The return value is 0  unless  an
              invalid  option  is  encountered, an attempt is made to define a
              function using ‘‘-f foo=bar’’, an attempt is made  to  assign  a
              value  to  a  readonly  variable, an attempt is made to assign a
              value to an array variable without using the compound assignment
              syntax (see Arrays above), one of the names is not a valid shell
              variable name, an attempt is made to turn  off  readonly  status
              for  a  readonly  variable, an attempt is made to turn off array
              status for an array variable, or an attempt is made to display a
              non-existent function with -f.

       dirs [+n] [-n] [-cplv]
              Without  options,  displays  the  list  of  currently remembered
              directories.  The default display  is  on  a  single  line  with
              directory  names  separated by spaces.  Directories are added to
              the list with  the  pushd  command;  the  popd  command  removes
              entries from the list.
              +n     Displays the nth entry counting from the left of the list
                     shown by dirs when invoked without options, starting with
                     zero.
              -n     Displays  the  nth  entry  counting from the right of the
                     list shown by dirs when invoked without options, starting
                     with zero.
              -c     Clears  the  directory  stack  by  deleting  all  of  the
                     entries.
              -l     Produces a longer listing;  the  default  listing  format
                     uses a tilde to denote the home directory.
              -p     Print the directory stack with one entry per line.
              -v     Print  the  directory  stack  with  one  entry  per line,
                     prefixing each entry with its index in the stack.

              The return value is 0 unless an invalid option is supplied or  n
              indexes beyond the end of the directory stack.

       disown [-ar] [-h] [jobspec ...]
              Without  options,  each  jobspec  is  removed  from the table of
              active jobs.  If jobspec is not present, and neither -a  nor  -r
              is  supplied, the shells notion of the current job is used.  If
              the -h option is given, each jobspec is  not  removed  from  the
              table,  but  is  marked so that SIGHUP is not sent to the job if
              the shell receives a SIGHUP.  If  no  jobspec  is  present,  and
              neither the -a nor the -r option is supplied, the current job is
              used.  If no jobspec is supplied, the -a option means to  remove
              or  mark  all  jobs;  the  -r  option without a jobspec argument
              restricts operation to running jobs.   The  return  value  is  0
              unless a jobspec does not specify a valid job.

       echo [-neE] [arg ...]
              Output  the  args,  separated  by spaces, followed by a newline.
              The return status is always 0.  If -n is specified, the trailing
              newline   is   suppressed.    If   the   -e   option  is  given,
              interpretation of the following backslash-escaped characters  is
              enabled.   The  -E  option  disables the interpretation of these
              escape characters, even on systems where they are interpreted by
              default.   The  xpg_echo shell option may be used to dynamically
              determine whether or not echo expands these escape characters by
              default.  echo does not interpret -- to mean the end of options.
              echo interprets the following escape sequences:
              \a     alert (bell)
              \b     backspace
              \c     suppress further output
              \e     an escape character
              \f     form feed
              \n     new line
              \r     carriage return
              \t     horizontal tab
              \v     vertical tab
              \\     backslash
              \0nnn  the eight-bit character whose value is  the  octal  value
                     nnn (zero to three octal digits)
              \xHH   the  eight-bit  character  whose value is the hexadecimal
                     value HH (one or two hex digits)

       enable [-a] [-dnps] [-f filename] [name ...]
              Enable and disable builtin shell commands.  Disabling a  builtin
              allows a disk command which has the same name as a shell builtin
              to be executed without specifying a full pathname,  even  though
              the  shell  normally searches for builtins before disk commands.
              If -n is used, each  name  is  disabled;  otherwise,  names  are
              enabled.  For example, to use the test binary found via the PATH
              instead of the shell builtin version, run  ‘‘enable  -n  test’’.
              The  -f  option  means to load the new builtin command name from
              shared object filename, on systems that support dynamic loading.
              The  -d  option will delete a builtin previously loaded with -f.
              If no name arguments are given, or if the -p option is supplied,
              a  list  of  shell  builtins  is  printed.  With no other option
              arguments, the list consists of all enabled shell builtins.   If
              -n  is  supplied,  only disabled builtins are printed.  If -a is
              supplied, the  list  printed  includes  all  builtins,  with  an
              indication  of  whether  or  not  each  is  enabled.   If  -s is
              supplied,  the  output  is  restricted  to  the  POSIX   special
              builtins.   The  return  value is 0 unless a name is not a shell
              builtin or there is an error loading a new builtin from a shared
              object.

       eval [arg ...]
              The  args  are  read  and  concatenated  together  into a single
              command.  This command is then read and executed by  the  shell,
              and  its exit status is returned as the value of eval.  If there
              are no args, or only null arguments, eval returns 0.

       exec [-cl] [-a name] [command [arguments]]
              If command is specified, it replaces the shell.  No new  process
              is  created.  The arguments become the arguments to command.  If
              the -l option is supplied,  the  shell  places  a  dash  at  the
              beginning  of  the  zeroth  argument passed to command.  This is
              what login(1) does.  The -c option causes command to be executed
              with  an empty environment.  If -a is supplied, the shell passes
              name as the zeroth argument to the executed command.  If command
              cannot  be  executed  for  some  reason, a non-interactive shell
              exits, unless the shell option execfail  is  enabled,  in  which
              case  it  returns failure.  An interactive shell returns failure
              if the file cannot be executed.  If command  is  not  specified,
              any  redirections  take  effect  in  the  current shell, and the
              return status is 0.  If there is a redirection error, the return
              status is 1.

       exit [n]
              Cause  the  shell  to exit with a status of n.  If n is omitted,
              the exit status is that of the last command executed.  A trap on
              EXIT is executed before the shell terminates.

       export [-fn] [name[=word]] ...
       export -p
              The  supplied  names  are  marked  for  automatic  export to the
              environment of subsequently executed commands.  If the -f option
              is  given, the names refer to functions.  If no names are given,
              or if the -p option is supplied, a list of all  names  that  are
              exported  in  this  shell  is printed.  The -n option causes the
              export property to be removed from each  name.   If  a  variable
              name  is  followed by =word, the value of the variable is set to
              word.  export returns an exit status  of  0  unless  an  invalid
              option  is  encountered,  one  of the names is not a valid shell
              variable name, or -f is supplied with  a  name  that  is  not  a
              function.

       fc [-e ename] [-lnr] [first] [last]
       fc -s [pat=rep] [cmd]
              Fix  Command.  In the first form, a range of commands from first
              to last is selected from the history list.  First and  last  may
              be  specified  as a string (to locate the last command beginning
              with that string) or as a number  (an  index  into  the  history
              list,  where  a  negative  number  is used as an offset from the
              current command number).  If last is not specified it is set  to
              the  current  command  for listing (so that ‘‘fc -l -10’’ prints
              the last 10 commands) and to first otherwise.  If first  is  not
              specified  it is set to the previous command for editing and -16
              for listing.

              The -n option suppresses the command numbers when listing.   The
              -r  option reverses the order of the commands.  If the -l option
              is  given,  the  commands  are  listed   on   standard   output.
              Otherwise,  the  editor  given  by  ename  is  invoked on a file
              containing those commands.  If ename is not given, the value  of
              the  FCEDIT  variable is used, and the value of EDITOR if FCEDIT
              is not set.  If neither variable  is  set,  vi  is  used.   When
              editing   is  complete,  the  edited  commands  are  echoed  and
              executed.

              In the second form, command is re-executed after  each  instance
              of  pat  is replaced by rep.  A useful alias to use with this is
              ‘‘r="fc -s"’’, so that typing ‘‘r cc’’  runs  the  last  command
              beginning  with  ‘‘cc’’  and  typing  ‘‘r’’ re-executes the last
              command.

              If the first form is used, the  return  value  is  0  unless  an
              invalid  option  is encountered or first or last specify history
              lines out of range.  If the -e option is  supplied,  the  return
              value is the value of the last command executed or failure if an
              error occurs with the temporary file of commands.  If the second
              form  is  used,  the  return  status  is that of the command re-
              executed, unless cmd does not specify a valid history  line,  in
              which case fc returns failure.

       fg [jobspec]
              Resume  jobspec  in the foreground, and make it the current job.
              If jobspec is not present, the shell’s notion of the current job
              is  used.   The  return value is that of the command placed into
              the foreground, or failure if run when job control  is  disabled
              or,  when  run  with  job  control  enabled, if jobspec does not
              specify a valid job or jobspec specifies a job that was  started
              without job control.

       getopts optstring name [args]
              getopts   is  used  by  shell  procedures  to  parse  positional
              parameters.  optstring contains  the  option  characters  to  be
              recognized; if a character is followed by a colon, the option is
              expected to have an argument, which should be separated from  it
              by  white space.  The colon and question mark characters may not
              be used as option characters.  Each time it is invoked,  getopts
              places  the next option in the shell variable name, initializing
              name if it does not exist, and the index of the next argument to
              be processed into the variable OPTIND.  OPTIND is initialized to
              1 each time the shell or a shell script  is  invoked.   When  an
              option  requires  an argument, getopts places that argument into
              the  variable  OPTARG.   The  shell  does   not   reset   OPTIND
              automatically;  it must be manually reset between multiple calls
              to getopts within the same shell invocation  if  a  new  set  of
              parameters is to be used.

              When  the  end  of  options is encountered, getopts exits with a
              return value greater than zero.  OPTIND is set to the  index  of
              the first non-option argument, and name is set to ?.

              getopts  normally  parses the positional parameters, but if more
              arguments are given in args, getopts parses those instead.

              getopts can report errors in two ways.  If the  first  character
              of  optstring  is  a  colon, silent error reporting is used.  In
              normal operation diagnostic messages are  printed  when  invalid
              options  or  missing  option  arguments are encountered.  If the
              variable  OPTERR  is  set  to  0,  no  error  messages  will  be
              displayed,  even  if  the  first character of optstring is not a
              colon.

              If an invalid option is seen, getopts places ? into name and, if
              not  silent,  prints  an  error  message  and unsets OPTARG.  If
              getopts is silent, the  option  character  found  is  placed  in
              OPTARG and no diagnostic message is printed.

              If  a required argument is not found, and getopts is not silent,
              a question mark (?) is placed in name, OPTARG is  unset,  and  a
              diagnostic  message  is  printed.   If getopts is silent, then a
              colon (:) is placed in name and OPTARG  is  set  to  the  option
              character found.

              getopts  returns true if an option, specified or unspecified, is
              found.  It returns false if the end of options is encountered or
              an error occurs.

       hash [-lr] [-p filename] [-dt] [name]
              For  each  name, the full file name of the command is determined
              by searching the directories in $PATH and remembered.  If the -p
              option is supplied, no path search is performed, and filename is
              used as the full file name of the command.  The -r option causes
              the  shell  to  forget  all remembered locations.  The -d option
              causes the shell to forget the remembered location of each name.
              If  the  -t  option is supplied, the full pathname to which each
              name corresponds is printed.  If  multiple  name  arguments  are
              supplied  with  -t,  the  name is printed before the hashed full
              pathname.  The -l option causes output  to  be  displayed  in  a
              format  that may be reused as input.  If no arguments are given,
              or if only -l is supplied, information about remembered commands
              is  printed.   The  return  status  is true unless a name is not
              found or an invalid option is supplied.

       help [-dms] [pattern]
              Display helpful information about builtin commands.  If  pattern
              is  specified, help gives detailed help on all commands matching
              pattern; otherwise help for all the builtins and  shell  control
              structures is printed.
              -d     Display a short description of each pattern
               -m    Display the description of each pattern in a manpage-like
                     format
              -s     Display only a short usage synopsis for each pattern
       The return status is 0 unless no command matches pattern.

       history [n]
       history -c
       history -d offset
       history -anrw [filename]
       history -p arg [arg ...]
       history -s arg [arg ...]
              With no options, display the  command  history  list  with  line
              numbers.  Lines listed with a * have been modified.  An argument
              of n lists only  the  last  n  lines.   If  the  shell  variable
              HISTTIMEFORMAT  is  set  and  not  null,  it is used as a format
              string for strftime(3) to display the time stamp associated with
              each  displayed  history entry.  No intervening blank is printed
              between the formatted time  stamp  and  the  history  line.   If
              filename  is  supplied,  it  is  used as the name of the history
              file; if not, the  value  of  HISTFILE  is  used.   Options,  if
              supplied, have the following meanings:
              -c     Clear the history list by deleting all the entries.
              -d offset
                     Delete the history entry at position offset.
              -a     Append  the  ‘‘new’’ history lines (history lines entered
                     since the beginning of the current bash session)  to  the
                     history file.
              -n     Read  the history lines not already read from the history
                     file into the current  history  list.   These  are  lines
                     appended  to  the history file since the beginning of the
                     current bash session.
              -r     Read the contents of the history file and use them as the
                     current history.
              -w     Write   the   current   history   to  the  history  file,
                     overwriting the history file’s contents.
              -p     Perform history substitution on the  following  args  and
                     display  the  result  on  the  standard output.  Does not
                     store the results in the history list.  Each arg must  be
                     quoted to disable normal history expansion.
              -s     Store  the  args  in  the history list as a single entry.
                     The last command in the history list  is  removed  before
                     the args are added.

              If  the  HISTTIMEFORMAT  is  set,  the  time  stamp  information
              associated with each history entry is  written  to  the  history
              file,  marked  with  the  history  comment  character.  When the
              history file is read, lines beginning with the  history  comment
              character  followed  immediately  by  a digit are interpreted as
              timestamps for the previous history line.  The return value is 0
              unless  an  invalid option is encountered, an error occurs while
              reading or writing  the  history  file,  an  invalid  offset  is
              supplied as an argument to -d, or the history expansion supplied
              as an argument to -p fails.

       jobs [-lnprs] [ jobspec ... ]
       jobs -x command [ args ... ]
              The first form lists the active  jobs.   The  options  have  the
              following meanings:
              -l     List process IDs in addition to the normal information.
              -p     List  only  the  process  ID  of  the job’s process group
                     leader.
              -n     Display information only about  jobs  that  have  changed
                     status  since the user was last notified of their status.
              -r     Restrict output to running jobs.
              -s     Restrict output to stopped jobs.

              If jobspec is given, output is restricted to  information  about
              that  job.   The  return status is 0 unless an invalid option is
              encountered or an invalid jobspec is supplied.

              If the -x option is supplied, jobs replaces any jobspec found in
              command  or  args  with  the corresponding process group ID, and
              executes command passing it args, returning its exit status.

       kill [-s sigspec | -n signum | -sigspec] [pid | jobspec] ...
       kill -l [sigspec | exit_status]
              Send the signal named by sigspec  or  signum  to  the  processes
              named  by  pid or jobspec.  sigspec is either a case-insensitive
              signal name such as SIGKILL (with or without the SIG prefix)  or
              a  signal  number; signum is a signal number.  If sigspec is not
              present, then SIGTERM is assumed.  An argument of -l  lists  the
              signal  names.   If any arguments are supplied when -l is given,
              the names of the signals  corresponding  to  the  arguments  are
              listed, and the return status is 0.  The exit_status argument to
              -l is a number specifying either a signal  number  or  the  exit
              status  of  a process terminated by a signal.  kill returns true
              if at least one signal was successfully sent,  or  false  if  an
              error occurs or an invalid option is encountered.

       let arg [arg ...]
              Each  arg  is  an  arithmetic  expression  to  be evaluated (see
              ARITHMETIC EVALUATION).  If the last arg  evaluates  to  0,  let
              returns 1; 0 is returned otherwise.

       local [option] [name[=value] ...]
              For  each  argument, a local variable named name is created, and
              assigned value.  The option can be any of the  options  accepted
              by declare.  When local is used within a function, it causes the
              variable name  to  have  a  visible  scope  restricted  to  that
              function  and  its  children.   With no operands, local writes a
              list of local variables to the standard output.  It is an  error
              to use local when not within a function.  The return status is 0
              unless local is used outside a  function,  an  invalid  name  is
              supplied, or name is a readonly variable.

       logout Exit a login shell.

       mapfile  [-n  count]  [-O origin] [-s count] [-t] [-u fd] [-C callback]
       [-c quantum] [array]
       readarray  [-n count] [-O origin] [-s count] [-t] [-u fd] [-C callback]
       [-c quantum] [array]
              Read lines from the standard input into array variable array, or
              from file descriptor fd if  the  -u  option  is  supplied.   The
              variable  MAPFILE  is  the default array.  Options, if supplied,
              have the following meanings:
              -n     Copy at most count lines.  If count is 0, all  lines  are
                     copied.
              -O     Begin  assigning  to  array at index origin.  The default
                     index is 0.
              -s     Discard the first count lines read.
              -t     Remove a trailing line from each line read.
              -u     Read  lines  from  file  descriptor  fd  instead  of  the
                     standard input.
              -C     Evaluate  callback each time quantum lines are read.  The
                     -c option specifies quantum.
              -c     Specify the number of lines read  between  each  call  to
                     callback.

              If  -C  is  specified  without  -c, the default quantum is 5000.
              When callback is evaluated, it is supplied the index of the next
              array   element  to  be  assigned  as  an  additional  argument.
              callback is evaluated after the line  is  read  but  before  the
              array element is assigned.

              If  not  supplied  with  an  explicit origin, mapfile will clear
              array before assigning to it.

              mapfile returns successfully unless an invalid option or  option
              argument is supplied, or array is invalid or unassignable.

       popd [-n] [+n] [-n]
              Removes  entries  from  the directory stack.  With no arguments,
              removes the top directory from the stack, and performs a  cd  to
              the  new  top  directory.   Arguments,  if  supplied,  have  the
              following meanings:
              -n     Suppresses the normal change of directory  when  removing
                     directories  from  the  stack,  so that only the stack is
                     manipulated.
              +n     Removes the nth entry counting from the left of the  list
                     shown  by  dirs, starting with zero.  For example: ‘‘popd
                     +0’’ removes the first directory, ‘‘popd +1’’ the second.
              -n     Removes the nth entry counting from the right of the list
                     shown by dirs, starting with zero.  For  example:  ‘‘popd
                     -0’’  removes the last directory, ‘‘popd -1’’ the next to
                     last.

              If the popd command is successful, a dirs is performed as  well,
              and  the  return  status is 0.  popd returns false if an invalid
              option is encountered, the directory  stack  is  empty,  a  non-
              existent  directory  stack  entry is specified, or the directory
              change fails.

       printf [-v var] format [arguments]
              Write the formatted arguments to the standard output  under  the
              control  of  the format.  The format is a character string which
              contains three types of objects:  plain  characters,  which  are
              simply  copied  to  standard output, character escape sequences,
              which are converted and  copied  to  the  standard  output,  and
              format specifications, each of which causes printing of the next
              successive argument.  In  addition  to  the  standard  printf(1)
              formats,  %b  causes printf to expand backslash escape sequences
              in the corresponding argument (except that \c terminates output,
              backslashes in \', \", and \? are not removed, and octal escapes
              beginning with \0 may contain up to four digits), and %q  causes
              printf to output the corresponding argument in a format that can
              be reused as shell input.

              The -v option causes the output to be assigned to  the  variable
              var rather than being printed to the standard output.

              The  format  is  reused  as  necessary  to  consume  all  of the
              arguments.  If the  format  requires  more  arguments  than  are
              supplied,  the  extra  format specifications behave as if a zero
              value or null string, as appropriate, had  been  supplied.   The
              return value is zero on success, non-zero on failure.

       pushd [-n] [+n] [-n]
       pushd [-n] [dir]
              Adds  a  directory to the top of the directory stack, or rotates
              the stack, making the new top of the stack the  current  working
              directory.  With no arguments, exchanges the top two directories
              and returns 0, unless the directory stack is empty.   Arguments,
              if supplied, have the following meanings:
              -n     Suppresses  the  normal  change  of directory when adding
                     directories to the stack,  so  that  only  the  stack  is
                     manipulated.
              +n     Rotates  the  stack  so  that the nth directory (counting
                     from the left of the list shown by  dirs,  starting  with
                     zero) is at the top.
              -n     Rotates  the  stack  so  that the nth directory (counting
                     from the right of the list shown by dirs,  starting  with
                     zero) is at the top.
              dir    Adds dir to the directory stack at the top, making it the
                     new current working directory.

              If the pushd command is successful, a dirs is performed as well.
              If  the first form is used, pushd returns 0 unless the cd to dir
              fails.  With  the  second  form,  pushd  returns  0  unless  the
              directory stack is empty, a non-existent directory stack element
              is specified, or the  directory  change  to  the  specified  new
              current directory fails.

       pwd [-LP]
              Print  the  absolute  pathname of the current working directory.
              The pathname printed contains no symbolic links if the -P option
              is supplied or the -o physical option to the set builtin command
              is enabled.  If the -L option is used, the pathname printed  may
              contain  symbolic links.  The return status is 0 unless an error
              occurs while reading the name of the  current  directory  or  an
              invalid option is supplied.

       read [-ers] [-a aname] [-d delim] [-i text] [-n nchars] [-p prompt] [-t
       timeout] [-u fd] [name ...]
              One  line  is  read  from  the  standard input, or from the file
              descriptor fd supplied as an argument to the -u option, and  the
              first word is assigned to the first name, the second word to the
              second  name,  and  so  on,  with  leftover  words   and   their
              intervening  separators assigned to the last name.  If there are
              fewer words read from the input stream than names, the remaining
              names are assigned empty values.  The characters in IFS are used
              to split the line into words.  The backslash character  (\)  may
              be  used  to  remove  any special meaning for the next character
              read and for line continuation.  Options, if supplied, have  the
              following meanings:
              -a aname
                     The words are assigned to sequential indices of the array
                     variable aname, starting at 0.  aname is unset before any
                     new  values  are  assigned.   Other  name  arguments  are
                     ignored.
              -d delim
                     The first character of delim is  used  to  terminate  the
                     input line, rather than newline.
              -e     If the standard input is coming from a terminal, readline
                     (see  READLINE  above)  is  used  to  obtain  the   line.
                     Readline  uses  the  current (or default, if line editing
                     was not previously active) editing settings.
              -i text
                     If readline is being used  to  read  the  line,  text  is
                     placed into the editing buffer before editing begins.
              -n nchars
                     read  returns after reading nchars characters rather than
                     waiting for a complete line of input.
              -p prompt
                     Display prompt on  standard  error,  without  a  trailing
                     newline, before attempting to read any input.  The prompt
                     is displayed only if input is coming from a terminal.
              -r     Backslash does not  act  as  an  escape  character.   The
                     backslash  is  considered  to  be  part  of the line.  In
                     particular, a backslash-newline pair may not be used as a
                     line continuation.
              -s     Silent  mode.   If  input  is  coming  from  a  terminal,
                     characters are not echoed.
              -t timeout
                     Cause read to time out and return failure if  a  complete
                     line  of  input  is  not  read  within  timeout  seconds.
                     timeout may be a decimal number with a fractional portion
                     following   the  decimal  point.   This  option  is  only
                     effective if read is reading input from a terminal, pipe,
                     or other special file; it has no effect when reading from
                     regular files.  If timeout is 0, read returns success  if
                     input  is  available  on  the  specified file descriptor,
                     failure otherwise.  The exit status is greater  than  128
                     if the timeout is exceeded.
              -u fd  Read input from file descriptor fd.

              If  no  names  are  supplied,  the  line read is assigned to the
              variable REPLY.  The return code is zero, unless end-of-file  is
              encountered,  read  times  out (in which case the return code is
              greater than 128), or an invalid file descriptor is supplied  as
              the argument to -u.

       readonly [-aApf] [name[=word] ...]
              The  given  names are marked readonly; the values of these names
              may not be changed by subsequent assignment.  If the  -f  option
              is  supplied,  the  functions  corresponding to the names are so
              marked.  The  -a  option  restricts  the  variables  to  indexed
              arrays;  the  -A  option  restricts the variables to associative
              arrays.  If no name arguments are given, or if the -p option  is
              supplied,  a  list  of  all  readonly  names is printed.  The -p
              option causes output to be displayed in a  format  that  may  be
              reused  as  input.  If a variable name is followed by =word, the
              value of the variable is set to word.  The return  status  is  0
              unless an invalid option is encountered, one of the names is not
              a valid shell variable name, or -f is supplied with a name  that
              is not a function.

       return [n]
              Causes  a function to exit with the return value specified by n.
              If n is omitted, the return status is that of the  last  command
              executed  in the function body.  If used outside a function, but
              during execution of a script by  the  .   (source)  command,  it
              causes the shell to stop executing that script and return either
              n or the exit status of the last  command  executed  within  the
              script  as  the  exit  status  of the script.  If used outside a
              function and not during execution of a script by .,  the  return
              status is false.  Any command associated with the RETURN trap is
              executed before execution resumes after the function or  script.

       set [--abefhkmnptuvxBCEHPT] [-o option] [arg ...]
       set [+abefhkmnptuvxBCEHPT] [+o option] [arg ...]
              Without  options,  the name and value of each shell variable are
              displayed in a format that can be reused as input for setting or
              resetting  the  currently-set  variables.   Read-only  variables
              cannot be reset.   In  posix  mode,  only  shell  variables  are
              listed.   The  output is sorted according to the current locale.
              When options are specified, they set or unset shell  attributes.
              Any  arguments  remaining after option processing are treated as
              values for the positional parameters and are assigned, in order,
              to  $1,  $2, ...  $n.  Options, if specified, have the following
              meanings:
              -a      Automatically mark variables  and  functions  which  are
                      modified  or  created  for  export to the environment of
                      subsequent commands.
              -b      Report  the  status  of   terminated   background   jobs
                      immediately, rather than before the next primary prompt.
                      This is effective only when job control is enabled.
              -e      Exit immediately if a pipeline (which may consist  of  a
                      single  simple command),  a subshell command enclosed in
                      parentheses, or one of the commands executed as part  of
                      a  command  list  enclosed  by braces (see SHELL GRAMMAR
                      above) exits with a non-zero status.  The shell does not
                      exit  if  the  command that fails is part of the command
                      list immediately following a  while  or  until  keyword,
                      part  of  the  test  following  the  if or elif reserved
                      words, part of any command executed in a && or  ││  list
                      except  the  command  following  the final && or ││, any
                      command in a pipeline but the last, or if the  command’s
                      return  value  is being inverted with !.  A trap on ERR,
                      if set, is executed before the shell exits.  This option
                      applies  to  the  shell  environment  and  each subshell
                      environment   separately    (see    COMMAND    EXECUTION
                      ENVIRONMENT  above),  and  may  cause  subshells to exit
                      before executing all the commands in the subshell.
              -f      Disable pathname expansion.
              -h      Remember the location of commands as they are looked  up
                      for execution.  This is enabled by default.
              -k      All  arguments  in the form of assignment statements are
                      placed in the environment for a command, not just  those
                      that precede the command name.
              -m      Monitor  mode.   Job control is enabled.  This option is
                      on by default for interactive  shells  on  systems  that
                      support   it   (see   JOB  CONTROL  above).   Background
                      processes run in a separate process  group  and  a  line
                      containing  their  exit  status  is  printed  upon their
                      completion.
              -n      Read commands but do not execute them.  This may be used
                      to  check  a  shell  script  for syntax errors.  This is
                      ignored by interactive shells.
              -o option-name
                      The option-name can be one of the following:
                      allexport
                              Same as -a.
                      braceexpand
                              Same as -B.
                      emacs   Use  an   emacs-style   command   line   editing
                              interface.   This is enabled by default when the
                              shell  is  interactive,  unless  the  shell   is
                              started  with the --noediting option.  This also
                              affects the editing interface used for read  -e.
                      errtrace
                              Same as -E.
                      functrace
                              Same as -T.
                      errexit Same as -e.
                      hashall Same as -h.
                      histexpand
                              Same as -H.
                      history Enable command history, as described above under
                              HISTORY.   This  option  is  on  by  default  in
                              interactive shells.
                      ignoreeof
                              The   effect   is   as   if  the  shell  command
                              ‘‘IGNOREEOF=10’’ had been  executed  (see  Shell
                              Variables above).
                      keyword Same as -k.
                      monitor Same as -m.
                      noclobber
                              Same as -C.
                      noexec  Same as -n.
                      noglob  Same as -f.
                      nolog   Currently ignored.
                      notify  Same as -b.
                      nounset Same as -u.
                      onecmd  Same as -t.
                      physical
                              Same as -P.
                      pipefail
                              If  set,  the  return value of a pipeline is the
                              value of the last (rightmost)  command  to  exit
                              with  a non-zero status, or zero if all commands
                              in the pipeline exit successfully.  This  option
                              is disabled by default.
                      posix   Change  the  behavior  of bash where the default
                              operation differs from  the  POSIX  standard  to
                              match the standard (posix mode).
                      privileged
                              Same as -p.
                      verbose Same as -v.
                      vi      Use  a  vi-style command line editing interface.
                              This also affects the editing interface used for
                              read -e.
                      xtrace  Same as -x.
                      If -o is supplied with no option-name, the values of the
                      current options are printed.  If +o is supplied with  no
                      option-name,  a  series  of set commands to recreate the
                      current option settings is  displayed  on  the  standard
                      output.
              -p      Turn  on  privileged  mode.   In this mode, the $ENV and
                      $BASH_ENV files are not processed, shell  functions  are
                      not  inherited  from the environment, and the SHELLOPTS,
                      CDPATH, and GLOBIGNORE variables, if they appear in  the
                      environment,  are ignored.  If the shell is started with
                      the effective user (group) id not equal to the real user
                      (group)  id,  and  the  -p option is not supplied, these
                      actions are taken and the effective user id  is  set  to
                      the  real  user  id.   If  the  -p option is supplied at
                      startup, the effective user id is  not  reset.   Turning
                      this  option off causes the effective user and group ids
                      to be set to the real user and group ids.
              -t      Exit after reading and executing one command.
              -u      Treat unset variables  and  parameters  other  than  the
                      special   parameters  "@"  and  "*"  as  an  error  when
                      performing  parameter  expansion.    If   expansion   is
                      attempted  on  an unset variable or parameter, the shell
                      prints an error message, and, if not interactive,  exits
                      with a non-zero status.
              -v      Print shell input lines as they are read.
              -x      After  expanding  each simple command, for command, case
                      command, select  command,  or  arithmetic  for  command,
                      display  the  expanded  value  of  PS4,  followed by the
                      command and its expanded arguments  or  associated  word
                      list.
              -B      The  shell performs brace expansion (see Brace Expansion
                      above).  This is on by default.
              -C      If set, bash does not overwrite an  existing  file  with
                      the  >,  >&,  and <> redirection operators.  This may be
                      overridden when  creating  output  files  by  using  the
                      redirection operator >| instead of >.
              -E      If set, any trap on ERR is inherited by shell functions,
                      command  substitutions,  and  commands  executed  in   a
                      subshell  environment.   The  ERR  trap  is normally not
                      inherited in such cases.
              -H      Enable !  style history substitution.  This option is on
                      by default when the shell is interactive.
              -P      If  set,  the  shell does not follow symbolic links when
                      executing commands such as cd that  change  the  current
                      working  directory.   It  uses  the  physical  directory
                      structure instead.  By default, bash follows the logical
                      chain  of  directories  when  performing  commands which
                      change the current directory.
              -T      If set, any traps on DEBUG and RETURN are  inherited  by
                      shell  functions,  command  substitutions,  and commands
                      executed in  a  subshell  environment.   The  DEBUG  and
                      RETURN traps are normally not inherited in such cases.
              --      If  no arguments follow this option, then the positional
                      parameters  are  unset.    Otherwise,   the   positional
                      parameters  are  set  to  the args, even if some of them
                      begin with a -.
              -       Signal the end of options, cause all remaining  args  to
                      be assigned to the positional parameters.  The -x and -v
                      options are turned off.   If  there  are  no  args,  the
                      positional parameters remain unchanged.

              The  options are off by default unless otherwise noted.  Using +
              rather than - causes  these  options  to  be  turned  off.   The
              options  can  also be specified as arguments to an invocation of
              the shell.  The current set of options may be found in $-.   The
              return  status  is  always  true  unless  an  invalid  option is
              encountered.

       shift [n]
              The positional parameters from n+1 ... are renamed  to  $1  ....
              Parameters  represented  by  the  numbers  $# down to $#-n+1 are
              unset.  n must be a non-negative number less than  or  equal  to
              $#.   If  n is 0, no parameters are changed.  If n is not given,
              it is assumed to be 1.  If n is greater than $#, the  positional
              parameters  are  not changed.  The return status is greater than
              zero if n is greater than $# or less than zero; otherwise 0.

       shopt [-pqsu] [-o] [optname ...]
              Toggle  the  values  of  variables  controlling  optional  shell
              behavior.  With no options, or with the -p option, a list of all
              settable options is displayed, with an indication of whether  or
              not each is set.  The -p option causes output to be displayed in
              a form that may be reused as  input.   Other  options  have  the
              following meanings:
              -s     Enable (set) each optname.
              -u     Disable (unset) each optname.
              -q     Suppresses  normal output (quiet mode); the return status
                     indicates whether  the  optname  is  set  or  unset.   If
                     multiple  optname arguments are given with -q, the return
                     status is zero if  all  optnames  are  enabled;  non-zero
                     otherwise.
              -o     Restricts  the  values of optname to be those defined for
                     the -o option to the set builtin.

              If either -s or -u  is  used  with  no  optname  arguments,  the
              display  is  limited  to  those  options which are set or unset,
              respectively.  Unless otherwise noted,  the  shopt  options  are
              disabled (unset) by default.

              The  return  status when listing options is zero if all optnames
              are enabled, non-zero  otherwise.   When  setting  or  unsetting
              options,  the  return  status is zero unless an optname is not a
              valid shell option.

              The list of shopt options is:

              autocd  If set, a command name that is the name of  a  directory
                      is  executed  as  if  it  were  the  argument  to the cd
                      command.   This  option  is  only  used  by  interactive
                      shells.
              cdable_vars
                      If  set,  an  argument to the cd builtin command that is
                      not a directory is assumed to be the name of a  variable
                      whose value is the directory to change to.
              cdspell If  set,  minor  errors  in  the spelling of a directory
                      component in a cd command will be corrected.  The errors
                      checked   for   are  transposed  characters,  a  missing
                      character, and one character too many.  If a  correction
                      is  found,  the  corrected file name is printed, and the
                      command  proceeds.   This  option  is   only   used   by
                      interactive shells.
              checkhash
                      If  set,  bash  checks  that a command found in the hash
                      table exists before trying to execute it.  If  a  hashed
                      command  no  longer  exists,  a  normal  path  search is
                      performed.
              checkjobs
                      If set, bash lists the status of any stopped and running
                      jobs  before  exiting an interactive shell.  If any jobs
                      are running, this causes the exit to be deferred until a
                      second  exit is attempted without an intervening command
                      (see JOB CONTROL above).   The  shell  always  postpones
                      exiting if any jobs are stopped.
              checkwinsize
                      If  set,  bash checks the window size after each command
                      and, if necessary,  updates  the  values  of  LINES  and
                      COLUMNS.
              cmdhist If  set,  bash attempts to save all lines of a multiple-
                      line command in the same  history  entry.   This  allows
                      easy re-editing of multi-line commands.
              compat31
                      If set, bash changes its behavior to that of version 3.1
                      with respect to  quoted  arguments  to  the  conditional
                      command’s =~ operator.
              dirspell
                      If  set,  bash attempts spelling correction on directory
                      names during  word  completion  if  the  directory  name
                      initially supplied does not exist.
              dotglob If  set, bash includes filenames beginning with a ‘.’ in
                      the results of pathname expansion.
              execfail
                      If set, a non-interactive shell  will  not  exit  if  it
                      cannot  execute the file specified as an argument to the
                      exec builtin command.  An  interactive  shell  does  not
                      exit if exec fails.
              expand_aliases
                      If  set,  aliases  are expanded as described above under
                      ALIASES.   This  option  is  enabled  by   default   for
                      interactive shells.
              extdebug
                      If  set,  behavior  intended  for  use  by  debuggers is
                      enabled:
                      1.     The -F option to the declare builtin displays the
                             source file name and line number corresponding to
                             each function name supplied as an argument.
                      2.     If the command run by the DEBUG  trap  returns  a
                             non-zero  value,  the next command is skipped and
                             not executed.
                      3.     If the command run by the DEBUG  trap  returns  a
                             value  of  2,  and  the  shell  is executing in a
                             subroutine (a shell function or  a  shell  script
                             executed  by the . or source builtins), a call to
                             return is simulated.
                      4.     BASH_ARGC and BASH_ARGV are updated as  described
                             in their descriptions above.
                      5.     Function    tracing    is    enabled:     command
                             substitution,  shell  functions,  and   subshells
                             invoked  with  (  command ) inherit the DEBUG and
                             RETURN traps.
                      6.     Error tracing is enabled:  command  substitution,
                             shell  functions,  and  subshells  invoked with (
                             command ) inherit the ERROR trap.
              extglob If set, the extended pattern matching features described
                      above under Pathname Expansion are enabled.
              extquote
                      If  set,  $'string'  and  $"string" quoting is performed
                      within  ${parameter}  expansions  enclosed   in   double
                      quotes.  This option is enabled by default.
              failglob
                      If  set,  patterns  which fail to match filenames during
                      pathname expansion result in an expansion error.
              force_fignore
                      If set, the suffixes  specified  by  the  FIGNORE  shell
                      variable  cause words to be ignored when performing word
                      completion even  if  the  ignored  words  are  the  only
                      possible  completions.   See SHELL VARIABLES above for a
                      description of  FIGNORE.   This  option  is  enabled  by
                      default.
              globstar
                      If  set,  the  pattern  **  used in a filename expansion
                      context will match a files and zero or more  directories
                      and  subdirectories.  If the pattern is followed by a /,
                      only directories and subdirectories match.
              gnu_errfmt
                      If set, shell error messages are written in the standard
                      GNU error message format.
              histappend
                      If  set,  the history list is appended to the file named
                      by the value of the HISTFILE  variable  when  the  shell
                      exits, rather than overwriting the file.
              histreedit
                      If  set, and readline is being used, a user is given the
                      opportunity to re-edit a failed history substitution.
              histverify
                      If set, and readline  is  being  used,  the  results  of
                      history  substitution  are not immediately passed to the
                      shell parser.  Instead, the  resulting  line  is  loaded
                      into  the  readline  editing  buffer,  allowing  further
                      modification.
              hostcomplete
                      If set, and readline is being used, bash will attempt to
                      perform  hostname  completion when a word containing a @
                      is  being  completed  (see  Completing  under   READLINE
                      above).  This is enabled by default.
              huponexit
                      If  set,  bash  will  send  SIGHUP  to  all jobs when an
                      interactive login shell exits.
              interactive_comments
                      If set, allow a word beginning with # to cause that word
                      and  all remaining characters on that line to be ignored
                      in an interactive  shell  (see  COMMENTS  above).   This
                      option is enabled by default.
              lithist If  set,  and  the cmdhist option is enabled, multi-line
                      commands are saved to the history with embedded newlines
                      rather than using semicolon separators where possible.
              login_shell
                      The  shell  sets this option if it is started as a login
                      shell (see INVOCATION above).   The  value  may  not  be
                      changed.
              mailwarn
                      If  set,  and  a file that bash is checking for mail has
                      been accessed since the last time it  was  checked,  the
                      message  ‘‘The  mail  in  mailfile  has  been  read’’ is
                      displayed.
              no_empty_cmd_completion
                      If set, and  readline  is  being  used,  bash  will  not
                      attempt to search the PATH for possible completions when
                      completion is attempted on an empty line.
              nocaseglob
                      If set, bash matches  filenames  in  a  case-insensitive
                      fashion when performing pathname expansion (see Pathname
                      Expansion above).
              nocasematch
                      If set, bash  matches  patterns  in  a  case-insensitive
                      fashion when performing matching while executing case or
                      [[ conditional commands.
              nullglob
                      If set, bash allows patterns which match no  files  (see
                      Pathname  Expansion  above)  to expand to a null string,
                      rather than themselves.
              progcomp
                      If set,  the  programmable  completion  facilities  (see
                      Programmable Completion above) are enabled.  This option
                      is enabled by default.
              promptvars
                      If set,  prompt  strings  undergo  parameter  expansion,
                      command  substitution,  arithmetic  expansion, and quote
                      removal after being expanded as described  in  PROMPTING
                      above.  This option is enabled by default.
              restricted_shell
                      The   shell  sets  this  option  if  it  is  started  in
                      restricted mode (see RESTRICTED SHELL below).  The value
                      may  not be changed.  This is not reset when the startup
                      files  are  executed,  allowing  the  startup  files  to
                      discover whether or not a shell is restricted.
              shift_verbose
                      If  set,  the shift builtin prints an error message when
                      the  shift  count  exceeds  the  number  of   positional
                      parameters.
              sourcepath
                      If set, the source (.) builtin uses the value of PATH to
                      find the directory containing the file  supplied  as  an
                      argument.  This option is enabled by default.
              xpg_echo
                      If   set,  the  echo  builtin  expands  backslash-escape
                      sequences by default.
       suspend [-f]
              Suspend the execution of this shell until it receives a  SIGCONT
              signal.  A login shell cannot be suspended; the -f option can be
              used to override this and  force  the  suspension.   The  return
              status  is  0  unless  the  shell is a login shell and -f is not
              supplied, or if job control is not enabled.
       test expr
       [ expr ]
              Return a status of 0 or 1 depending on  the  evaluation  of  the
              conditional  expression expr.  Each operator and operand must be
              a separate argument.  Expressions are composed of the  primaries
              described  above  under  CONDITIONAL EXPRESSIONS.  test does not
              accept any options, nor does it accept and ignore an argument of
              -- as signifying the end of options.

              Expressions  may  be  combined  using  the  following operators,
              listed  in  decreasing  order  of  precedence.   The  evaluation
              depends on the number of arguments; see below.
              ! expr True if expr is false.
              ( expr )
                     Returns  the value of expr.  This may be used to override
                     the normal precedence of operators.
              expr1 -a expr2
                     True if both expr1 and expr2 are true.
              expr1 -o expr2
                     True if either expr1 or expr2 is true.

              test and [ evaluate conditional expressions using a set of rules
              based on the number of arguments.

              0 arguments
                     The expression is false.
              1 argument
                     The expression is true if and only if the argument is not
                     null.
              2 arguments
                     If the first argument is !, the expression is true if and
                     only  if  the  second  argument  is  null.   If the first
                     argument is one of the unary conditional operators listed
                     above  under  CONDITIONAL  EXPRESSIONS, the expression is
                     true if the unary test is true.  If the first argument is
                     not a valid unary conditional operator, the expression is
                     false.
              3 arguments
                     If the second argument is one of the  binary  conditional
                     operators listed above under CONDITIONAL EXPRESSIONS, the
                     result of the expression is the result of the binary test
                     using  the first and third arguments as operands.  The -a
                     and -o operators are  considered  binary  operators  when
                     there  are  three arguments.  If the first argument is !,
                     the value is the negation of the two-argument test  using
                     the second and third arguments.  If the first argument is
                     exactly ( and the third argument is exactly ), the result
                     is   the   one-argument  test  of  the  second  argument.
                     Otherwise, the expression is false.
              4 arguments
                     If the first argument is !, the result is the negation of
                     the  three-argument  expression composed of the remaining
                     arguments.   Otherwise,  the  expression  is  parsed  and
                     evaluated  according to precedence using the rules listed
                     above.
              5 or more arguments
                     The expression  is  parsed  and  evaluated  according  to
                     precedence using the rules listed above.

       times  Print  the  accumulated  user and system times for the shell and
              for processes run from the shell.  The return status is 0.

       trap [-lp] [[arg] sigspec ...]
              The command arg is to  be  read  and  executed  when  the  shell
              receives  signal(s)  sigspec.   If arg is absent (and there is a
              single sigspec) or -, each specified  signal  is  reset  to  its
              original  disposition  (the  value  it  had upon entrance to the
              shell).  If arg is the null string the signal specified by  each
              sigspec  is ignored by the shell and by the commands it invokes.
              If arg is not present and -p has been supplied,  then  the  trap
              commands  associated  with  each  sigspec  are displayed.  If no
              arguments are supplied or if only -p is given, trap  prints  the
              list  of  commands  associated  with each signal.  The -l option
              causes the shell to print a  list  of  signal  names  and  their
              corresponding  numbers.   Each  sigspec  is either a signal name
              defined in <signal.h>, or a signal  number.   Signal  names  are
              case  insensitive  and the SIG prefix is optional.  If a sigspec
              is EXIT (0) the command arg is executed on exit from the  shell.
              If  a sigspec is DEBUG, the command arg is executed before every
              simple command, for command, case command, select command, every
              arithmetic for command, and before the first command executes in
              a shell function  (see  SHELL  GRAMMAR  above).   Refer  to  the
              description  of  the  extdebug  option  to the shopt builtin for
              details of its effect on the DEBUG trap.  If a sigspec  is  ERR,
              the  command  arg  is  executed  whenever a simple command has a
              non-zero exit status, subject to the following conditions.   The
              ERR  trap  is  not executed if the failed command is part of the
              command list immediately following a  while  or  until  keyword,
              part  of the test in an if statement, part of a command executed
              in a && or ││ list, or if the command’s return  value  is  being
              inverted  via  !.   These  are the same conditions obeyed by the
              errexit option.  If a sigspec is  RETURN,  the  command  arg  is
              executed  each  time  a shell function or a script executed with
              the . or source builtins finishes  executing.   Signals  ignored
              upon  entry  to  the  shell cannot be trapped or reset.  Trapped
              signals that are not being ignored are reset to  their  original
              values in a child process when it is created.  The return status
              is false if any sigspec is invalid; otherwise trap returns true.

       type [-aftpP] name [name ...]
              With  no options, indicate how each name would be interpreted if
              used as a command name.  If the -t option is used, type prints a
              string  which  is  one  of alias, keyword, function, builtin, or
              file if  name  is  an  alias,  shell  reserved  word,  function,
              builtin,  or disk file, respectively.  If the name is not found,
              then nothing  is  printed,  and  an  exit  status  of  false  is
              returned.   If  the  -p  option is used, type either returns the
              name of the disk file  that  would  be  executed  if  name  were
              specified  as  a  command  name,  or nothing if ‘‘type -t name’’
              would not return file.  The -P option forces a PATH  search  for
              each name, even if ‘‘type -t name’’ would not return file.  If a
              command is hashed,  -p  and  -P  print  the  hashed  value,  not
              necessarily  the  file  that  appears  first in PATH.  If the -a
              option is used, type prints all of the places  that  contain  an
              executable  named name.  This includes aliases and functions, if
              and only if the -p option is not also used.  The table of hashed
              commands  is  not  consulted  when  using  -a.   The  -f  option
              suppresses shell function lookup, as with the  command  builtin.
              type  returns  true  if all of the arguments are found, false if
              any are not found.

       ulimit [-HSTabcdefilmnpqrstuvx [limit]]
              Provides control over the resources available to the  shell  and
              to  processes started by it, on systems that allow such control.
              The -H and -S options specify that the hard or soft limit is set
              for  the  given resource.  A hard limit cannot be increased by a
              non-root user once it is set; a soft limit may be  increased  up
              to  the  value  of  the  hard  limit.   If  neither -H nor -S is
              specified, both the soft and hard limits are set.  The value  of
              limit  can be a number in the unit specified for the resource or
              one of the special values hard, soft, or unlimited, which  stand
              for  the  current  hard  limit,  the  current soft limit, and no
              limit, respectively.  If limit is omitted, the current value  of
              the  soft limit of the resource is printed, unless the -H option
              is given.  When more than one resource is specified,  the  limit
              name  and  unit are printed before the value.  Other options are
              interpreted as follows:
              -a     All current limits are reported
              -b     The maximum socket buffer size
              -c     The maximum size of core files created
              -d     The maximum size of a process’s data segment
              -e     The maximum scheduling priority ("nice")
              -f     The maximum size of files written by the  shell  and  its
                     children
              -i     The maximum number of pending signals
              -l     The maximum size that may be locked into memory
              -m     The  maximum resident set size (many systems do not honor
                     this limit)
              -n     The maximum number of open file descriptors (most systems
                     do not allow this value to be set)
              -p     The pipe size in 512-byte blocks (this may not be set)
              -q     The maximum number of bytes in POSIX message queues
              -r     The maximum real-time scheduling priority
              -s     The maximum stack size
              -t     The maximum amount of cpu time in seconds
              -u     The  maximum  number  of  processes available to a single
                     user
              -v     The maximum amount of virtual  memory  available  to  the
                     shell
              -x     The maximum number of file locks
              -T     The maximum number of threads

              If limit is given, it is the new value of the specified resource
              (the -a option is display only).  If no option is given, then -f
              is  assumed.  Values are in 1024-byte increments, except for -t,
              which is in seconds, -p, which is in units of  512-byte  blocks,
              and  -T,  -b, -n, and -u, which are unscaled values.  The return
              status is 0 unless an invalid option or argument is supplied, or
              an error occurs while setting a new limit.

       umask [-p] [-S] [mode]
              The user file-creation mask is set to mode.  If mode begins with
              a digit, it is interpreted as an octal number; otherwise  it  is
              interpreted  as a symbolic mode mask similar to that accepted by
              chmod(1).  If mode is omitted, the current value of the mask  is
              printed.   The  -S  option  causes  the  mask  to  be printed in
              symbolic form; the default output is an octal number.  If the -p
              option is supplied, and mode is omitted, the output is in a form
              that may be reused as input.  The return status is 0 if the mode
              was  successfully  changed  or if no mode argument was supplied,
              and false otherwise.

       unalias [-a] [name ...]
              Remove each name from the list of defined  aliases.   If  -a  is
              supplied,  all  alias definitions are removed.  The return value
              is true unless a supplied name is not a defined alias.

       unset [-fv] [name ...]
              For each name, remove the corresponding  variable  or  function.
              If no options are supplied, or the -v option is given, each name
              refers to a shell variable.   Read-only  variables  may  not  be
              unset.   If  -f  is  specified,  each  name  refers  to  a shell
              function, and the function definition is  removed.   Each  unset
              variable  or  function is removed from the environment passed to
              subsequent  commands.   If  any  of  RANDOM,  SECONDS,   LINENO,
              HISTCMD,  FUNCNAME,  GROUPS,  or  DIRSTACK  are unset, they lose
              their special properties, even if they are  subsequently  reset.
              The exit status is true unless a name is readonly.

       wait [n ...]
              Wait  for  each  specified  process  and  return its termination
              status.  Each n may be a process ID or a job specification; if a
              job  spec  is  given,  all  processes in that job’s pipeline are
              waited for.  If n is  not  given,  all  currently  active  child
              processes  are  waited for, and the return status is zero.  If n
              specifies a non-existent process or job, the  return  status  is
              127.   Otherwise,  the  return  status is the exit status of the
              last process or job waited for.

RESTRICTED SHELL

       If bash is started with the name rbash, or the -r option is supplied at
       invocation,  the  shell becomes restricted.  A restricted shell is used
       to set up an environment more controlled than the standard  shell.   It
       behaves  identically  to bash with the exception that the following are
       disallowed or not performed:

       ·      changing directories with cd

       ·      setting or unsetting the values of SHELL, PATH, ENV, or BASH_ENV

       ·      specifying command names containing /

       ·      specifying  a  file  name containing a / as an argument to the .
              builtin command

       ·      Specifying a filename containing a slash as an argument  to  the
              -p option to the hash builtin command

       ·      importing  function  definitions  from  the shell environment at
              startup

       ·      parsing the value of SHELLOPTS from  the  shell  environment  at
              startup

       ·      redirecting  output  using  the  >,  >|,  <>,  >&,  &>,  and  >>
              redirection operators

       ·      using the exec builtin command to replace the shell with another
              command

       ·      adding  or  deleting builtin commands with the -f and -d options
              to the enable builtin command

       ·      Using the  enable  builtin  command  to  enable  disabled  shell
              builtins

       ·      specifying the -p option to the command builtin command

       ·      turning off restricted mode with set +r or set +o restricted.

       These restrictions are enforced after any startup files are read.

       When  a  command  that  is  found to be a shell script is executed (see
       COMMAND EXECUTION above), rbash turns off any restrictions in the shell
       spawned to execute the script.

SEE ALSO

       Bash Reference Manual, Brian Fox and Chet Ramey
       The Gnu Readline Library, Brian Fox and Chet Ramey
       The Gnu History Library, Brian Fox and Chet Ramey
       Portable   Operating   System  Interface  (POSIX)  Part  2:  Shell  and
       Utilities, IEEE
       sh(1), ksh(1), csh(1)
       emacs(1), vi(1)
       readline(3)

FILES

       /bin/bash
              The bash executable
       /etc/profile
              The systemwide initialization file, executed for login shells
       /etc/bash.bashrc
              The systemwide per-interactive-shell startup file
       /etc/bash.bash.logout
              The  systemwide  login shell cleanup file, executed when a login
              shell exits
       ~/.bash_profile
              The personal initialization file, executed for login shells
       ~/.bashrc
              The individual per-interactive-shell startup file
       ~/.bash_logout
              The individual login shell cleanup file, executed when  a  login
              shell exits
       ~/.inputrc
              Individual readline initialization file

AUTHORS

       Brian Fox, Free Software Foundation
       bfox@gnu.org

       Chet Ramey, Case Western Reserve University
       chet.ramey@case.edu

BUG REPORTS

       If you find a bug in bash, you should report it.  But first, you should
       make sure that it really is a bug, and that it appears  in  the  latest
       version   of  bash.   The  latest  version  is  always  available  from
       ftp://ftp.gnu.org/pub/bash/.

       Once you have determined that a bug actually exists,  use  the  bashbug
       command  to submit a bug report.  If you have a fix, you are encouraged
       to mail that as well!  Suggestions and ‘philosophical’ bug reports  may
       be  mailed  to  bug-bash@gnu.org  or  posted  to  the  Usenet newsgroup
       gnu.bash.bug.

       ALL bug reports should include:

       The version number of bash
       The hardware and operating system
       The compiler used to compile
       A description of the bug behaviour
       A short script or ‘recipe’ which exercises the bug

       bashbug inserts the first three items automatically into  the  template
       it provides for filing a bug report.

       Comments and bug reports concerning this manual page should be directed
       to chet@po.cwru.edu.

BUGS

       It’s too big and too slow.

       There are some subtle differences between bash and traditional versions
       of sh, mostly because of the POSIX specification.

       Aliases are confusing in some uses.

       Shell builtin commands and functions are not stoppable/restartable.

       Compound commands and command sequences of the form ‘a ; b ; c’ are not
       handled gracefully  when  process  suspension  is  attempted.   When  a
       process  is stopped, the shell immediately executes the next command in
       the sequence.  It suffices to place the sequence  of  commands  between
       parentheses  to  force  it  into  a subshell, which may be stopped as a
       unit.

       Array variables may not (yet) be exported.

       There may be only one active coprocess at a time.