Provided by: ksh93u+m_1.0.4-3_amd64 bug

NAME

       ksh, rksh - KornShell, a standard/restricted command and programming language

SYNOPSIS

       ksh [ ±abcefhiklmnprstuvxBCDEGH ] [ ±o option ] ... [ - ] [ arg ... ]
       rksh [ ±abcefhiklmnpstuvxBCDEGH ] [ ±o option ] ... [ - ] [ arg ... ]

DESCRIPTION

       Ksh is a command and programming language that executes commands read from a terminal or a
       file.  Rksh is a restricted version of the command interpreter ksh; it is used to  set  up
       login  names  and execution environments whose capabilities are more controlled than those
       of the standard shell.  See Invocation below for the meaning of arguments to the shell.

   Definitions.
       A metacharacter is one of the following characters:

              ;   &   (   )   |   <   >   new-line   space   tab

       A blank is a tab or a  space.   An  identifier  is  a  sequence  of  letters,  digits,  or
       underscores  starting  with a letter or underscore.  Identifiers are used as components of
       variable names.  A vname is a sequence of one or more identifiers separated  by  a  .  and
       optionally  preceded by a ..  Vnames are used as function and variable names.  A word is a
       sequence of characters from the character set defined by  the  current  locale,  excluding
       non-quoted metacharacters.

       A  command  is  a  sequence  of characters in the syntax of the shell language.  The shell
       reads each command and carries out the desired  action  either  directly  or  by  invoking
       separate  utilities.   A  built-in  command  is a command that is carried out by the shell
       itself without creating a separate  process.   Some  commands  are  built  in  purely  for
       convenience  and  are not documented here.  Built-ins that cause side effects in the shell
       environment and built-ins that are found before performing a path  search  (see  Execution
       below)  are  documented  here.   For  historical  reasons,  some of these built-ins behave
       differently than other built-ins and are called special built-ins.

   Commands.
       A simple-command is a list of variable assignments (see Variable Assignments below)  or  a
       sequence  of blank separated words which may be preceded by a list of variable assignments
       (see Environment below).  The first word specifies the name of the command to be executed.
       Except  as  specified  below,  the  remaining words are passed as arguments to the invoked
       command.  The command name is passed as argument 0 (see exec(2)).  The value of a  simple-
       command  is  its exit status; 0-255 if it terminates normally; 256+signum if it terminates
       abnormally (the name of the signal corresponding to the exit status can  be  obtained  via
       the -l option of the kill built-in utility).

       A  pipeline  is a sequence of one or more commands separated by |.  The standard output of
       each command but the last is connected by a socketpair(2) or (if the posix shell option is
       on)  by a pipe(2) to the standard input of the next command.  Each command except the last
       is run asynchronously in a subshell (see Subshells below).  If  the  monitor  or  pipefail
       option  is on, or the pipeline is preceded by the reserved word time, then the shell waits
       for all component commands in the pipeline to terminate; otherwise, the shell  only  waits
       for  the  last component command.  The exit status of a pipeline is the exit status of its
       last component command, unless the pipefail option  is  enabled.   Each  pipeline  can  be
       preceded  by the reserved word !  which causes the exit status of the pipeline to become 0
       if the exit status of the last command is non-zero, and 1 if the exit status of  the  last
       command is 0.

       A  list  is  a  sequence  of  one  or more pipelines separated by ;, &, |&, &&, or ||, and
       optionally terminated by ;, &, or |&.  Of these five symbols, ;,  &,  and  |&  have  equal
       precedence,  which is lower than that of && and ||.  The symbols && and || also have equal
       precedence.  A semicolon (;) causes sequential execution of  the  preceding  pipeline;  an
       ampersand  (&)  causes  asynchronous  execution of the preceding pipeline (i.e., the shell
       does not wait for that pipeline to finish).  The symbol |& causes  asynchronous  execution
       of  the  preceding  pipeline  with  a  two-way  pipe  established to the parent shell; the
       standard input and output of the spawned pipeline can be written to and read from  by  the
       parent shell by applying the redirection operators <& and >& with arg p to commands and by
       using -p option of the built-in commands read and print described later.   The  symbol  &&
       (||)  causes the list following it to be executed only if the preceding pipeline returns a
       zero (non-zero) value.  One or more new-lines may appear in a list instead of a semicolon,
       to  delimit  a  command.  The first item  of the first pipeline of a list that is a simple
       command not beginning with a redirection, and not occurring within a while, until,  or  if
       list,  can be preceded by a semicolon.  This semicolon is ignored unless the showme option
       is enabled as described with the set built-in below.

       A command is either a simple-command or one of the following.   Unless  otherwise  stated,
       the  value  returned  by  a  command  is  that  of the last simple-command executed in the
       command.

       for vname [ in word ... ] ;do list ;done
              Each time a for command is executed, vname is set to the next word taken  from  the
              in  word  list.   If  in word ...  is omitted, then the for command executes the do
              list once for each positional parameter that is set starting from 1 (see  Parameter
              Expansion below).  Execution ends when there are no more words in the list.

       for (( [expr1] ; [expr2] ; [expr3] )) ;do list ;done
              The  arithmetic  expression  expr1  is  evaluated  first (see Arithmetic Evaluation
              below).  The arithmetic expression expr2 is repeatedly evaluated until it evaluates
              to  zero  and  when  non-zero, list is executed and the arithmetic expression expr3
              evaluated.  If any expression is omitted, then it behaves as if it evaluated to 1.

       select vname [ in word ... ] ;do list ;done
              A select command prints on standard error (file descriptor 2)  the  set  of  words,
              each  preceded  by  a  number.   If  in  word  ...  is omitted, then the positional
              parameters starting from 1 are used instead (see Parameter Expansion  below).   The
              PS3  prompt  is  printed  and a line is read from the standard input.  If this line
              consists of the number of one of the listed words, then the value of  the  variable
              vname  is set to the word corresponding to this number.  If this line is empty, the
              selection list is printed again.  Otherwise the value of the variable vname is  set
              to the empty string.  The contents of the line read from standard input is saved in
              the variable REPLY.  The list is executed for each selection until a break or  end-
              of-file  is  encountered.   If the REPLY variable is set to the empty string by the
              execution of list, then the selection list is printed  before  displaying  the  PS3
              prompt for the next selection.

       case word in [ [(]pattern [ | pattern ] ... ) list ;; ] ... esac
              A  case  command  executes  the list associated with the first pattern that matches
              word.  The form of the patterns is the same as that  used  for  pathname  expansion
              (see  Pathname  Expansion  below).   The  ;;  operator  causes execution of case to
              terminate.  If ;& is used in place of ;; the next  subsequent  list,  if  any,   is
              executed.

       if list ;then list [ ;elif list ;then list ] ... [ ;else list ] ;fi
              The  list  following if is executed and, if it returns a zero exit status, the list
              following the first then is  executed.   Otherwise,  the  list  following  elif  is
              executed  and,  if its value is zero, the list following the next then is executed.
              Failing each successive elif list, the else list is executed.  If the if  list  has
              non-zero  exit status and there is no else list, then the if command returns a zero
              exit status.

       while list ;do list ;done
       until list ;do list ;done
              A while command repeatedly executes the while list and, if the exit status  of  the
              last  command  in  the  list  is  zero,  executes  the  do list; otherwise the loop
              terminates.  If no commands in the do list are executed,  then  the  while  command
              returns  a zero exit status; until may be used in place of while to negate the loop
              termination test.

       while inputredirection ;do list ;done
              Filescan loop. This is defined by a lone input  redirection  following  while  (see
              Input/Output  below).   It  is  faster  than  using  the read built-in command in a
              regular while loop.  The shell reads lines  from  the  file  or  stream  opened  by
              inputredirection  until  the  end  is reached or the loop is broken.  For each line
              read, the command list is executed with the line's contents assigned to  the  REPLY
              variable  and  the  line's  fields  split into the positional parameters (see Field
              Splitting and Positional Parameters below).  Within the  list,  standard  input  is
              redirected  to /dev/null.  If the posix compatibility shell option is on, this loop
              type is disabled and inputredirection is processed like a lone redirection  in  any
              other context.

       ((expression))
              The  expression  is  evaluated  using the rules for arithmetic evaluation described
              below.  If the value of the arithmetic expression is non-zero, the exit  status  is
              0, otherwise the exit status is 1.

       (list)
              Execute  list in a subshell (see Subshells below).  Note, that if two adjacent open
              parentheses are needed for nesting, a space must be inserted to avoid evaluation as
              an arithmetic command as described above.

       { list;}
              list  is simply executed.  Note that unlike the metacharacters ( and ), { and } are
              reserved words and must occur at the beginning of a line or after a ; in  order  to
              be recognized.

       [[ expression ]]
              Evaluates  expression  and returns a zero exit status when expression is true.  See
              Conditional Expressions below, for a description of expression.

       function varname { list ;}
       varname () { list ;}
              Define a function which  is  referenced  by  varname.   A  function  whose  varname
              contains  a  .   is  called  a  discipline  function and the portion of the varname
              preceding the last .  must refer to an existing variable.  The body of the function
              is  the  list  of  commands  between { and }.  A function defined with the function
              varname syntax can also be used as an argument to the .  special  built-in  command
              to  get  the equivalent behavior as if the varname() syntax were used to define it.
              (See Functions below.)

       namespace identifier { list ;}
              Defines or uses the name space identifier and runs the commands  in  list  in  this
              name space.  (See Name Spaces below.)

       & [ name [ arg... ]  ]
              Causes  subsequent list commands terminated by & to be placed in the background job
              pool name.  If name is omitted a default unnamed pool is used.  Commands in a named
              background pool may be executed remotely.

       time [ pipeline ]
              If pipeline is omitted the user and system time for the current shell and completed
              child processes is printed on standard error.  Otherwise, pipeline is executed  and
              the elapsed time as well as the user and system time are printed on standard error.
              The TIMEFORMAT variable may be set to a format string that specifies how the timing
              information  should  be  displayed.  See Shell Variables below for a description of
              the TIMEFORMAT variable.

       The following reserved words are recognized as reserved only when they are the first  word
       of a command and are not quoted:

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

   Variable Assignments.
       One  or  more  variable  assignments can start a simple command or can be arguments to the
       typeset, enum, export,  or  readonly  special  built-in  commands  as  well  as  to  other
       declaration commands created as types.  The syntax for an assignment is of the form:

       varname=word
       varname[word]=word
              No space is permitted between varname and the = or between = and word.

       varname=(assign_list)
              No  space  is  permitted  between varname and the =.  The variable varname is unset
              before the assignment.  An assign_list can be one of the following:
                      word ...
                             Indexed array assignment.
                      [word]=word ...
                             Associative array assignment.  If preceded by typeset -a  this  will
                             create an indexed array instead.
                      assignment ...
                             Compound  variable  assignment.   This  creates  a compound variable
                             varname with subvariables of the form varname.name,  where  name  is
                             the  name  portion of assignment.  The value of varname will contain
                             all  the  assignment  elements.   Additional  assignments  made   to
                             subvariables  of varname will also be displayed as part of the value
                             of varname.  If no assignments are  specified,  varname  will  be  a
                             compound variable allowing subsequence child elements to be defined.
                      typeset [options] assignment ...
                             Nested  variable  assignment.  Multiple assignments can be specified
                             by separating each of them with a ;.  The previous  value  is  unset
                             before the assignment.  Other declaration commands such as readonly,
                             enum, and other  declaration  commands  can  be  used  in  place  of
                             typeset.
                      . filename
                             Include the assignment commands contained in filename.

       In  addition,  a += can be used in place of the = to signify adding to or appending to the
       previous value.  When += is applied to  an  arithmetic  type,  word  is  evaluated  as  an
       arithmetic  expression and added to the current value.  When applied to a string variable,
       the value defined by word is  appended  to  the  value.   For  compound  assignments,  the
       previous  value  is not unset and the new values are appended to the current ones provided
       that the types are compatible.

       The right hand side of a variable assignment undergoes  all  the  expansion  listed  below
       except  word  splitting, brace expansion, and pathname expansion.  When the left hand side
       is an assignment is a compound variable and the right hand  is  the  name  of  a  compound
       variable,  the  compound  variable on the right will be copied or appended to the compound
       variable on the left.

   Comments.
       A word beginning with # causes that word and all the following characters up to a new-line
       to be ignored.

   Aliasing.
       The  first  word  of each command is replaced by the text of an alias if an alias for this
       word has been defined.  An alias name consists  of  any  number  of  characters  excluding
       metacharacters,  quoting  characters,  file  expansion characters, parameter expansion and
       command substitution characters, the characters /  and  =.   The  replacement  string  can
       contain  any valid shell script including the metacharacters listed above.  The first word
       of each command in the replaced text, other than any that are  in  the  process  of  being
       replaced, will be tested for aliases.  If the last character of the alias value is a blank
       then the word following the alias will also be checked for  alias  substitution.   Aliases
       can  be  used  to  redefine  built-in commands but cannot be used to redefine the reserved
       words listed above.  Aliases can be created and listed with the alias command and  can  be
       removed with the unalias command.

       Aliasing  is performed when scripts are read, not while they are executed.  Therefore, for
       an alias to take effect, the alias definition  command  has  to  be  executed  before  the
       command which references the alias is read.

       The following aliases are automatically preset when the shell is invoked as an interactive
       shell.  Preset aliases can be unset or redefined.
                           history=′hist -l′
                           r=′hist -s′

   Tilde Expansion.
       After alias substitution is performed, each word is checked to see if it  begins  with  an
       unquoted  .   For  tilde  expansion,  word  also  refers to the word portion of parameter
       expansion (see Parameter Expansion below).  If a word is preceded by a tilde, then  it  is
       checked  up  to  a  /  to  see  if  it  matches  a user name in the password database (see
       getpwname(3)).  If a match is found, the  and the matched login name are replaced by  the
       login  directory  of  the  matched  user.  If no match is found, the original text is left
       unchanged.  A  by itself, or in front of a /, is  replaced  by  $HOME,  unless  the  HOME
       variable  is  unset,  in which case the current user's home directory as configured in the
       operating system is used.  A  followed by a +  or  -  is  replaced  by  $PWD  or  $OLDPWD
       respectively.

       In  addition, when expanding a variable assignment (see Variable Assignments above), tilde
       expansion is attempted when the value of the assignment begins with a  ,  and  when  a  
       appears after a :.  A : also terminates a user name following a .

       The  tilde  expansion  mechanism  may  be  extended  or  modified  by  defining one of the
       discipline  functions  .sh.tilde.set  or  .sh.tilde.get  (see  Functions  and   Discipline
       Functions  below).   If either exists, then upon encountering a tilde word to expand, that
       function is called with the tilde word assigned to either .sh.value (for the .sh.tilde.set
       function)  or  .sh.tilde  (for  the  .sh.tilde.get  function).  Performing tilde expansion
       within a discipline function will not recursively call that function,  but  default  tilde
       expansion remains active, so literal tildes should still be quoted where required.  Either
       function may assign a replacement string to .sh.value.  If this  value  is  non-empty  and
       does  not  start  with  a  ,  it  replaces  the default tilde expansion when the function
       terminates.  Otherwise, the tilde expansion is left unchanged.

   Subshells.
       A subshell is a separate execution environment that is a complete duplicate of the current
       shell  environment, except for two things: all traps are reset to default except those for
       signals that are being ignored, and subshells cannot be interactive (i.e.,  they  have  no
       command  prompt).  Changes made within a subshell do not affect the parent environment and
       are lost when the subshell exits.

       Particular care should be taken not to confuse a subshell with a newly invoked shell  that
       is  merely a child process of the current shell, and which (unlike a subshell) starts from
       scratch in terms of variables and functions and  may  be  interactive.   Beware  of  shell
       tutorials on the Internet that confuse these.

       Subshells   are   not   themselves  invoked  as  commands.   Instead,  the  following  are
       automatically run in or from a subshell:

               •  any command or group of commands enclosed in parentheses;

               •  command substitutions of the first and third  form  (see  Command  Substitution
                  below);

               •  process substitutions (see Process Substitution below);

               •  all elements of a pipeline except the last;

               •  any command executed asynchronously (i.e., in a background process).

       Creating  processes  is  expensive, so as a performance optimization, a subshell of a non-
       interactive shell may share the process of its parent  environment.  Such  a  subshell  is
       known  as  a  virtual  subshell.  Subshells are virtual unless or until something (such as
       asynchronous execution, or an attempt to set a process limit  using  the  ulimit  built-in
       command,  or  other  implementation- or system-defined requirements) makes it necessary to
       fork it into a separate process.  Barring any bugs in the shell, virtual subshells  should
       be indistinguishable from real subshells except by their execution speed and their process
       ID.  See the description of the .sh.pid variable below for more information.

   Command Substitution.
       The standard output from a command list enclosed in parentheses preceded by a dollar  sign
       (  $(list) ), or in a brace group preceded by a dollar sign ( ${ list;} ), or in a pair of
       grave accents (``) may be used as part or all of a word; trailing new-lines  are  removed.
       In the second case, the { and } are treated as a reserved words so that { must be followed
       by a blank and } must appear at the beginning of the line or follow a  ;.   In  the  third
       (obsolete) form, the string between the quotes is processed for special quoting characters
       before the command is executed (see Quoting below).  The command substitution $(cat  file)
       can  be  replaced  by the equivalent but faster $(<file).  The command substitution $(n<#)
       will expand to the current byte offset for file descriptor n.  Except for the second form,
       the  command  list  is  run  in  a subshell so that no side effects are possible.  For the
       second form, the final } will be recognized as a reserved word after any token.

   Arithmetic Expansion.
       An arithmetic expression enclosed in double parentheses preceded by a dollar sign (  $(())
       ) is replaced by the value of the arithmetic expression within the double parentheses.

   Process Substitution.
       Each  command argument of the form <(list) or >(list) will run process list asynchronously
       connected to some file in /dev/fd if this directory exists, or else a fifo in a  temporary
       directory.   The  name  of this file will become the argument to the command.  If the form
       with > is selected then writing on this file will provide input for list.  If <  is  used,
       then  the  file  passed  as  an argument will contain the output of the list process.  For
       example,

              paste <(cut -f1 file1) <(cut -f3 file2) | tee >(process1) >(process2)

       cuts fields 1 and 3 from the files  file1  and  file2  respectively,  pastes  the  results
       together,  and sends it to the processes process1 and process2, as well as putting it onto
       the standard output.  Note that the file, which is passed as an argument to  the  command,
       is a UNIX pipe(2) so programs that expect to lseek(2) on the file will not work.

       Process  substitution of the form <(list) can also be used with the < redirection operator
       which causes the output of list to be standard  input  or  the  input  for  whatever  file
       descriptor is specified.

   Parameter Expansion.
       A  parameter is a variable, one or more digits, or any of the characters *, @, #, ?, -, $,
       and !.  A variable is denoted by a vname.  To create a variable whose vname contains a  .,
       a  variable  whose  vname  consists of everything before the last . must already exist.  A
       variable has a value and zero or more attributes.  Variables can be  assigned  values  and
       attributes by using the typeset special built-in command.  The attributes supported by the
       shell are described later with the typeset special built-in command.   Exported  variables
       pass  their  attributes  to the environment so that a newly invoked ksh that is a child or
       exec'd process of the current shell will automatically import them, unless the posix shell
       option is on.

       The  shell  supports both indexed and associative arrays.  An element of an array variable
       is referenced by a subscript.   A  subscript  for  an  indexed  array  is  denoted  by  an
       arithmetic  expression  (see  Arithmetic Evaluation below) between a [ and a ].  To assign
       values to an indexed array, use vname=(value ...) or set -A vname  value ... .  The  value
       of  all  non-negative  subscripts must be in the range of 0 through 4,194,303.  A negative
       subscript is treated as an offset from the maximum current index +1 so that -1  refers  to
       the  last element.  Indexed arrays can be declared with the -a option to typeset.  Indexed
       arrays need not be declared.  Any reference to a variable with a valid subscript is  legal
       and an array will be created if necessary.

       An  associative  array  is  created  with  the  -A  option to typeset.  A subscript for an
       associative array is denoted by a string enclosed between [ and ].

       Referencing any array without a subscript is equivalent  to  referencing  the  array  with
       subscript 0.

       The value of a variable may be assigned by writing:

              vname=value [ vname=value ] ...

       or

              vname[subscript]=value [ vname[subscript]=value ] ...

       Note that no space is allowed before or after the =.

       Attributes  assigned  by the typeset special built-in command apply to all elements of the
       array.  An array element can be a  simple  variable,  a  compound  variable  or  an  array
       variable.  An element of an indexed array can be either an indexed array or an associative
       array.  An element of an associative array can also be  either.   To  refer  to  an  array
       element  that  is  part  of  an array element, concatenate the subscript in brackets.  For
       example, to refer to the foobar element of an associative array that  is  defined  as  the
       third element of the indexed array, use ${vname[3][foobar]}

       A  nameref  is  a  variable that is a reference to another variable.  A nameref is created
       with the -n attribute of typeset.  The value of the variable at the time  of  the  typeset
       command  becomes  the  variable  that  will be referenced whenever the nameref variable is
       used.  The name of a nameref cannot contain  a  ..   When  a  variable  or  function  name
       contains a ., and the portion of the name up to the first . matches the name of a nameref,
       the variable referred to is obtained by replacing the nameref portion with the name of the
       variable  referenced  by  the nameref.  If a nameref is used as the index of a for loop, a
       name reference is established for each item in the list.  A nameref provides a  convenient
       way  to  refer  to the variable inside a function whose name is passed as an argument to a
       function.  For example, if the name of a variable is passed as the  first  argument  to  a
       function, the command

              typeset -n var=$1

       inside  the  function  causes  references  and  assignments  to  var  to be references and
       assignments to the variable whose name has been passed to the function.

       If any of the floating point attributes, -E, -F, or -X, or the integer attribute,  -i,  is
       set for vname, then the value is subject to arithmetic evaluation as described below.

       Positional parameters, parameters denoted by a number, may be assigned values with the set
       special built-in command.  Parameter $0 is set  from  argument  zero  when  the  shell  is
       invoked.

       The character $ is used to introduce substitutable parameters.

       ${parameter}
              The  shell  reads  all the characters from ${ to the matching } as part of the same
              word even if it contains braces or metacharacters.   The  value,  if  any,  of  the
              parameter  is substituted.  The braces are required when parameter is followed by a
              letter, digit, or underscore that is not to be interpreted as  part  of  its  name,
              when  the variable name contains a ..  The braces are also required when a variable
              is subscripted unless it is part of  an  Arithmetic  Expression  or  a  Conditional
              Expression.   If parameter is one or more digits then it is a positional parameter.
              A positional parameter of more than one digit  must  be  enclosed  in  braces.   If
              parameter  is  *  or  @,  then all the positional parameters, starting with $1, are
              substituted (separated by a field separator character).  If  an  array  vname  with
              last subscript * @, or for indexed arrays of the form sub1 ..  sub2.  is used, then
              the value for each of the elements between sub1 and sub2 inclusive (or all elements
              for * and @) is substituted, separated by the first character of the value of IFS.

       ${#parameter}
              If  parameter  is  *  or  @,  the  number  of positional parameters is substituted.
              Otherwise, the length of the value of the parameter is substituted.

       ${#vname[*]}
       ${#vname[@]}
              The number of elements in the array vname is substituted.

       ${@vname}
              Expands to the type name (See Type Variables  below) or attributes of the  variable
              referred to by vname.

       ${!vname}
              Expands  to  the  name  of  the  variable referred to by vname.  This will be vname
              except when vname is a name reference.

       ${!vname[subscript]}
              Expands to name of the subscript unless subscript is *, @.  or of the form sub1  ..
              sub2.   When  subscript  is *, the list of array subscripts for vname is generated.
              For a variable that is not an array, the  value  is  0  if  the  variable  is  set.
              Otherwise  it is the empty string.  When subscript is @, same as above, except that
              when used in double quotes, each array subscript yields a separate argument.   When
              subscript is of the form sub1 ..  sub2 it expands to the list of subscripts between
              sub1 and sub2 inclusive using the same quoting rules as @.

       ${!prefix@}
       ${!prefix*}
              These both expand to the names of the variables whose names begin with prefix.  The
              expansions otherwise work like $@ and $*, respectively (see under Quoting below).

       ${parameter:-word}
              If parameter is set and has a non-empty value, then substitute its value; otherwise
              substitute word.

       ${parameter:=word}
              If parameter is not set or has the empty string value, then set  it  to  word;  the
              value  of  the  parameter  is  then  substituted.  Positional parameters may not be
              assigned to in this way.

       ${parameter:?word}
              If parameter is  set  and  has  a  non-empty  value,  then  substitute  its  value;
              otherwise,  print  word  and  exit from the shell (if not interactive).  If word is
              omitted then a standard message is printed.

       ${parameter:+word}
              If parameter is set and has a  non-empty  value  then  substitute  word;  otherwise
              substitute the empty string.

       In  the above, word is not evaluated unless it is to be used as the substituted string, so
       that, in the following example, pwd is executed only if d is not  set  or  has  the  empty
       string value:

              print ${d:-$(pwd)}

       If the colon (:) is omitted from the above expressions, then the shell only checks whether
       parameter is set or not.

       ${parameter:offset:length}
       ${parameter:offset}
              Expands to the portion  of  the  value  of  parameter  starting  at  the  character
              (counting  from  0)  determined by expanding offset as an arithmetic expression and
              consisting of the number of characters  determined  by  the  arithmetic  expression
              defined  by  length.  In the second form, the remainder of the value is used.  If A
              negative offset counts backwards from the end of parameter.  Note that one or  more
              blanks  is required in front of a minus sign to prevent the shell from interpreting
              the operator as :-.  If parameter is * or @, or is an array name indexed by * or @,
              then   offset  and  length  refer  to  the  array  index  and  number  of  elements
              respectively.  A negative offset is taken relative to one greater than the  highest
              subscript for indexed arrays.  The order for associative arrays is unspecified.

       ${parameter#pattern}
       ${parameter##pattern}
              If  the  shell  pattern  matches  the beginning of the value of parameter, then the
              value of this expansion is the value of the  parameter  with  the  matched  portion
              deleted;  otherwise  the value of this parameter is substituted.  In the first form
              the smallest matching pattern is  deleted  and  in  the  second  form  the  largest
              matching  pattern  is  deleted.   When parameter is @, *, or an array variable with
              subscript @ or *, the substring operation is applied to each element in turn.

       ${parameter%pattern}
       ${parameter%%pattern}
              If the shell pattern matches the end of the value of parameter, then the  value  of
              this  expansion  is  the  value  of  the  parameter  with the matched part deleted;
              otherwise substitute the value of  parameter.   In  the  first  form  the  smallest
              matching  pattern is deleted and in the second form the largest matching pattern is
              deleted.  When parameter is @, *, or an array variable with subscript @ or  *,  the
              substring operation is applied to each element in turn.

       ${parameter/pattern/string}
       ${parameter//pattern/string}
       ${parameter/#pattern/string}
       ${parameter/%pattern/string}
              Expands  parameter and replaces the longest match of pattern with the given string.
              Each occurrence of \n in string is  replaced  by  the  portion  of  parameter  that
              matches  the  n-th  subpattern.   In  the  first form, only the first occurrence of
              pattern is replaced.  In the second form, each match for pattern is replaced by the
              given  string.   The third form restricts the pattern match to the beginning of the
              string while the fourth form restricts the pattern match to the end of the  string.
              When  string is empty, the pattern will be deleted and the / in front of string may
              be omitted.  When parameter is @, *, or an array variable with subscript  @  or  *,
              the  substitution  operation is applied to each element in turn.  In this case, the
              string portion of word will be re-evaluated for each element.

   Shell Variables.
       The following parameters are automatically set by the shell:
              #      The number of positional parameters in decimal.

              -      Options supplied to the shell on invocation or by the set command.

              ?      The exit status returned by the last executed command. Its  meaning  depends
                     on  the  command or function that defines it, but there are conventions that
                     other commands often depend on: zero typically means  'success'  or  'true',
                     one  typically  means 'non-success' or 'false', and a value greater than one
                     typically indicates some kind of error. Only the 8 least significant bits of
                     $?  (values  0  to 255) are preserved when the exit status is passed on to a
                     parent process, but within the same (sub)shell environment, it is  a  signed
                     integer  value  with  a  range  of  possible values as shown by the commands
                     getconf INT_MIN and getconf INT_MAX. Shell functions that run in the current
                     environment may return status values in this range.

              $      The  process  ID  of  the  main shell process. Note that this value will not
                     change in a subshell, even if the subshell runs in a different process.  See
                     also .sh.pid.

              _      Initially,  the  value  of  _ is an absolute pathname of the shell or script
                     being executed as passed in the environment.  Subsequently  it  is  assigned
                     the  last  argument  of the previous command.  This parameter is not set for
                     commands which are asynchronous.  This parameter is also used  to  hold  the
                     name  of  the  matching  MAIL file when checking for mail.  While defining a
                     compound variable or a type, _ is initialized as a reference to the compound
                     variable  or  type.  When a discipline function is invoked, _ is initialized
                     as a reference to the variable associated with the call  to  this  function.
                     Finally  when  _  is  used  as  the  name  of  the  first variable of a type
                     definition, the new type is derived from the type  of  the  first  variable.
                     (See Type Variables  below.)

              !      The  process  ID  or  the  pool  name  and job number of the last background
                     command invoked or the most recent job put in the  background  with  the  bg
                     built-in  command.   Background  jobs started in a named pool will be in the
                     form pool.number where pool is the pool name and number is  the  job  number
                     within that pool.

              .sh.command
                     When  processing  a  DEBUG  trap, this variable contains the current command
                     line that is about to run.  The value is in the same format  as  the  output
                     generated by the xtrace option (minus the preceding PS4 prompt).

              .sh.edchar
                     This  variable  contains the value of the keyboard character (or sequence of
                     characters if the first character is  an  ESC,  ASCII  033)  that  has  been
                     entered when processing a KEYBD trap (see Key Bindings below).  If the value
                     is changed as part of the trap action, then the new value replaces  the  key
                     (or key sequence) that caused the trap.

              .sh.edcol
                     The  character  position  of the cursor at the time of the most recent KEYBD
                     trap.

              .sh.edmode
                     Upon executing a KEYBD trap action, the value of this variable is set to the
                     ESC control character if the shell is in vi insert mode (See Vi Editing Mode
                      below), or to the empty string value otherwise.

              .sh.edtext
                     The characters in the input buffer at the time  of  the  most  recent  KEYBD
                     trap.  The variable is unset when not processing a KEYBD trap.

              .sh.file
                     The pathname of the file that contains the current command.

              .sh.fun
                     The name of the current function that is being executed.

              .sh.level
                     Set  to the current call depth of functions and dot scripts.  Normally, this
                     variable is read-only, but while executing a DEBUG trap, its  value  may  be
                     changed  to switch the current function scope to that of the specified level
                     for the duration of the trap run, making it  possible  to  access  a  parent
                     scope  for  debugging  purposes.  When trap execution ends, the variable and
                     the scope are restored.  It is an error to assign a value lower than 0  (the
                     global scope) or higher than the current call depth.

              .sh.lineno
                     Set during a DEBUG trap to the line number for the caller of each function.

              .sh.match
                     An  indexed  array which stores the most recent match and subpattern matches
                     after conditional pattern matches that match and after variables  expansions
                     using  the operators #, %, or /.  The 0-th element stores the complete match
                     and the i-th.  element stores the i-th submatch.  For //, the array is  two-
                     dimensional,  with  the first subscript indicating the most recent match and
                     subpattern match, and the second subscript indicating  which  match  with  0
                     representing the first match.  The .sh.match variable becomes unset when the
                     variable that has expanded is assigned a new value.

              .sh.math
                     Used for defining arithmetic functions (see Arithmetic Evaluation below) and
                     stores the list of user defined arithmetic functions.

              .sh.name
                     Set  to  the  name of the variable at the time that a discipline function is
                     invoked.

              .sh.subscript
                     Set to the name subscript of the variable at  the  time  that  a  discipline
                     function is invoked.

              .sh.subshell
                     The current depth for subshells and command substitution.

              .sh.pid
                     Set  to  the  process  ID  of the current shell process.  Unlike $$, this is
                     updated in a subshell when it forks into a new process.  Note that a virtual
                     subshell  may  have  to  fork  mid-execution  due  to  various  system-  and
                     implementation-dependent requirements, so the value should not be counted on
                     to remain the same from one command to the next.  If a persistent process ID
                     is required for a subshell, it must be ensured it  is  running  in  its  own
                     process first.  Any attempt to set a process limit using the ulimit built-in
                     command, such as ulimit -t unlimited 2>/dev/null, is a reliable way to  make
                     a subshell fork if it hasn't already.

              .sh.ppid
                     Set  to  the  process ID of the parent of the current shell process.  Unlike
                     $PPID, this is updated in a subshell when it forks into a new process.   The
                     same note as for .sh.pid applies.

              .sh.value
                     Set  to  the  value  of  the  variable  at  the  time that the set or append
                     discipline function is invoked.  When a user defined arithmetic function  is
                     invoked, the value of .sh.value is saved and .sh.value is set to long double
                     precision floating point.  .sh.value is restored when the function returns.

              .sh.version
                     Set to a value that identifies the version of this shell.

              COLUMNS
                     Width of the terminal window in character positions.  Updated  automatically
                     at  initialization  and  on receiving a SIGWINCH signal.  The shell uses the
                     value to define the width of the edit window for the shell  edit  modes  and
                     for printing select lists.

              KSH_VERSION
                     A name reference to .sh.version.

              LINENO The current line number within the script or function being executed.

              LINES  Height   of   the  terminal  window  in  lines.   Updated  automatically  at
                     initialization and on receiving a SIGWINCH signal.  The shell uses the value
                     to  determine  the column length for printing select lists: they are printed
                     vertically until about two thirds of LINES lines are filled.

              OLDPWD The previous working directory set by the cd command.

              OPTARG The value of the last option argument  processed  by  the  getopts  built-in
                     command.

              OPTIND The  index  of  the  last  option argument processed by the getopts built-in
                     command.

              PPID   The process ID of the parent of the main  shell  process.   Note  that  this
                     value  will  not  change  in  a  subshell,  even  if  the subshell runs in a
                     different process.  See also .sh.ppid.

              PWD    The present working directory set by the cd command.

              RANDOM Each  time  this  variable  is  referenced,  a  random  integer,   uniformly
                     distributed  between  0  and  32767,  is  generated.  The sequence of random
                     numbers can be initialized by assigning a numeric value to RANDOM.

              REPLY  This variable is set by the  select  statement  and  by  the  read  built-in
                     command when no arguments are supplied.

              SECONDS
                     Each  time  this  variable  is referenced, the number of seconds since shell
                     invocation is returned.  If this variable is  assigned  a  value,  then  the
                     value  returned  upon reference will be the value that was assigned plus the
                     number of seconds since the assignment.

              SHLVL  An integer variable that is incremented and exported each time the shell  is
                     invoked.   If  SHLVL is not in the environment when the shell is invoked, it
                     is set to 1.

       The following variables are used by the shell:
              CDPATH The search path for the cd command.

              EDITOR If the VISUAL variable is not set,  the  value  of  this  variable  will  be
                     checked  for  certain  patterns and the corresponding editing option will be
                     turned on as described with VISUAL below.

              ENV    If this variable is set, then parameter expansion, command substitution, and
                     arithmetic  expansion are performed on the value to generate the pathname of
                     the script that will be executed when the  shell  is  invoked  interactively
                     (see  Invocation below).  This file is typically used for alias and function
                     definitions.  The default value is $HOME/.kshrc.  On systems that support  a
                     system  wide   /etc/ksh.kshrc initialization file, if the filename generated
                     by  the  expansion  of  ENV  begins  with  /./  or  ././  the  system   wide
                     initialization file will not be executed.

              FCEDIT Obsolete  name  for the default editor name for the hist command.  FCEDIT is
                     not used when HISTEDIT is set.

              FIGNORE
                     A pattern that defines the set  of  filenames  that  will  be  ignored  when
                     performing filename matching.

              FPATH  The  search path for function definitions.  The directories in this path are
                     searched for a file with the same name as the function  or  command  when  a
                     function  with  the  -u  attribute  is  referenced and when a command is not
                     found.  If an executable file with the name of that command is  found,  then
                     it  is  read  and  executed  in  the  current environment.  Unlike PATH, the
                     current directory must be  represented  explicitly  by  .   rather  than  by
                     adjacent : characters or a beginning or ending :.

              histchars
                     This  variable  can  be  used  to  specify up to three ASCII characters that
                     control  history  expansion  (see  History  Expansion  below).   The   first
                     (default: !) signals the start of a history expansion.  The second (default:
                     ^) is used for short-form substitutions.  The third (default: #), when found
                     as the first character of a word, causes history expansion to be skipped for
                     the rest of the words on the line.  Multi-byte characters (e.g.  UTF-8)  are
                     not supported and produce undefined results.

              HISTCMD
                     Number of the current command in the history file.

              HISTEDIT
                     Name for the default editor name for the hist command.

              HISTFILE
                     If  this  variable  is  set when the shell is invoked, then the value is the
                     pathname of the file that will be used to store  the  command  history  (see
                     Command Re-entry below).

              HISTSIZE
                     If  this  variable  is  set  when  the  shell is invoked, then the number of
                     previously entered commands that  are  accessible  by  this  shell  will  be
                     greater than or equal to this number.  The default is 512.

              HOME   The default argument (home directory) for the cd command.

              IFS    Internal  field  separators, normally space, tab, and new-line that are used
                     to separate the results of command substitution or parameter  expansion  and
                     to  separate  fields with the built-in command read.  The first character of
                     the IFS variable is used to separate arguments for the "$*"  expansion  (see
                     Quoting below).  Each single occurrence of an IFS character in the string to
                     be split that is not in  the  isspace  character  class,  and  any  adjacent
                     characters  in IFS that are in the isspace character class, delimit a field.
                     One or more characters in IFS that belong to  the  isspace  character  class
                     delimit  a  field.   In  addition,  if  the  same  isspace character appears
                     consecutively inside IFS  and  the  posix  shell  option  is  not  on,  this
                     character  is  treated as if it were not in the isspace class - for example,
                     if IFS consists of two tab characters,  then  two  adjacent  tab  characters
                     delimit an empty field.

              JOBMAX This  variable  defines  the maximum number running background jobs that can
                     run at a time.  When this limit is reached, the shell will wait for a job to
                     complete before starting a new job.

              LANG   This   variable   determines  the  locale  category  for  any  category  not
                     specifically selected with a variable starting with LC_ or LANG.

              LC_ALL This variable overrides the value of the LANG variable  and  any  other  LC_
                     variable.

              LC_COLLATE
                     This  variable  determines  the  locale  category  for  character  collation
                     information.

              LC_CTYPE
                     This  variable  determines  the  locale  category  for  character   handling
                     functions.   It  determines  the character classes for pattern matching (see
                     Pathname Expansion below).

              LC_NUMERIC
                     This  variable  determines  the  locale  category  for  the  decimal   point
                     character.

              MAIL   If this variable is set to the name of a mail file and the MAILPATH variable
                     is not set, then the shell informs the  user  of  arrival  of  mail  in  the
                     specified file.

              MAILCHECK
                     This  variable  specifies  how  often  (in seconds) the shell will check for
                     changes in the modification time of  any  of  the  files  specified  by  the
                     MAILPATH  or  MAIL  variables.   The default value is 600 seconds.  When the
                     time has elapsed the shell will check before issuing the next prompt.

              MAILPATH
                     A colon ( : ) separated list of file names.  If this variable is  set,  then
                     the  shell informs the user of any modifications to the specified files that
                     have occurred within the last MAILCHECK seconds.   Each  file  name  can  be
                     followed  by  a  ?   and  a  message that will be printed.  The message will
                     undergo parameter expansion, command substitution, and arithmetic  expansion
                     with  the variable $_ defined as the name of the file that has changed.  The
                     default message is you have mail in $_.

              PATH   The search path for commands (see Execution below).  The user may not change
                     PATH if executing under rksh (except in .profile).

              PS1    Every  time a new command line is started on an interactive shell, the value
                     of this variable  is  expanded  to  resolve  backslash  escaping,  parameter
                     expansion,  command  substitution,  and  arithmetic  expansion.   The result
                     defines the primary prompt string for that command line.  The default is ``$
                     ''.   The  character  !   in  the  primary  prompt string is replaced by the
                     command number (see Command Re-entry below).  Two successive occurrences  of
                     !   will  produce  a single !  when the prompt string is printed.  Note that
                     any terminal escape sequences  used  in  the  PS1  prompt  thus  need  every
                     instance of !  in them to be changed to !!.

              PS2    Secondary prompt string, by default ``> ''.

              PS3    Selection prompt string used within a select loop, by default ``#? ''.

              PS4    The  value  of  this  variable is expanded for parameter evaluation, command
                     substitution,  and  arithmetic  expansion  and  precedes  each  line  of  an
                     execution trace.  By default, PS4 is ``+ ''.  In addition when PS4 is unset,
                     the execution trace prompt is also ``+ ''.

              SHELL  The pathname of the shell is kept in the environment.  At invocation, if the
                     basename  of  this  variable  is  rsh, rksh, or krsh, then the shell becomes
                     restricted.

              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 a format sequence that is expanded
                     to  a  time  value  or  other  information.   The format sequences and their
                     meanings are as follows.
                     %%        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 brackets denote optional portions.  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 can be displayed; values of p greater than 3
                     are treated as 3.  If p is not specified, the value 3 is used.

                     The optional l specifies a longer format, including hours  if  greater  than
                     zero,  minutes,  and  seconds  of  the  form  HHhMMmSS.FFs.   The value of p
                     determines whether or not the fraction is included.  Seconds are zero-padded
                     unless the posix shell option is on.

                     All  other  characters  are  output without change and a trailing newline is
                     added.     If    the    variable    is    unset,    the    default    value,
                     $'\nreal\t%2lR\nuser\t%2lU\nsys\t%2lS',  is used.  If the value is empty, no
                     timing information is displayed.

              TMOUT  Terminal read timeout. If set to a value greater than zero, the read  built-
                     in command and the select compound command time out after TMOUT seconds when
                     input is from a terminal.  An interactive shell will  issue  a  warning  and
                     allow  for  an  extra 60 second timeout grace period before terminating if a
                     line is not entered within the prescribed number of  seconds  while  reading
                     from  a terminal.  (Note that the shell can be compiled with a maximum bound
                     for this value which cannot be exceeded.)

              VISUAL The value of this variable is scanned when the shell is invoked and whenever
                     its  value  is  changed;  if  it  is  found  to  match certain patterns, the
                     corresponding line editor (see In-line Editing Options below) is  activated.
                     If it matches the pattern *[Vv][Ii]*, the vi option is turned on; else if it
                     matches the pattern *gmacs*, the gmacs option  is  turned  on;  else  if  it
                     matches  the  pattern *macs*, the emacs option is turned on.  If none of the
                     patterns  match,  emacs  is  turned  on  by  default  upon  initializing  an
                     interactive  shell.   If  the value is changed by assignment and none of the
                     patterns match, no options are changed.  The value of VISUAL  overrides  the
                     value of EDITOR.

       The  shell  gives default values to PATH, PS1, PS2, PS3, PS4, MAILCHECK, FCEDIT, TMOUT and
       IFS, while HOME, SHELL, ENV, histchars, and MAIL are not set at all by the shell (although
       HOME is set by login(1)).  On some systems MAIL and SHELL are also set by login(1).

   Field Splitting.
       After  parameter  expansion  and  command  substitution,  the results of substitutions are
       scanned for the field separator characters (those found in IFS) and  split  into  distinct
       fields  where  such  characters are found.  Explicit empty fields ("" or ′′) are retained.
       Implicit empty fields (those resulting from parameters that are unset or have empty string
       values  or  from  command substitutions yielding the empty string, and that are not quoted
       with "") are removed.

   Brace Expansion.
       If the braceexpand (-B) option is set then each of  the  fields  resulting  from  IFS  are
       checked  to  see  if  they  contain  one  or  more of the brace patterns {*,*}, {l1..l2} ,
       {n1..n2} , {n1..n2% fmt} , {n1..n2 ..n3} , or {n1..n2 ..n3%fmt} , where *  represents  any
       character, l1,l2 are letters and n1,n2,n3 are signed numbers and fmt is a format specified
       as used by printf.  In each case, fields are created by prepending the  characters  before
       the  {  and  appending  the characters after the } to each of the strings generated by the
       characters between the { and }.  The resulting fields are checked to see if they have  any
       brace patterns.

       In  the  first  form, a field is created for each string between { and ,, between , and ,,
       and between , and }.  The string represented by * can contain embedded matching  {  and  }
       without quoting.  Otherwise, each { and } with * must be quoted.

       In  the  seconds  form,  l1  and  l2  must both be either upper case or both be lower case
       characters in the C locale.  In this case a field is created for each  character  from  l1
       through l2.

       In  the  remaining forms, a field is created for each number starting at n1 and continuing
       until it reaches n2 incrementing n1 by n3.  The cases where n3 is not specified behave  as
       if  n3  where 1 if n1<=n2 and -1 otherwise.  If forms which specify %fmt any format flags,
       widths and precisions can be specified and fmt can end in any of the  specifiers  cdiouxX.
       For  example,  {a,z}{1..5..3%02d}{b..c}x  expands  to  the  8 fields, a01bx, a01cx, a04bx,
       a04cx, z01bx, z01cx, z04bx and z04cx.

   Pathname Expansion.
       This is also known as globbing or sometimes  filename  generation.   Following  splitting,
       each field is scanned for the characters *, ?, (, and [ unless the -f option has been set.
       If one of these characters appears, then the word is regarded as  a  pattern.   Each  file
       name  component  that  contains any pattern character is replaced with a lexicographically
       sorted set of names that matches the pattern from that directory.   If  no  file  name  is
       found  that  matches  the  pattern,  then that component of the filename is left unchanged
       unless the pattern is prefixed with ∼(N), in which case it is removed as described  below.
       The  special  traversal  names .  and ..  are never matched.  If FIGNORE is set, then each
       file name component that matches the pattern defined by the value of  FIGNORE  is  ignored
       when  generating  the  matching filenames.  If FIGNORE is not set, the character .  at the
       start of each file name component will be  ignored  unless  the  first  character  of  the
       pattern  corresponding  to this component is the character .  itself.  Note that, for uses
       of pattern matching other than pathname expansion, the / and .  are not treated specially.

              *      Matches any string, including the empty  string.   When  used  for  filename
                     expansion, if the globstar option is on, an isolated pattern of two adjacent
                     *s will match all files and zero or more directories and subdirectories.  If
                     followed by a / then only directories and subdirectories will match.
              ?      Matches any single character.
              [...]  Matches  any one of the enclosed characters.  A pair of characters separated
                     by - matches any character lexically between the pair,  inclusive.   If  the
                     first character following the opening [ is a !  or ^, then any character not
                     enclosed is matched.  A - can be included in the character set by putting it
                     as the first or last character.
                     Within  [  and  ],  character  classes  can  be  specified  with  the syntax
                     [:class:], where class is one of the following classes defined in the ANSI C
                     standard (note that word is equivalent to alnum plus the character _):
                     alnum  alpha  blank  cntrl  digit  graph  lower print punct space upper word
                     xdigit
                     Within [ and ], an equivalence class can be specified with the syntax  [=c=]
                     which  matches  all  characters  with  the same primary collation weight (as
                     defined by the current  locale)  as  the  character  c.   Within  [  and  ],
                     [.symbol.]  matches the collating symbol symbol.

       A  pattern-list is a list of one or more patterns separated from each other with a & or |.
       A & signifies that all patterns must be matched whereas | requires that only  one  pattern
       be  matched.   Composite  patterns  can  be  formed  with  one  or  more  of the following
       subpatterns:
              ?(pattern-list)
                     Optionally matches any one 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.
              {n}(pattern-list)
                     Matches n occurrences of the given patterns.
              {m,n}(pattern-list)
                     Matches from m to n occurrences of the given patterns.  If m is  omitted,  0
                     will be used.  If n is omitted, at least m occurrences will be matched.
              @(pattern-list)
                     Matches exactly one of the given patterns.
              !(pattern-list)
                     Matches anything except one of the given patterns.

       By  default,  each pattern or subpattern will match the longest string possible consistent
       with generating the longest overall match.  If more than one match is  possible,  the  one
       starting closest to the beginning of the string will be chosen.   However, for each of the
       above compound patterns, a - can be inserted in front of the ( to cause the shortest match
       to the specified pattern-list to be used.

       When  pattern-list  is  contained within parentheses, the backslash character \ is treated
       specially even when  inside  a  character  class.    All  ANSI  C  character  escapes  are
       recognized and match the specified character.  In addition, the following escape sequences
       are recognized:
              \d     Matches any character in the digit class.
              \D     Matches any character not in the digit class.
              \s     Matches any character in the space class.
              \S     Matches any character not in the space class.
              \w     Matches any character in the word class.
              \W     Matches any character not in the word class.

       A pattern of the form %(pattern-pair(s)) is a subpattern that can be used to match  nested
       character  expressions.  Each pattern-pair is a two-character sequence that cannot contain
       & or |.  The first pattern-pair specifies the  starting  and  ending  characters  for  the
       match.   Each  subsequent pattern-pair represents the beginning and ending characters of a
       nested group that will be  skipped  over  when  counting  starting  and  ending  character
       matches.   The  behavior  is  unspecified  when  the  first character of a pattern-pair is
       alphanumeric, except for the following:
              D      Causes the ending character to terminate the search for this pattern without
                     finding a match.
              E      Causes the ending character to be interpreted as an escape character.
              L      Causes  the ending character to be interpreted as a quote character, causing
                     all characters to be ignored when looking for a match.
              Q      Causes the ending character to be interpreted as a quote character,  causing
                     all  characters  other  than any escape character to be ignored when looking
                     for a match.

       Thus, %({}Q"E\), matches characters starting at { until  the  matching  }  is  found,  not
       counting  any  {  or  }  that  is  inside a double-quoted string or preceded by the escape
       character \.  Without the {}, this pattern matches any C language string.

       Each subpattern in a composite pattern is numbered, starting at 1, by the location of  the
       (  within  the pattern.  The sequence \n, where n is a single digit and \n comes after the
       nth subpattern, matches the same string as the subpattern itself.

       Finally, a pattern can contain subpatterns  of  the  form  ∼(options:pattern-list),  where
       either options or :pattern-list can be omitted.  Unlike the other compound patterns, these
       subpatterns are not counted in the numbered subpatterns.  :pattern-list  must  be  omitted
       for options F, G, N, and V below.  If options is present, it can consist of one or more of
       the following:
              +      Enable the following options.  This is the default.
              -      Disable the following options.
              E      The remainder of the pattern uses extended regular  expression  syntax  like
                     the -E option of the grep(1) command.
              F      The  remainder of the pattern uses the fixed pattern syntax of the -F option
                     of the grep(1) command.
              G      The remainder of the pattern uses basic regular expression syntax  like  the
                     grep(1) command without options.
              K      The  remainder  of  the  pattern  uses  shell  pattern  syntax.  This is the
                     default.
              N      When it is the first letter and is used  with  pathname  expansion,  and  no
                     matches  occur,  the  file  pattern  expands  to the empty string instead of
                     remaining unexpanded.  Otherwise, it is ignored.
              X      The remainder of the pattern uses augmented regular expression  syntax  like
                     the -X option of the AT&T AST version of the grep(1) command.
              P      The  remainder  of  the pattern uses perl(1) regular expression syntax.  Not
                     all perl regular expression syntax is currently implemented.
              V      The remainder of the pattern uses System V regular expression syntax.
              i      Always treat the match as case-insensitive, regardless of the globcasedetect
                     shell option.
              g      File the longest match (greedy).  This is the default.
              l      Left-anchor the pattern.  This is the default for K style patterns.
              r      Right-anchor the pattern.  This is the default for K style patterns.

       If  both options and :pattern-list are specified, then the options apply only to  pattern-
       list.  Otherwise, these options remain in effect until they are disabled by  a  subsequent
       ∼(...) or at the end of the subpattern containing ∼(...).

   Quoting.
       Each of the metacharacters listed earlier (see Definitions above) has a special meaning to
       the shell and causes termination of a word unless  quoted.   A  character  may  be  quoted
       (i.e., made to stand for itself) by preceding it with a \.  The pair \new-line is removed.
       All characters enclosed between a pair of single quote marks (′′) that is not preceded  by
       a  $  are quoted.  A single quote cannot appear within the single quotes.  A single quoted
       string preceded by an unquoted $  is  processed  as  an  ANSI  C  string  except  for  the
       following:
              \0     Causes the remainder of the string to be ignored.
              \E     Equivalent to the escape character (ASCII 033),
              \e     Equivalent to the escape character (ASCII 033),
              \cx    Expands to the character control-x.
              \C[.name.]
                     Expands to the collating element name.

       Inside  double quote marks (""), parameter and command substitution occur and \ quotes the
       characters \, `, ", and $.  A $ in front of a double quoted string will be ignored in  the
       "C" or "POSIX" locale, and may cause the string to be replaced by a locale specific string
       otherwise.  The meaning of $* and $@ is identical when  not  quoted  or  when  used  as  a
       variable  assignment  value  or as a file name.  However, when used as a command argument,
       "$*" is equivalent to "$1d$2d...", where d is the first character  of  the  IFS  variable,
       whereas  "$@" is equivalent to "$1" "$2" ....  Inside grave quote marks (``), \ quotes the
       characters \, `, and $.  If the grave quotes occur  within  double  quotes,  then  \  also
       quotes the character ".

       The  special  meaning of reserved words or aliases can be removed by quoting any character
       of the reserved word.  The recognition of function names or built-in command names  listed
       below cannot be altered by quoting them.

   Arithmetic Evaluation.
       The  shell  performs  arithmetic  evaluation  for  arithmetic  expansion,  to  evaluate an
       arithmetic command, to evaluate an indexed array subscript, and to evaluate  arguments  to
       the  built-in  commands  shift  and  let as well as arguments to numeric format specifiers
       given to print -f  and printf.  Evaluations are performed using double precision  floating
       point  arithmetic  or  long  double precision floating point for systems that provide this
       data type.  Floating point constants follow the ANSI C programming language floating point
       conventions.   The  case-insensitive  floating  point constants NaN and Inf can be used to
       represent "not a number" and infinity respectively, unless the posix shell option  is  on.
       Integer  constants  follow  the  ANSI  C programming language integer constant conventions
       although only single byte character constants are recognized and character casts  are  not
       recognized.   In  addition  constants  can be of the form [base#]n where base is a decimal
       number between two and sixty-four representing the arithmetic base and n is  a  number  in
       that  base.   The digits above 9 are represented by the lower case letters, the upper case
       letters, @, and _ respectively.  For bases less than or equal to 36, upper and lower  case
       characters can be used interchangeably.

       An arithmetic expression uses the same syntax, precedence, and associativity of expression
       as the C language.  All the C language operators that apply to floating  point  quantities
       can  be used.  In addition, the operator ** can be used for exponentiation.  It has higher
       precedence than multiplication and is left associative.  In addition, when the value of an
       arithmetic  variable or subexpression can be represented as a long integer, all C language
       integer arithmetic operations can be performed.   Variables  can  be  referenced  by  name
       within  an  arithmetic  expression  without  using the parameter expansion syntax.  When a
       variable is referenced, its value is evaluated as an arithmetic expression.

       Any of the following math library functions that are in the C math  library  can  be  used
       within an arithmetic expression:

       abs  acos acosh asin asinh atan atan2 atanh cbrt ceil copysign cos cosh erf erfc exp exp10
       exp2 expm1 fabs fdim finite float floor fma fmax fmin fmod fpclass fpclassify hypot  ilogb
       int  isfinite  isgreater  isgreaterequal isinf isinfinite isless islessequal islessgreater
       isnan isnormal issubnormal isunordered iszero j0 j1 jn ldexp lgamma log log10  log1p  log2
       logb nearbyint nextafter nexttoward pow remainder rint round scalb scalbn signbit sin sinh
       sqrt tan tanh tgamma trunc y0 y1 yn

       In addition, arithmetic functions can be defined as shell functions with a variant of  the
       function name syntax,

       function .sh.math.name ident ... { list ;}
              where  name  is  the  function  name  used  in  the  arithmetic expression and each
              identifier, ident is a name reference to the long double precision  floating  point
              argument.   The  value  of .sh.value when the function returns is the value of this
              function.  User defined functions can take up to 3 arguments and  override  C  math
              library functions.

       An  internal  representation  of  a  variable  as a double precision floating point can be
       specified with the -E [n], -F [n], or -X  [n]  option  of  the  typeset  special  built-in
       command.   The  -E  option  causes  the  expansion  of  the  value to be represented using
       scientific notation when it is expanded.  The  optional  option  argument  n  defines  the
       number  of significant figures.  The -F option causes the expansion to be represented as a
       floating decimal number when it is expanded.  The -X option causes  the  expansion  to  be
       represented  using  the  %a  format  defined  by ISO C-99.  The optional option argument n
       defines the number of places after the decimal (or radix) point in this case.

       An internal integer representation of a variable can be specified with the -i  [n]  option
       of  the  typeset  special  built-in  command.  The optional option argument n specifies an
       arithmetic base to be used when  expanding  the  variable.   If  you  do  not  specify  an
       arithmetic base, base 10 will be used.

       Arithmetic  evaluation is performed on the value of each assignment to a variable with the
       -E, -F, -X, or -i attribute.  Assigning a floating point number to a variable  whose  type
       is an integer causes the fractional part to be truncated.

   Prompting.
       When  used  interactively,  the shell prompts with the value of PS1 after expanding it for
       parameter expansion, command substitution, and  arithmetic  expansion,  before  reading  a
       command.   In addition, each single !  in the prompt is replaced by the command number.  A
       !!  is required to place !  in the prompt.  If at any time a new-line is typed and further
       input  is needed to complete a command, then the secondary prompt (i.e., the value of PS2)
       is issued.

   Conditional Expressions.
       A conditional expression is used with the [[ compound command to test attributes of  files
       and  to  compare strings.  Field splitting and pathname expansion are not performed on the
       words between [[ and ]].  Each expression can be constructed  from  one  or  more  of  the
       following unary or binary expressions:
              string Same as -n string below.
              -a file
                     Same as -e below.  This is obsolete.
              -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 an ordinary file.
              -g file
                     True if file exists and it has its setgid bit set.
              -k file
                     True if file exists and it has its sticky bit set.
              -n string
                     True if length of string is non-zero.
              -o ?option
                     True if option named option is a valid option name.
              -o option
                     True if option named option is on.
              -p file
                     True if file exists and is a fifo special file or a pipe.
              -r file
                     True if file exists and is readable by current process.
              -s file
                     True if file exists and has size greater than zero.
              -t fildes
                     True if file descriptor number fildes is open and associated with a terminal
                     device.
              -u file
                     True if file exists and it has its setuid bit set.
              -v name
                     True if variable name is a valid variable name and is set.
              -w file
                     True if file exists and is writable by current process.
              -x file
                     True if file exists and is executable by current process.   If  file  exists
                     and  is  a  directory,  then  true  if the current process has permission to
                     search in the directory.
              -z string
                     True if length of string is zero.
              -L file
                     True if file exists and is a symbolic link.
              -h file
                     True if file exists and is a symbolic link.
              -N file
                     True if file exists and the modification  time  is  greater  than  the  last
                     access time.
              -O file
                     True if file exists and is owned by the effective user ID of this process.
              -G file
                     True  if  file  exists  and its group matches the effective group ID of this
                     process.
              -R name
                     True if variable name is a name reference.
              -S file
                     True if file exists and is a socket.
              file1 -nt file2
                     True if file1 exists and file2 does not, or file1 is newer than file2.
              file1 -ot file2
                     True if file2 exists and file1 does not, or file1 is older than file2.
              file1 -ef file2
                     True if file1 and file2 exist and refer to the same file.
              string == pattern
                     True if string matches pattern.  Any part of pattern can be quoted to  cause
                     it  to  be  matched  as a string.  With a successful match to a pattern, the
                     .sh.match array variable will contain the match and subpattern matches.
              string = pattern
                     Same as == above, but is obsolete.
              string != pattern
                     True if string does not match pattern.  When the string matches the  pattern
                     the .sh.match array variable will contain the match and subpattern matches.
              string =∼ ere
                     True  if string matches the pattern ∼(E)ere where ere is an extended regular
                     expression.
              string1 < string2
                     True if  string1  comes  before  string2  based  on  ASCII  value  of  their
                     characters.
              string1 > string2
                     True  if  string1  comes  after  string2  based  on  ASCII  value  of  their
                     characters.

       The following obsolete arithmetic comparisons are also permitted:
              exp1 -eq exp2
                     True if exp1 is equal to exp2.
              exp1 -ne exp2
                     True if exp1 is not equal to exp2.
              exp1 -lt exp2
                     True if exp1 is less than exp2.
              exp1 -gt exp2
                     True if exp1 is greater than exp2.
              exp1 -le exp2
                     True if exp1 is less than or equal to exp2.
              exp1 -ge exp2
                     True if exp1 is greater than or equal to exp2.

       In each of the above expressions, if file is of the form /dev/fd/n, where n is an integer,
       then the test is applied to the open file whose descriptor number is n.

       A  compound  expression  can  be  constructed  from  these  primitives by using any of the
       following, listed in decreasing order of precedence:
              (expression)
                     True if expression is true.  Used to group expressions.
              ! expression
                     True if expression is false.
              expression1 && expression2
                     True if expression1 and expression2 are both true.
              expression1 || expression2
                     True if either expression1 or expression2 is true.

   Input/Output.
       Before a command is executed, its input and output  may  be  redirected  using  a  special
       notation  interpreted by the shell.  The following may appear anywhere in a simple-command
       or may precede or follow a command and are not passed on to the invoked command.   Command
       substitution,  parameter expansion, and arithmetic expansion occur before word or digit is
       used except as noted below.  Pathname expansion occurs only if the  shell  is  interactive
       and the pattern matches a single file.  Field splitting is not performed.

       In  each  of  the  following  redirections,  if  file  is of the form /dev/sctp/host/port,
       /dev/tcp/host/port, or /dev/udp/host/port, where host is a hostname or host  address,  and
       port  is  a service given by name or an integer port number, then the redirection attempts
       to make a tcp, sctp or udp connection to the corresponding socket.

       No intervening space is allowed between the characters of redirection operators.

       <word         Use file word as standard input (file descriptor 0).

       >word         Use file word as standard output (file descriptor 1).  If the file does  not
                     exist  then  it is created.  If the file exists, and the noclobber option is
                     on, this causes an error; otherwise, it is truncated to zero length.

       >|word        Same as >, except that it overrides the noclobber option.

       >;word        Write output to a temporary file.  If  the  command  completes  successfully
                     rename  it  to word, otherwise, delete the temporary file.  >;word cannot be
                     used with the exec and redirect built-ins.

       >>word        Use file word as standard output.   If  the  file  exists,  then  output  is
                     appended to it (by first seeking to the end-of-file); otherwise, the file is
                     created.

       <>word        Open file word for reading and writing as standard  output.   If  the  posix
                     option is active, it defaults to standard input instead.

       <>;word       The  same  as <>word except that if the command completes successfully, word
                     is truncated to the offset at command completion.  <>;word  cannot  be  used
                     with the exec and redirect built-ins.

       <<[-]word     The  shell  input  is  read  up to a line that is the same as word after any
                     quoting has been removed, or to an  end-of-file.   No  parameter  expansion,
                     command   substitution,   arithmetic  expansion  or  pathname  expansion  is
                     performed on word.  The resulting document, called a here-document,  becomes
                     the   standard  input.   If  any  character  of  word  is  quoted,  then  no
                     interpretation is placed upon the characters  of  the  document;  otherwise,
                     parameter  expansion,  command substitution, and arithmetic expansion occur,
                     \new-line is ignored, and \ must be used to quote the characters  \,  $,  `.
                     If  -  is  appended  to <<, then all leading tabs are stripped from word and
                     from the document.  If # is appended to <<, then  leading  spaces  and  tabs
                     will  be stripped off the first line of the document and up to an equivalent
                     indentation will be stripped from the remaining lines and from word.  A  tab
                     stop  is assumed to occur at every 8 columns for the purposes of determining
                     the indentation.

       <<<word       A short form of here document in which word  becomes  the  contents  of  the
                     here-document  after  any  parameter  expansion,  command  substitution, and
                     arithmetic expansion occur.

       <&digit       The standard input is duplicated from file descriptor digit (see dup(2)).

       >&digit       The standard output is duplicated from file descriptor digit.

       <&digit-      The file descriptor given by digit is moved to standard input.

       >&digit-      The file descriptor given by digit is moved to standard output.

       <&-           The standard input is closed.

       >&-           The standard output is closed.

       <&p           The input from the co-process is moved to standard input.

       >&p           The output to the co-process is moved to standard output.

       <#((expr))    Evaluate arithmetic expression expr and position file descriptor  0  to  the
                     resulting value bytes from the start of the file.  The variables CUR and EOF
                     evaluate to the current offset  and  end-of-file  offset  respectively  when
                     evaluating expr.

       >#((offset))  The same as <# except applies to file descriptor 1.

       <#pattern     Seeks forward to the beginning of the next line containing pattern.

       <##pattern    The same as <# except that the portion of the file that is skipped is copied
                     to standard output.

       If one of the above is preceded by a digit, with  no  intervening  space,  then  the  file
       descriptor  number referred to is that specified by the digit (instead of the default 0 or
       1).  If one of the above, other than >&- and the ># and <# forms, is preceded by {varname}
       with no intervening space, then a file descriptor number > 9 will be selected by the shell
       and stored in the variable varname, so it can be read from or written to with redirections
       like  <& $varname or >& $varname.  If >&- or the any of the ># and <# forms is preceded by
       {varname} the value of varname defines the file descriptor  to  close  or  position.   For
       example:

              ... 2>&1

       means  file  descriptor  2 is to be opened for writing as a duplicate of file descriptor 1
       and

              exec {n}<file

       means open file named file for reading and store the file descriptor number in variable n.

       A special shorthand redirection operator &>word is available; it is  equivalent  to  >word
       2>&1.  It  cannot be preceded by any digit or variable name. This shorthand is disabled if
       the posix shell option is active.

       The order in which redirections are specified is significant.  The  shell  evaluates  each
       redirection in terms of the (file descriptor, file) association at the time of evaluation.
       For example:

              ... 1>fname 2>&1

       first associates file descriptor 1 with file fname.  It then associates file descriptor  2
       with  the  file  associated  with  file  descriptor  1  (i.e.   fname).   If  the order of
       redirections were reversed, file descriptor  2  would  be  associated  with  the  terminal
       (assuming  file descriptor 1 had been) and then file descriptor 1 would be associated with
       file fname.

       If a command is followed by & and job control is not active,  then  the  default  standard
       input  for  the  command  is the empty file /dev/null.  Otherwise, the environment for the
       execution of a command contains the file descriptors of the invoking shell as modified  by
       input/output specifications.

   Environment.
       The  environment  (see  environ(7))  is  a  list  of name-value pairs that is passed to an
       executed program in the same way as a normal argument list.  The names must be identifiers
       and the values are character strings.  The shell interacts with the environment in several
       ways.  On invocation, the shell scans the environment and creates a variable for each name
       found,  giving  it the corresponding value and attributes and marking it export.  Executed
       commands inherit the environment.  If the user modifies the values of these  variables  or
       creates  new  ones,  using  the  export  or  typeset  -x commands, they become part of the
       environment.  The environment seen by any executed command is thus composed of  any  name-
       value pairs originally inherited by the shell, whose values may be modified by the current
       shell, plus any additions which must be noted in export or typeset -x commands.

       The environment for any simple-command or function may be augmented by prefixing  it  with
       one  or  more  variable assignments.  A variable assignment argument is a word of the form
       identifier=value.  Thus:

              TERM=450 cmd args                  and
              (export TERM; TERM=450; cmd args)

       are equivalent (as far as the above execution of  cmd  is  concerned  except  for  special
       built-in commands listed below - those that are marked with ).

       If  the  obsolete  -k  option  is set, all variable assignment arguments are placed in the
       environment, even if they occur after the command name.  The following first prints a=b  c
       and then c:

              echo a=b c
              set -k
              echo a=b c

       This  feature is intended for use with scripts written for early versions of the shell and
       its use in new scripts is strongly discouraged.  It is likely to disappear someday.

   Functions.
       For historical reasons, there are two ways to define functions, the name() syntax and  the
       function  name  syntax, described in the Commands section above.  Shell functions are read
       in and stored internally.  Alias names are resolved when the function is read.   Functions
       are  executed  like  commands  with  the  arguments passed as positional parameters.  (See
       Execution below.)

       Functions defined by the function name syntax and called  by  name  execute  in  the  same
       process  as  the caller and share all files and present working directory with the caller.
       Traps caught by the caller are reset to their default action inside the function.  A  trap
       condition  that  is not caught or ignored by the function causes the function to terminate
       and the condition to be passed on to the caller.  A trap on EXIT set inside a function  is
       executed  in  the  environment  of  the  caller after the function completes.  Ordinarily,
       variables are shared between the calling program and the function.  However,  the  typeset
       special  built-in  command  used  within  a  function  defines local variables whose scope
       includes the current function.  They can be passed to functions  that  they  call  in  the
       variable assignment list that precedes the call or as arguments passed as name references.
       Errors within functions return control to the caller.

       Functions defined with the name() syntax and functions  defined  with  the  function  name
       syntax  that  are  invoked  with  the  .   special  built-in  are executed in the caller's
       environment and share all variables and  traps  with  the  caller.   Errors  within  these
       function executions cause the script that contains them to abort.

       The special built-in command return is used to return from function calls.

       Function  names  can  be  listed  with the -f or +f option of the typeset special built-in
       command.  The text of functions, when available, will also be listed with  -f.   Functions
       can be undefined with the -f option of the unset special built-in command.

       Ordinarily,  functions  are  unset when the shell executes a shell script.  Functions that
       need to be defined across separate  invocations  of  the  shell  should  be  placed  in  a
       directory and the FPATH variable should contain the name of this directory.  They may also
       be specified in the ENV file.

   Discipline Functions.
       Each variable can have zero or more discipline functions associated with  it.   The  shell
       initially  understands  the  discipline names get, set, append, and unset but can be added
       when defining new types.  On most systems others can be  added  at  run  time  via  the  C
       programming  interface  extension  provided  by  the builtin built-in utility.  If the get
       discipline is defined for a variable,  it  is  invoked  whenever  the  given  variable  is
       referenced.  If the variable .sh.value is assigned a value inside the discipline function,
       the referenced variable will evaluate to this value instead.  If  the  set  discipline  is
       defined for a variable, it is invoked whenever the given variable is assigned a value.  If
       the append discipline is defined for a  variable,  it  is  invoked  whenever  a  value  is
       appended to the given variable.  The variable .sh.value is given the value of the variable
       before invoking the discipline, and the variable will be assigned the value  of  .sh.value
       after  the  discipline  completes.  If .sh.value is unset inside the discipline, then that
       value is unchanged.  If the unset discipline is defined for  a  variable,  it  is  invoked
       whenever the given variable is unset.

       The  variable .sh.name contains the name of the variable for which the discipline function
       is called, .sh.subscript is the subscript of the variable, and .sh.value will contain  the
       value being assigned inside the set discipline function.  The variable _ is a reference to
       the variable including the subscript if any.  For the set discipline,  changing  .sh.value
       will  change  the value that gets assigned.  Finally, the expansion ${var.name}, when name
       is the name of a discipline, and there is no variable of this name, is equivalent  to  the
       command substitution ${ var.name;}.

   Name Spaces.
       Commands  and  functions that are executed as part of the list of a namespace command that
       modify variables or create new ones, create a new variable whose name is the name  of  the
       name  space  as  given by identifier preceded by ..  When a variable whose name is name is
       referenced, it is first  searched  for  using  .identifier.name.   Similarly,  a  function
       defined  by  a command in the namespace list is created using the name space name preceded
       by a ..

       When the list of a namespace command contains a namespace command, the names of  variables
       and  functions  that  are created consist of the variable or function name preceded by the
       list of identifiers each preceded by ..

       Outside of a name space, a variable or  function  created  inside  a  name  space  can  be
       referenced by preceding it with the name space name.

       By default, variables starting with .sh are in the sh name space.

   Type Variables.
       Typed variables provide a way to create data structure and objects.  A type can be defined
       either by a shared library, by the enum built-in command described below, or by using  the
       new  -T  option  of the typeset built-in command.  With the -T option of typeset, the type
       name, specified as an option argument to -T, is set with a  compound  variable  assignment
       that  defines  the  type.   Function  definitions  can appear inside the compound variable
       assignment and these become discipline functions for this  type  and  can  be  invoked  or
       redefined  by  each  instance of the type.  The function name create is treated specially.
       It is invoked for each instance of the type that is  created  but  is  not  inherited  and
       cannot be redefined for each instance.

       When  a type is defined a special built-in command of that name is added.  These built-ins
       are declaration commands and follow the same expansion  rules  as  the  built-in  commands
       described  below  that are marked with a ‡ symbol. These commands can subsequently be used
       inside further type definitions.  The man page for these  commands  can  be  generated  by
       using the --man option or any of the other -- options described with getopts.  The -r, -a,
       -A, -h, and -S options of typeset are permitted with each of these new built-ins.

       An instance of a type is created by invoking  the  type  name  followed  by  one  or  more
       instance  names.  Each instance of the type is initialized with a copy of the subvariables
       except for subvariables that are defined with the -S option.  Variables defined  with  the
       -S  are  shared  by  all instances of the type.  Each instance can change the value of any
       subvariable and can also define new discipline  functions  of  the  same  names  as  those
       defined  by  the  type definition as well as any standard discipline names.  No additional
       subvariables can be defined for any instance.

       When defining a type, if the value of a subvariable is not set and  the  -r  attribute  is
       specified,  it  causes the subvariable to be a required subvariable.  Whenever an instance
       of a type is created, all required subvariables must  be  specified.   These  subvariables
       become read-only in each instance.

       When  unset  is  invoked on a subvariable within a type, and the -r attribute has not been
       specified for this field, the value is reset to the default  value  associative  with  the
       type.   Invoking  unset  on  a type instance not contained within another type deletes all
       subvariables and the variable itself.

       A type definition can be derived from  another  type  definition  by  defining  the  first
       subvariable  name  as _ and defining its type as the base type.  Any remaining definitions
       will be additions and modifications that apply to the new type.  If the new type  name  is
       the same as that of the base type, the type will be replaced and the original type will no
       longer be accessible.

       The typeset command with the -T and no option argument or operands will write all the type
       definitions to standard output in a form that can be read in to create all they types.

   Jobs.
       If  the  monitor option of the set command is turned on, an interactive shell associates a
       job with each pipeline.  It keeps a table of current jobs, printed by  the  jobs  command,
       and  assigns them small integer numbers.  When a job is started asynchronously with &, the
       shell prints a line which looks like:

            [1] 1234

       indicating that the job which was started asynchronously was job  number  1  and  had  one
       (top-level) process, whose process ID was 1234.

       This  paragraph and the next require features that are not in all versions of UNIX and may
       not apply.  If you are running a job and wish to do something else you may hit the key  ^Z
       (control-Z)  which  sends  a STOP signal to the current job.  The shell will then normally
       indicate that the job has  been  `Stopped',  and  print  another  prompt.   You  can  then
       manipulate the state of this job, putting it in the background with the bg command, or run
       some other commands and then eventually bring the job back into the  foreground  with  the
       foreground  command  fg.   A  ^Z takes effect immediately and is like an interrupt in that
       pending output and unread input are discarded when it is typed.

       A job being run in the background will stop  if  it  tries  to  read  from  the  terminal.
       Background jobs are normally allowed to produce output, but this can be disabled by giving
       the command stty tostop.  If you set this tty option, then background jobs will stop  when
       they try to produce output like they do when they try to read input.

       A job pool is a collection of jobs started with list & associated with a name.

       There  are  several  ways  to refer to jobs in the shell.  A job can be referred to by the
       process ID of any process of the job or by one of the following:
              %number
                     The job with the given number.
              pool   All the jobs in the job pool named by pool.
              pool.number
                     The job number number in the job pool named by pool.
              %string
                     Any job whose command line begins with string.
              %?string
                     Any job whose command line contains string.
              %%     Current job.
              %+     Equivalent to %%.
              %-     Previous job.

       In addition, unless noted otherwise, wherever a job  can  be  specified,  the  name  of  a
       background job pool can be used to represent all the jobs in that pool.

       The  shell  learns  immediately whenever a process changes state.  It normally informs you
       whenever a job becomes blocked so that no further progress  is  possible,  but  only  just
       before  it prints a prompt.  This is done so that it does not otherwise disturb your work.
       The notify option of the set command causes the shell to print these job  change  messages
       as soon as they occur.

       When  the  monitor  option is on, each background job that completes triggers any trap set
       for CHLD.

       When you try to leave the shell while jobs are running or stopped, you will be warned that
       `You  have stopped(running) jobs.'  You may use the jobs command to see what they are.  If
       you immediately try to exit again, the shell will not warn you  a  second  time,  and  the
       stopped jobs will be terminated.  When a login shell receives a HUP signal, it sends a HUP
       signal to each job that has not been disowned with the disown built-in  command  described
       below.

   Signals.
       The  INT and QUIT signals for an invoked command are ignored if the command is followed by
       & and the monitor option is not active.  Otherwise, signals have the values  inherited  by
       the shell from its parent (but see also the trap built-in command below).

   Execution.
       Each  time  a command is read, the above expansions and substitutions are carried out.  If
       the command name matches one of the Special Built-in Commands listed below, it is executed
       within  the current shell process.  Next, the command name is checked to see if it matches
       a user defined function.  If it does, the positional parameters are saved and  then  reset
       to  the  arguments of the function call.  A function is also executed in the current shell
       process.  When the function completes or issues a return, the positional parameter list is
       restored.   For  functions  defined  with  the  function name syntax, any trap set on EXIT
       within the function is executed.  The exit value of a function is the value  of  the  last
       command  executed.   If a command name is not a special built-in command or a user defined
       function, but it is one of the built-in commands listed  below,  it  is  executed  in  the
       current shell process.

       The shell variables PATH followed by the variable FPATH defines the list of directories to
       search for the command name.  Alternative directory names are separated by  a  colon  (:).
       The  default  path  is  the  value  that  was  output  by getconf PATH at the time ksh was
       compiled.  The current directory can be specified by two or more adjacent colons, or by  a
       colon  at  the  beginning or end of the path list.  If the command name contains a /, then
       the search path is not used.  Otherwise, each directory in the list of directories defined
       by  PATH  and  FPATH is checked in order.  If the directory being searched is contained in
       FPATH and contains a file whose name matches the command being searched, then this file is
       loaded  into  the  current  shell  environment as if it were the argument to the . command
       except that only preset aliases are expanded, and a function of the given name is executed
       as described above.

       If  this  directory is not in FPATH the shell first determines whether there is a built-in
       version of a command corresponding to a given pathname and if so  it  is  invoked  in  the
       current  process.   If  no  built-in is found, the shell checks for a file named .paths in
       this directory.  If found and there is a line of the form FPATH=path where path  names  an
       existing directory then that directory is searched immediately after the current directory
       as if it were found in the FPATH variable.  If path does not begin with /, it  is  checked
       for relative to the directory being searched.

       The  .paths  file  is then checked for a line of the form PLUGIN_LIB=libname [ : libname ]
       ... .  Each library named by libname will be searched for as if it were an option argument
       to  builtin  -f, and if it contains a built-in of the specified name this will be executed
       instead of a command by this name.  Any built-in loaded from a library found this way will
       be associated with the directory containing the .paths file so it will only execute if not
       found in an earlier directory.

       Finally, the directory will be checked for a file of the given  name.   If  the  file  has
       execute  permission  but is not an a.out file, it is assumed to be a file containing shell
       commands.  A separate shell is spawned to read it.  All non-exported variables are removed
       in  this  case.   If the shell command file doesn't have read permission, or if the setuid
       and/or setgid bits are set on the file, then the shell executes an agent whose job  it  is
       to set up the permissions and execute the shell with the shell command file passed down as
       an open file.  If the .paths contains a line of the form name=value in the first or second
       line, then the environment variable name is modified by prepending the directory specified
       by value to the directory list.  If value is not an absolute directory, then it  specifies
       a  directory  relative to the directory that the executable was found.  If the environment
       variable name does not already exist it will be added to  the  environment  list  for  the
       specified  command.   A  parenthesized  command is executed in a subshell without removing
       non-exported variables.

   Command Re-entry.
       The text of the last HISTSIZE (default 512) commands entered from  a  terminal  device  is
       saved  in  a history file.  The file $HOME/.sh_history is used if the HISTFILE variable is
       not set or if the file it names is not writable.  A shell can access the commands  of  all
       interactive  shells  which use the same named HISTFILE.  The built-in command hist is used
       to list or edit a portion of this file.  The portion of the file to be  edited  or  listed
       can  be  selected by number or by giving the first character or characters of the command.
       A single command or range of commands can be specified.  If you do not specify  an  editor
       program  as  an  argument  to  hist  then  the value of the variable HISTEDIT is used.  If
       HISTEDIT is unset, the obsolete variable FCEDIT is used.  If FCEDIT is not  defined,  then
       /bin/ed is used.  The edited command(s) is printed and re-executed upon leaving the editor
       unless you quit without writing.  The -s option (and in obsolete versions, the editor name
       -)  is  used  to  skip  the  editing  phase and to re-execute the command.  In this case a
       substitution parameter of the form old=new can  be  used  to  modify  the  command  before
       execution.  For example, with the preset alias r, which is aliased to ′hist -s′, typing `r
       bad=good c' will re-execute the most recent  command  which  starts  with  the  letter  c,
       replacing the first occurrence of the string bad with the string good.

   History Expansion.
       History  expansions introduce words from the history list into the input stream, making it
       easy to repeat commands, repeat arguments of a previous command in the current command, or
       fix  typos  in  the previous command.  The history expansion facility is an alternative to
       history control via the fc or hist built-in command.  To enable it,  turn  on  the  -H  or
       histexpand option using the set command (see Built-in Commands below).

       History expansions begin with the character !.  They may begin anywhere in the input.  The
       ! may be preceded by a \ or enclosed in single quotes to prevent its special meaning.  A !
       is  also  passed  unchanged when it is followed by a space, tab, newline, = or (.  History
       expansions do not nest.  They are parsed separately before the shell parser is invoked, so
       they can override shell grammar rules.

       By default, the expanded version of any line that contains a history expansion is printed,
       added to the history, and then immediately executed.  History expansions are  never  added
       to  the  history  themselves,  regardless of whether they succeed or fail due to an error.
       Normally, this means that a command line with an erroneous history expansion is  lost  and
       needs  to  be  retyped from scratch, but if the histreedit shell option is turned on and a
       line editor is active (see In-line Editing Options below),  the  erroneous  line  is  pre-
       filled  into  the next prompt's input buffer for correcting.  The histverify option causes
       the same to be done for successful history expansions, allowing verification  and  editing
       before execution.

       A  history expansion may have an event specification, which indicates the event from which
       words are to be taken, a word designator, which selects particular words from  the  chosen
       event, and/or a modifier, which manipulates the selected words.

       An event specification can be:

           n       A number, referring to a particular event.
           -n      An offset, referring to the event n before the current event.
           #       The current event.
           !       The previous event (equivalent to -1).
           s       The most recent event whose first word begins with the string s.
           ?s?     The  most  recent  event  which  contains  the  string s.  The second ? can be
                   omitted if it is immediately followed by a newline.

       For example, consider this bit of someone's history list as might be output by the hist -l
       command:

           9        nroff -man wumpus.man
           10       cp wumpus.man wumpus.man.old
           11       vi wumpus.man
           12       diff wumpus.man.old wumpus.man

       The  commands  are  shown  with  their event numbers.  The current event, which we haven't
       typed in yet, is event 13.  !11 and !-2 refer to event 11.   !!  refers  to  the  previous
       event,  12.   !!  can  be  abbreviated ! if it is followed by : (see below).  !n refers to
       event 9, which begins with n.  !?old?  also  refers  to  event  12,  which  contains  old.
       Without  word  designators  or  modifiers,  history references simply expand to the entire
       event, so we might type !cp to redo the  copy  command  or  !!|more  if  the  diff  output
       scrolled off the top of the screen.

       To  select  words  from  an  event,  the  event specification can be followed by a : and a
       designator for the desired words.  The words of an input line are  numbered  from  0,  the
       first  word  (usually the command name) being 0, the second word (first argument) being 1,
       etc.  The basic word designators are:

           0       The first word (command name).
           n       The nth argument.
           ^       The first argument, equivalent to 1.
           $       The last argument.
           %       The word matched by the most recent ?s? search.
           x-y     A range of words.
           -y      Equivalent to 0-y.
           *       Equivalent to ^-$, but returns nothing if the event contains only 1 word.
           x*      Equivalent to x-$.
           x-      Equivalent to x*, but omitting the last word ($).

       Selected words are inserted into  the  command  line  separated  by  single  blanks.   For
       example,  the  diff command in the previous example might have been typed as diff !!:1.old
       !!:1 (using :1 to select the first argument from the previous event) or diff  !-2:2  !-2:1
       to  select  and swap the arguments from the cp command.  If we didn't care about the order
       of the diff, we might have said diff !-2:1-2 or simply diff !-2:*.  The cp  command  might
       have  been  written  cp  wumpus.man !#:1.old, using # to refer to the current event.  !n:-
       hurkle.man would reuse the first two words from  the  nroff  command  to  say  nroff  -man
       hurkle.man.

       The  :  separating  the event specification from the word designator can be omitted if the
       argument selector begins with a ^, $, *, % or -.  For example, our diff command might have
       been  diff  !!^.old !!^ or, equivalently, diff !!$.old !!$.  However, if !! is abbreviated
       !, an argument selector beginning with - will be interpreted as an event specification.

       The word(s) in a history reference can be edited  by  following  them  with  one  or  more
       modifiers, each preceded by a colon (:):

           h       Remove a trailing pathname component, leaving the head.
           t       Remove all leading pathname components, leaving the tail.
           r       Remove a filename extension .xxx, leaving the root name.
           e       Remove all but the extension.
           s/l/r/  Substitute  l for r.  l is simply a string like r, not a regular expression as
                   in the eponymous ed(1) command.  Any character may be used as the delimiter in
                   place  of  /;  a  \  can  be  used to quote the delimiter inside l and r.  The
                   character & in the r is replaced by l; \ also quotes &.  If l is empty, the  l
                   from  the  previous  substitution is used, or if there is none, the s from the
                   most recent ?s? search.  The trailing  delimiter  may  be  omitted  if  it  is
                   immediately followed by a newline.
           &       Repeat the previous substitution.
           g       Global  substitution,  for  example  :gs/foo/bar/  or :g&.  Applies the s or &
                   modifier to the entire command line.
           a       Same as g.
           p       Print the new command line but do not execute it.
           q       Quote the expanded words, preventing further expansions.
           x       Like q, but break into words at blanks, tabs and newlines.

       Modifiers are applied to only the first modifiable word (unless g or a is used).  It is an
       error for no word to be modifiable.

       For  example, the diff command might have been written as diff wumpus.man.old !#^:r, using
       :r to remove .old from the first argument on the same line (!#^).  We might follow mail -s
       "I forgot my password" rot with !:s/rot/root to correct the spelling of root.

       History  expansions  also  occur  when  an input line begins with ^.  When it is the first
       character on an input line, it is an abbreviation  of  !:s^.   Thus  we  might  have  said
       ^rot^root  to  make  the  spelling  correction  in the previous example.  This is the only
       history expansion that does not explicitly begin with !.

       If a word on a command line begins with the history comment character #, history expansion
       is  ignored  for  the rest of that line.  This usually causes the shell parser (which uses
       the same character to signal a comment) to treat the rest of the  line  as  a  comment  as
       well,  but  as  history  expansion  is  parsed  separately from the shell grammar and with
       different rules, this cannot be guaranteed in all cases.  If the history comment character
       is changed, the shell grammar comment character does not change along with it.

       The  three  characters used to signal history expansion can be changed using the histchars
       shell variable; see Shell Variables above.

   In-line Editing Options.
       Normally, each command line entered from a terminal device is simply typed followed  by  a
       new-line  (`RETURN'  or `LINE FEED').  If either the emacs, gmacs, or vi option is active,
       the user can edit the command line.  To  be  in  either  of  these  edit  modes,  set  the
       corresponding option.  An editing option is automatically selected each time the VISUAL or
       EDITOR variable is assigned a value matching any of these editor names; for  details,  see
       Shell Variables above under VISUAL.

       The  editing  features require that the user's terminal accept `RETURN' as carriage return
       without line feed and that a space (` ') must  overwrite  the  current  character  on  the
       screen.

       Unless the multiline option is on, the editing modes implement a concept where the user is
       looking through a window at the current line.  The window width is the value of COLUMNS if
       it  is  defined, otherwise 80.  If the window width is too small to display the prompt and
       leave at least 8 columns to enter input, the prompt is truncated from the  left.   If  the
       line  is  longer  than  the  window width minus two, a mark is displayed at the end of the
       window to notify the user.  As the cursor moves and reaches  the  window  boundaries,  the
       window  will  be centered about the cursor.  The mark is a > (<, *) if the line extends on
       the right (left, both) side(s) of the window.

       The search commands in each edit mode provide access to the history  file.   Only  strings
       are matched, not patterns, although a leading ^ in the string restricts the match to begin
       at the first character in the line.

       Each of the edit modes has an operation to  list  the  files  or  commands  that  match  a
       partially  entered  word.   When  applied to the first word on the line, or the first word
       after a ;, |, &, or (, and the word does not begin with  or contain  a  /,  the  list  of
       aliases,  functions, and executable commands defined by the PATH variable that could match
       the partial word is displayed.  Otherwise, the list of files that match the given word  is
       displayed.   If the partially entered word does not contain any file expansion characters,
       a * is appended before generating these lists.  After displaying the generated  list,  the
       input  line  is  redrawn.   These operations are called command name listing and file name
       listing, respectively.  There are additional  operations,  referred  to  as  command  name
       completion and file name completion, which compute the list of matching commands or files,
       but instead of printing the list, replace the current word  with  a  complete  or  partial
       match.  For file name completion, if the match is unique, a / is appended if the file is a
       directory and a space is appended if the file is not a directory.  Otherwise, the  longest
       common  prefix for all the matching files replaces the word.  For command name completion,
       only the portion of the file names after the last / are used to find the  longest  command
       prefix.   If  only  a  single name matches this prefix, then the word is replaced with the
       command name followed by a space.  When using a tab for completion that does not  yield  a
       unique  match,  a subsequent tab will provide a numbered list of matching alternatives.  A
       specific selection can be made by  entering  the  selection  number  followed  by  a  tab.
       Neither  completion  nor  listing operations are attempted before the first character in a
       line.

   Key Bindings.
       The KEYBD trap can be used to intercept keys as they are typed and change  the  characters
       that  are  actually  seen  by  the  shell.  This trap is executed after each character (or
       sequence of characters when the first character is ESC) is entered while  reading  from  a
       terminal.   The  variable  .sh.edchar  contains  the character or character sequence which
       generated the trap.  Changing the value of .sh.edchar in the trap action causes the  shell
       to  behave  as  if  the  new value were entered from the keyboard rather than the original
       value.

       The variable .sh.edcol is set to the input column number of the cursor at the time of  the
       input.   The  variable .sh.edmode is set to ESC when in vi insert mode (see below) and set
       to the empty  string  otherwise.   Prepending  ${.sh.editmode}  to  a  value  assigned  to
       .sh.edchar  will  cause  the  shell to change to control mode if it is not already in this
       mode.

       This trap is not invoked for characters entered as arguments  to  editing  directives,  or
       while reading input for a character search.

   Emacs Editing Mode.
       This  mode  is  entered by enabling either the emacs or gmacs option.  The only difference
       between these two modes is the way they handle ^T.  To edit, the user moves the cursor  to
       the  point  needing  correction and then inserts or deletes characters or words as needed.
       All the editing commands are control characters or escape  sequences.   The  notation  for
       control  characters  is  caret  (^)  followed  by  the  character.  For example, ^F is the
       notation for control F.  This is entered by depressing `f' while holding down  the  `CTRL'
       (control)  key.   The  `SHIFT'  key is not depressed.  (The notation ^?  indicates the DEL
       (delete) key.)

       The notation for escape sequences is  M-  followed  by  a  character.   For  example,  M-f
       (pronounced  Meta f) is entered by depressing ESC (ASCII 033) followed by `f'.  (M-F would
       be the notation for ESC followed by `SHIFT' (capital) `F'.)

       All edit commands operate from any place on the line (not just at the beginning).  Neither
       the `RETURN' nor the `LINE FEED' key is entered after edit commands except when noted.

       The M-[ multi-character commands below are DEC VT220 escape sequences generated by special
       keys on standard PC keyboards, such as the arrow keys.  You could type them  directly  but
       they are meant to recognize the keys in question, which are indicated in parentheses.

       ^F        Move cursor forward (right) one character.
       M-[C      (Right arrow) Same as ^F.
       M-f       Move cursor forward one word.  (The emacs editor's idea of a word is a string of
                 characters consisting of only letters, digits and underscores.)
       M-[1;3C   (Alt-Right arrow) Same as M-f.
       M-[1;5C   (Ctrl-Right arrow) Same as M-f.
       M-[1;9C   (iTerm2 Alt-Right arrow) Same as M-f.
       ^B        Move cursor backward (left) one character.
       M-[D      (Left arrow) Same as ^B.
       M-b       Move cursor backward one word.
       M-[1;3D   (Alt-Left arrow) Same as M-b.
       M-[1;5D   (Ctrl-Left arrow) Same as M-b.
       M-[1;9D   (iTerm2 Alt-Left arrow) Same as M-b.
       ^A        Move cursor to start of line.
       M-[H      (Home) Same as ^A.
       M-[1~     Same as ^A.
       M-[7~     Same as ^A.
       ^E        Move cursor to end of line.
       M-[F      (End) Same as ^E.
       M-[4~     Same as ^E.
       M-[8~     Same as ^E.
       M-[Y      Same as ^E.
       M-OA      (Up Arrow) Same as M-[A.
       M-OB      (Down Arrow) Same as M-[B.
       M-OC      (Right Arrow) Same as M-[C.
       M-OD      (Left Arrow) Same as M-[D.
       M-O5C     (Ctrl-Right Arrow) Same as M-f.
       M-O5D     (Ctrl-Left Arrow) Same as M-b.
       ^]char    Move cursor forward to character char on current line.
       M-^]char  Move cursor backward to character char on current line.
       ^X^X      Interchange the cursor and mark.
       erase     (User defined erase character as defined by the stty(1) command, usually  ^H  .)
                 Delete previous character.
       lnext     (User defined literal next character as defined by the stty(1) command, or ^V if
                 not defined.)  Removes the next character's editing features (if any).
       ^D        Delete current character.
       M-[3~     (Forward delete) Same as ^D.
       M-d       Delete current word.
       M-[3;5~   (Ctrl-Delete) Same as M-d.
       M-^H      (Meta-backspace) Delete previous word.
       M-h       Delete previous word.
       M-^?      (Meta-DEL) Delete previous word (if your interrupt character is  ^?   (DEL,  the
                 default) then this command will not work).
       ^T        Transpose  current  character  with previous character and advance the cursor in
                 emacs mode.  Transpose two previous characters in gmacs mode.
       ^C        Capitalize current character.
       M-c       Capitalize current word.
       M-l       Change the current word to lower case.
       ^K        Delete from the cursor to the end of the  line.   If  preceded  by  a  numerical
                 parameter whose value is less than the current cursor position, then delete from
                 given position up to the cursor.  If preceded by  a  numerical  parameter  whose
                 value is greater than the current cursor position, then delete from cursor up to
                 given cursor position.
       ^W        Kill from the cursor to the mark.
       M-p       Push the region from the cursor to the mark on the stack.
       kill      (User defined kill character as defined by the stty command, usually ^U .)  Kill
                 the  entire current line.  If two kill characters are entered in succession, all
                 kill characters from then  on  cause  a  line  feed  (useful  when  using  paper
                 terminals).  A subsequent pair of kill characters undoes this change.
       ^Y        Restore last item removed from line. (Yank item back to the line.)
       ^L        Line feed and print current line.
       M-^L      Clear the screen.
       ^@        (Null character) Set mark.
       M-space   (Meta space) Set mark.
       ^J        (New line) Execute the current line.
       ^M        (Return) Execute the current line.
       eof       End-of-file  character,  normally ^D, is processed as an End-of-file only if the
                 current line is empty.
       ^P        Fetch previous command.  Each time ^P is entered the previous  command  back  in
                 time  is  accessed.   Moves back one line when not on the first line of a multi-
                 line command.
       M-[A      (Up arrow) If the cursor is at the end of the line, it is equivalent to ^R  with
                 string  set to the contents of the current line.  Otherwise, it is equivalent to
                 ^P.
       M-<       Fetch the least recent (oldest) history line.
       M->       Fetch the most recent (youngest) history line.
       ^N        Fetch next command line.  Each time ^N is entered the next command line  forward
                 in time is accessed.
       M-[B      (Down arrow) Equivalent to ^N.
       ^Rstring  Reverse  search  history  for  a  previous command line containing string.  If a
                 parameter of zero is given, the search is forward.  String is  terminated  by  a
                 `RETURN'  or  `NEW LINE'.   If  string is preceded by a ^, the matched line must
                 begin with string.  If string is omitted, then the next command line  containing
                 the  most  recent string is accessed.  In this case a parameter of zero reverses
                 the direction of the search.
       ^G        Exit reverse search mode.
       ^O        Operate - Execute the current line and fetch the next line relative  to  current
                 line from the history file.
       M-digits  (Escape)  Define  numeric  parameter, the digits are taken as a parameter to the
                 next command.  The commands that accept a parameter are ^F, ^B, erase,  ^C,  ^D,
                 ^K, ^R, ^P, ^N, ^], M-., M-^], M-_, M-=, M-b, M-c, M-d, M-f, M-h, M-l, M-^H, and
                 the arrow keys and forward-delete key.
       M-letter  Soft-key - Your alias list is searched for an alias by the name _letter  and  if
                 an alias of this name is defined, its value will be inserted on the input queue.
                 The letter must not be one of the above meta-functions.
       M-[letter Soft-key - Your alias list is searched for an alias by the name __letter and  if
                 an alias of this name is defined, its value will be inserted on the input queue.
                 This can be used to program function keys on many terminals.
       M-.       The last word of the previous command is inserted on the line.  If preceded by a
                 numeric  parameter,  the value of this parameter determines which word to insert
                 rather than the last word.
       M-_       Same as M-..
       M-*       Attempt pathname expansion on the current word.  An asterisk is appended if  the
                 word doesn't match any file or contain any special pattern characters.
       M-ESC     Command or file name completion as described above.
       ^I tab    Attempts  command  or  file  name  completion  as described above.  If a partial
                 completion occurs, repeating this will behave as if M-=  were  entered.   If  no
                 match is found or entered after space, a tab is inserted.
       M-=       If  not  preceded  by  a  numeric  parameter,  it generates the list of matching
                 commands or file names as described above.  Otherwise, the word under the cursor
                 is replaced by the item corresponding to the value of the numeric parameter from
                 the most recently generated command or file list.  If the cursor  is  not  on  a
                 word, it is inserted instead.
       ^U        Multiply parameter of next command by 4.
       \         If  the  backslashctrl  shell  option is on (which is the default setting), this
                 escapes the next character.  Editing characters,  the  user's  erase,  kill  and
                 interrupt  (normally  ^C)  characters  may  be entered in a command line or in a
                 search string if preceded by a \.  The \ removes the  next  character's  editing
                 features (if any).  See also lnext which is not subject to any shell option.
       M-^V      Display version of the shell.
       M-[2~     (Insert) Escape the next character.
       M-#       If  the  line  does  not begin with a #, a # is inserted at the beginning of the
                 line and after each new-line, and the line is entered.  This causes a comment to
                 be  inserted in the history file.  If the line begins with a #, the # is deleted
                 and one # after each new-line is also deleted.

   Vi Editing Mode.
       There are two typing modes.  Initially, when you enter a command  you  are  in  the  input
       mode.   To  edit, the user enters control mode by typing ESC (033) and moves the cursor to
       the point needing correction and then inserts or deletes characters or  words  as  needed.
       Most control commands accept an optional repeat count prior to the command.

       The notation for control characters used below is ^ followed by a character. For instance,
       ^H is entered by holding  down  the  Control  key  and  pressing  H.   ^[  (Control+[)  is
       equivalent  to  the  ESC  key.  The notation for escape sequences is ^[ followed by one or
       more characters.

       The ^[[ (ESC [) multi-character commands below are DEC VT220 escape sequences generated by
       special  keys  on  standard  PC  keyboards, such as the arrow keys, which are indicated in
       parentheses. When in input mode, these  keys  will  switch  you  to  control  mode  before
       performing  the  associated  action.   These  sequences  can  use  preceding  repeat count
       parameters, but only when the ^[ and the subsequent [ are entered into the input buffer at
       the same time, such as when pressing one of those keys.

        Input Edit Commands
              By default the editor is in input mode.

              erase     (User  defined erase character as defined by the stty command, usually ^H
                        or #.)  Delete previous character.
              ^W        Delete the previous blank separated word.   On  some  systems  the  viraw
                        option may be required for this to work.
              eof       As  the  first character of the line causes the shell to terminate unless
                        the ignoreeof option is set.  Otherwise this character is ignored.
              lnext     (User defined literal next character as defined by the stty(1) or  ^V  if
                        not  defined.)   Removes  the next character's editing features (if any).
                        On some systems the viraw option may be required for this to work.
              \         If the backslashctrl shell option is on (which is the  default  setting),
                        this escapes the next erase or kill character.
              ^I tab    Attempts  command  or file name completion as described above and returns
                        to input mode. If a partial completion occurs, repeating this will behave
                        as  if = were entered from control mode.  If no match is found or entered
                        after space, a tab is inserted.

        Motion Edit Commands
              These commands will move the cursor.

              [count]l  Cursor forward (right) one character.
              [count]^[[C
                        (Right arrow) Same as l.
              [count]w  Cursor forward one alphanumeric word.
              [count]W  Cursor to the beginning of the next word that follows a blank.
              [count]e  Cursor to end of word.
              [count]E  Cursor to end of the current blank delimited word.
              [count]h  Cursor backward (left) one character.
              [count]^[[D
                        (Left arrow) Same as h.
              [count]b  Cursor backward one word.
              [count]B  Cursor to preceding blank separated word.
              [count]|  Cursor to column count.
              [count]fc Find the next character c in the current line.
              [count]Fc Find the previous character c in the current line.
              [count]tc Equivalent to f followed by h.
              [count]Tc Equivalent to F followed by l.
              [count];  Repeats count times, the last single character find command, f, F, t,  or
                        T.
              [count],  Reverses the last single character find command count times.
              0         Cursor to start of line.
              ^[[H      (Home) Same as 0.
              ^[[1~     Same as 0.
              ^[[7~     Same as 0.
              ^[[1;3D   (Alt-Left arrow) Same as b.
              ^[[1;5D   (Ctrl-Left arrow) Same as b.
              ^[[1;9D   (iTerm2 Alt-Left arrow) Same as b.
              ^[[1;3C   (Alt-Right arrow) Same as w.
              ^[[1;5C   (Ctrl-Right arrow) Same as w.
              ^[[1;9C   (iTerm2 Alt-Right arrow) Same as w.
              ^[[2~     (Insert) Same as i.
              ^[[3;5~   (Ctrl-Delete) Same as dw.
              ^[OA      (Up Arrow) Same as ^[[A.
              ^[OB      (Down Arrow) Same as ^[[B.
              ^[OC      (Right Arrow) Same as ^[[C.
              ^[OD      (Left Arrow) Same as ^[[D.
              ^[O5C     (Ctrl-Right Arrow) Same as w.
              ^[O5D     (Ctrl-Left Arrow) Same as b.
              ^         Cursor to first non-blank character in line.
              $         Cursor to end of line.
              ^[[F      (End) Same as $.
              ^[[4~     Same as $.
              ^[[8~     Same as $.
              ^[[Y      Same as $.
              ^G        Exit reverse search mode.
              %         Moves  to  balancing (, ), {, }, [, or ].  If cursor is not on one of the
                        above characters, the remainder of the line is  searched  for  the  first
                        occurrence of one of the above characters first.

        Search Edit Commands
              These commands access your command history.

              [count]k  Fetch previous command.  Each time k is entered the previous command back
                        in time is accessed.
              [count]-  Equivalent to k.
              [count]^[[A
                        (Up arrow) If cursor is at the end of the line it is equivalent to / with
                        string  set  to  the  contents  of  the  current  line.  Otherwise, it is
                        equivalent to k.
              [count]j  Fetch next command.  Each time j is entered the next command  forward  in
                        time is accessed.
              [count]+  Equivalent to j.
              [count]^[[B
                        (Down arrow) Equivalent to j.
              [count]G  The  command  number  count  is fetched.  The default is the least recent
                        history command.
              /string   Search backward through history for a previous command containing string.
                        String  is terminated by a `RETURN' or `NEW LINE'.  If string is preceded
                        by a ^, the matched line must begin with string.  If string is empty, the
                        previous string will be used.
              ?string   Same as / except that search will be in the forward direction.
              n         Search for next match of the last pattern to / or ?  commands.
              N         Search  for  next  match  of  the  last pattern to / or ?, but in reverse
                        direction.

        Text Modification Edit Commands
              These commands will modify the line.

              a         Enter input mode and enter text after the current character.
              A         Append text to the end of the line.  Equivalent to $a.
              [count]cmotion
              c[count]motion
                        Delete current character through the character that motion would move the
                        cursor  to and enter input mode.  If motion is c, the entire line will be
                        deleted and input mode entered.
              C         Delete the current character through the end  of  line  and  enter  input
                        mode.  Equivalent to c$.
              S         Equivalent to cc.
              [count]s  Replace characters under the cursor in input mode.
              D         Delete the current character through the end of line.  Equivalent to d$.
              [count]dmotion
              d[count]motion
                        Delete current character through the character that motion would move to.
                        If motion is d , the entire line will be deleted.
              i         Enter input mode and insert text before the current character.
              I         Insert text before the first non-blank character.  Equivalent to ^i.
              [count]P  Place the previous text modification before the cursor.
              [count]p  Place the previous text modification after the cursor.
              R         Enter input mode and replace characters on the screen with characters you
                        type overlay fashion.
              [count]rc Replace  the  count  character(s) starting at the current cursor position
                        with c, and advance the cursor.
              [count]x  Delete current character.
              [count]^[[3~
                        (Forward delete) Same as x.
              [count]X  Delete preceding character.
              [count].  Repeat the previous text modification command.
              [count]  Invert the case of the count character(s) starting at the current  cursor
                        position and advance the cursor.
              [count]_  Causes  the  count  word of the previous command to be appended and input
                        mode entered.  The last word is used if count is omitted.
              *         Causes an * to be appended to the current  word  and  pathname  expansion
                        attempted.  If no match is found, it rings the bell.  Otherwise, the word
                        is replaced by the matching pattern and input mode is entered.
              \         Command or file name completion as described above.

        Other Edit Commands
              Miscellaneous commands.

              [count]ymotion
              y[count]motion
                        Yank current character through  character  that  motion  would  move  the
                        cursor  to and puts them into the delete buffer.  The text and cursor are
                        unchanged.
              yy        Yanks the entire line.
              Y         Yanks from current position to end of line.  Equivalent to y$.
              u         Undo the last text modifying command.
              U         Undo all the text modifying commands performed on the line.
              [count]v  Returns the command hist -e ${VISUAL:-${EDITOR:-vi}} count in  the  input
                        buffer.  If count is omitted, then the current line is used.
              ^L        Line feed and print current line.  Has effect only in control mode.
              ^J        (New line) Execute the current line, regardless of mode.
              ^M        (Return) Execute the current line, regardless of mode.
              #         If  the  first character of the command is a #, then this command deletes
                        this # and each # that follows a  newline.   Otherwise,  sends  the  line
                        after  inserting  a  #  in front of each line in the command.  Useful for
                        causing the current line to be inserted in the history as a  comment  and
                        uncommenting previously commented commands in the history file.
              [count]=  If  count is not specified, it generates the list of matching commands or
                        file names as described above.  Otherwise, the word under the  cursor  is
                        replaced  by  the  count item from the most recently generated command or
                        file list.  If the cursor is not on a word, it is inserted instead.
              @letter   Your alias list is searched for an alias by the name _letter  and  if  an
                        alias  of  this  name is defined, its value will be inserted on the input
                        queue for processing.
              ^V        Display version of the shell.

   Built-in Commands.
       The simple-commands listed below are built in to the shell and are executed  in  the  same
       process as the shell.  The effects of any added Input/Output redirections are local to the
       command, except for the exec and  redirect  commands.   Unless  otherwise  indicated,  the
       output  is  written on standard output (file descriptor 1) and the exit status, when there
       is no syntax error, is zero.  Except for :, true, false, and echo, all  built-in  commands
       accept -- to indicate end of options, and are self-documenting.

       The  self-documenting  commands  interpret  the  option --man as a request to display that
       command's own manual page, --help as a request to display the OPTIONS section  from  their
       manual page, and -?  as a request to print a brief usage message.  All these are processed
       as error messages, so they are written on standard error (file descriptor 2) and  to  pipe
       them  into  a  pager  such as more(1) you need to add a 2>&1 redirection before the |. The
       display of boldface text depends on whether  standard  error  is  on  a  terminal,  so  is
       disabled when using a pager. Exporting the ERROR_OPTIONS environment variable with a value
       containing emphasis will force this on; a value containing noemphasis forces it off.   The
       test/[  command  needs  an additional -- argument to recognize self-documentation options,
       e.g. test --man --.  The exec and redirect commands, as they make redirections  permanent,
       should  use  self-documentation  options  in  a  subshell  when  redirecting, for example:
       (redirect --man) 2>&1.  There are advanced output options as well; see getopts  --man  for
       more information.

       Commands  that  are  preceded  by  a  † symbol below are special built-in commands and are
       treated specially in the following ways:
              1.     Variable assignment lists preceding the command remain in  effect  when  the
                     command completes.
              2.     I/O redirections are processed after variable assignments.
              3.     Errors cause a script that contains them to abort.
              4.     They are not valid function names.

       Commands  that  are  preceded by a ‡ symbol below are declaration commands.  Any following
       words that are in the format of a variable assignment are expanded with the same rules  as
       a  variable  assignment.   This  means that tilde expansion is performed after the = sign,
       array assignments of the form varname=(assign_list) are supported, and field splitting and
       pathname expansion are not performed.

       † : [ arg ... ]
              The command only expands parameters.

       † . name [ arg ... ]
              If  name  is  a  function  defined with the function name reserved word syntax, the
              function is executed in the current environment (as if it had been defined with the
              name()  syntax).   Otherwise  if  name  refers  to  a file, the file is read in its
              entirety and the commands are executed  in  the  current  shell  environment.   The
              search  path  specified  by PATH is used to find the directory containing the file.
              If any arguments arg  are  given,  they  become  the  positional  parameters  while
              processing  the .  command and the original positional parameters are restored upon
              completion.  Otherwise the positional parameters are unchanged.  The exit status is
              the exit status of the last command executed.

       [ expression ]
              The  [ command is the same as test, with the exception that an additional closing ]
              argument is required. See test below.

       alias [ -ptx ]  [ name[ =value  ] ] ...
              alias with no arguments prints the list  of  aliases  in  the  form  name=value  on
              standard  output.   The  -p option causes the word alias to be inserted before each
              one.  When one or more arguments are given, 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.  With the -t option, each name is looked up  as  a  command  in
              $PATH  and its path is added to the hash table as a 'tracked alias'.  If no name is
              given, this prints the hash table. See hash.  Without the -t option, for each  name
              in  the  argument list for which no value is given, the name and value of the alias
              is printed.  The obsolete -x option has no effect in  most  contexts,  although  if
              it's  used  with  -t it will suppress all output.  The exit status is non-zero if a
              name is given, but no value, and no alias has been defined for the name.

       autoload name ...
              Marks each name undefined so that the FPATH variable will be searched to  find  the
              function definition when the function is referenced.  The same as typeset -fu.

       bg [ job... ]
              This  command is only on systems that support job control.  Puts each specified job
              into the background.  The current job is put  in  the  background  if  job  is  not
              specified.  See Jobs for a description of the format of job.

       † break [ n ]
              Exit  from  the  enclosing  for,  while,  until,  or  select loop, if any.  If n is
              specified, then break n levels.

       builtin [ -ds ] [ -f file ] [ name ... ]
              If name is not specified, and no -f option is specified, the built-ins are  printed
              on  standard  output.  The -s option prints only the special built-ins.  Otherwise,
              each name represents the pathname whose basename is the name of the built-in.   The
              entry  point  function name is determined by prepending b_ to the built-in name.  A
              built-in specified by a pathname will only be executed when that pathname would  be
              found  during  the path search.  Built-ins found in libraries loaded via the .paths
              file will associate with the pathname of the directory containing the .paths file.

              The ISO C/C++ prototype is b_mycommand(int argc, char *argv[], void  *context)  for
              the  builtin  command mycommand where argv is array an of argc elements and context
              is an optional pointer to a Shell_t structure as described in <ast/shell.h>.

              Special built-ins cannot be bound to a pathname or deleted.  The -d option  deletes
              each  of  the  given  built-ins.   On  systems that support dynamic loading, the -f
              option names a shared library  containing  the  code  for  built-ins.   The  shared
              library  prefix  and/or suffix, which depend on the system, can be omitted.  Once a
              library is loaded, its symbols  become  available  for  subsequent  invocations  of
              builtin.   Multiple  libraries  can  be  specified with separate invocations of the
              builtin command.  Libraries are searched in the reverse order  in  which  they  are
              specified.   When a library is loaded, it looks for a function in the library whose
              name is lib_init() and invokes this function with an argument of 0.

       cd [ -L ] [ -eP ] [ arg ]
       cd [ -L ] [ -eP ] old new
              This command can be in either of two forms.  In  the  first  form  it  changes  the
              current  directory  to  arg.   If arg is - the directory is changed to the previous
              directory.  The shell variable HOME is the default arg.  The variable PWD is set to
              the  current  directory.  The shell variable CDPATH defines the search path for the
              directory containing arg.  Alternative directory names are  separated  by  a  colon
              (:).   The  default  path  is  the empty string (specifying the current directory).
              Note that the current directory may be specified by a dot (.)  or by an empty  path
              name,  either  of  which can appear immediately after the equal sign or between the
              colon delimiters anywhere else in the path list.  If arg begins with a /  then  the
              search  path  is  not  used.  Otherwise, each directory in the path is searched for
              arg.
              The second form of cd substitutes the string new for the string old in the  current
              directory name, PWD, and tries to change to this new directory.
              By  default,  symbolic  link names are treated literally when finding the directory
              name.  This is equivalent to the -L option.  The -P option causes symbolic links to
              be  resolved  when determining the directory.  The last instance of -L or -P on the
              command line determines which method is used.
              If -e and -P are both in effect and the correct PWD could not be  determined  after
              successfully  changing  the  directory,  cd  will  return  with exit status one and
              produce no output.  If any other error occurs while both flags are active, the exit
              status is greater than one.
              The cd command may not be executed by rksh.

       command [ -pvxV ] name [ arg ... ]
              With  the -v option, command is equivalent to the built-in whence command described
              below.  The -V option causes command to act like whence -v.

              Without the -v or -V options, command executes name with  the  arguments  given  by
              arg.   Functions  and  aliases will not be searched for when finding name.  If name
              refers to a special built-in, as marked with  in this manual, command disables the
              special  properties  described  above  for  that  mark,  executing the command as a
              regular built-in.  (For example, using command set -o option-name prevents a script
              from terminating when an invalid option name is given.)

              The  -p  option causes the operating system's standard utilities path (as output by
              getconf PATH) to be searched rather than the one defined by the value of PATH.

              The -x option runs name as  an  external  command,  bypassing  built-ins.   If  the
              arguments  contain  at  least  one word that expands to multiple arguments, such as
              "$@" or *.txt, then the -x option also  allows  executing  external  commands  with
              argument lists that are longer than the operating system allows. This functionality
              is similar to xargs(1) but is easier to use. The shell does this  by  invoking  the
              external command multiple times if needed, dividing the expanded argument list over
              the invocations. Any arguments that come before the  first  word  that  expands  to
              multiple  arguments,  as well as any that follow the last such word, are considered
              static arguments and are repeated for each invocation. This allows each  invocation
              to use the same command options, as well as the same trailing destination arguments
              for commands like cp(1) or mv(1).  When all invocations are completed,  command  -x
              exits  with  the  status of the invocation that had the highest exit status.  (Note
              that command -x may still fail with an "argument list too long" error if  a  single
              argument  exceeds  the  maximum length of the argument list, or if a long arguments
              list contains no word that expands to multiple arguments.)

       ‡ compound vname[=value] ...
              Causes each vname to be a compound variable.  The same as typeset -C.

       † continue [ n ]
              Resume the next iteration of the enclosing for, while, until, or select loop.  If n
              is specified, then resume at the n-th enclosing loop.

       disown [ job... ]
              Causes  the shell not to send a HUP signal to each given job, or all active jobs if
              job is omitted, when a login shell terminates.

       echo [ arg ... ]
              When the first arg does not begin with a -, and none of the arguments contain a  \,
              then  echo  prints  each  of its arguments separated by a space and terminated by a
              new-line.  Otherwise, the behavior of echo is system dependent and print or  printf
              described below should be used.  See echo(1) for usage and description.

       ‡ enum [ -i ] type[=(value ...) ] ...
              Creates,  for  each  type  specified, an enumeration type declaration command named
              type.  Variables of the created type can only store any one of  the  values  given.
              For  example,  enum  bool=(false  true)  creates  a  Boolean variable type of which
              variables may be declared like bool x=true y=false.  If  =(value ...)  is  omitted,
              then  type  must  be  an  indexed array variable with at least two elements and the
              values are taken from this array variable.  If -i is specified the values are case-
              insensitive.   Declaration  commands are created as special builtins that cannot be
              removed or overridden by shell functions.  Each created declaration command  has  a
              --man option that shows documentation on its type's behavior and possible values.

              Within  arithmetic  expressions (see Arithmetic Evaluation above), enumeration type
              values translate to index numbers between 0 and the number of defined values  minus
              1.  It  is  an error for an arithmetic expression to assign a value outside of that
              range. Decimal fractions are ignored.  Taking the bool type from the example above,
              if a variable of this type is used in an arithmetic expression, false translates to
              0 and true to 1.  Enumeration values may also be used  directly  in  an  arithmetic
              expression  that  refers  to  a  variable  of an enumeration type.  To continue our
              example, for a bool variable v, ((v==true)) is  the  same  as  ((v==1))  and  if  a
              variable named true exists, it is ignored.

       † eval [ arg ... ]
              The arguments are read as input to the shell and the resulting command(s) executed.

       † exec [ -c ] [ -a name ] [ arg ... ]
              If  arg  is  given,  the command specified by the arguments is executed in place of
              this shell without creating a new process.  The  value  of  the  SHLVL  environment
              variable  is  decreased  by  one,  unless the shell replaced is a subshell.  The -c
              option causes the environment to be cleared before  applying  variable  assignments
              associated  with  the  exec  invocation.  The -a option causes name rather than the
              first arg, to become argv[0] for the new process.  If arg is not given and only I/O
              redirections are given, then this command persistently modifies file descriptors as
              in redirect.exit [ n ]
              Causes the shell to exit with the exit status specified by n.  The  value  will  be
              the  least significant 8 bits of n (if specified) or of the exit status of the last
              command executed.  An end-of-file will also cause the shell to exit, except for  an
              interactive shell that has the ignoreeof option turned on (see set below).

       †‡ export [ -p ] [ name[=value] ] ...
              If  name  is  not  given,  the  names  and  values of each variable with the export
              attribute are printed with the values quoted in a manner that allows them to be re-
              input.   The export command is the same as typeset -x except that if you use export
              within a function, no local variable is created.  The -p  option  causes  the  word
              export  to  be inserted before each one.  Otherwise, the given names are marked for
              automatic export to the environment of subsequently-executed commands.

       false  Does nothing, and exits 1. Used with until for infinite loops.

       fc [ -e ename  ] [ -N num ] [ -nlr ] [ first [ last ] ]
       fc -s  [ old=new ] [ command ]
              The same as hist.

       fg [ job... ]
              This command is only on systems that support job control.  Each  job  specified  is
              brought  to  the  foreground and waited for in the specified order.  Otherwise, the
              current job is brought into the foreground.  See Jobs  for  a  description  of  the
              format of job.

       ‡ float vname[=value] ...
              Declares each vname to be a long floating point number.  The same as typeset -lE.

       functions [ -Stux ] [ name ... ]
              Lists functions.  The same as typeset -f.

       getconf [ name [ pathname ] ]
              Prints  the  current  value  of  the  configuration  parameter  given by name.  The
              configuration parameters are defined by the IEEE POSIX 1003.1 and IEEE POSIX 1003.2
              standards.   (See  pathconf(2)  and sysconf(3).)  The pathname argument is required
              for parameters whose value depends on the location  in  the  file  system.   If  no
              arguments   are  given,  getconf  prints  the  names  and  values  of  the  current
              configuration parameters.  The pathname / is used for each of the  parameters  that
              requires pathname.

       getopts [ -a name ] optstring vname [ arg ... ]
              Checks  arg  for  legal  options.  If arg is omitted, the positional parameters are
              used.  An option argument begins with a + or a -.  An option not beginning  with  +
              or  -  or  the  argument  --  ends  the options.  Options beginning with + are only
              recognized when optstring begins with a +.  optstring  contains  the  letters  that
              getopts  recognizes.   If  a  letter is followed by a :, that option is expected to
              have an argument.  The options can be separated from the argument by  blanks.   The
              option  -?   causes  getopts to generate a usage message on standard error.  The -a
              argument can be used to specify the name  to  use  for  the  usage  message,  which
              defaults to $0.
              getopts  places  the next option letter it finds inside variable vname each time it
              is invoked.  The option letter will be prepended with a + when arg begins with a +.
              The  index  of the next arg is stored in OPTIND.  The option argument, if any, gets
              stored in OPTARG.
              A leading : in optstring causes getopts to store the letter of an invalid option in
              OPTARG,  and  to  set  vname  to  ?  for an unknown option and to : when a required
              option argument is missing.  Otherwise, getopts prints an error message.  The  exit
              status is non-zero when there are no more options.
              There  is  no way to specify any of the options :, +, -, ?, [, and ].  The option #
              can only be specified as the first option.

       hash [ -r ] [ utility ]
              hash displays or modifies the hash  table  with  the  locations  of  recently  used
              programs.  If  given  no  arguments, it lists all command/path associations (a.k.a.
              'tracked aliases') in the hash table. Otherwise, hash performs a  PATH  search  for
              each utility supplied and adds the result to the hash table.  The -r option empties
              the hash table. This can also be achieved by resetting PATH.

       hist [ -e ename  ] [ -N num ] [ -nlr ] [ first [ last ] ]
       hist -s [ old=new ] [ command ]
              In the first form, a range of commands from first to last is selected from the last
              HISTSIZE  commands  that  were typed at the terminal.  The arguments first and last
              may be specified as a number or as a string.  A string is used to locate  the  most
              recent  command  starting  with  the given string.  A negative number is used as an
              offset to the current command number.  If the -l option is selected,  the  commands
              are listed on standard output.  Otherwise, the editor program ename is invoked on a
              file containing these keyboard commands.  If ename is not supplied, then the  value
              of  the  variable  HISTEDIT  is used.  If HISTEDIT is not set, then FCEDIT (default
              /bin/ed) is used as the editor.  When editing is complete, the edited command(s) is
              executed if the changes have been saved.  If last is not specified, then it will be
              set to first.  If first is not specified, the default is the previous  command  for
              editing  and -16 for listing.  The option -r reverses the order of the commands and
              the option -n suppresses command numbers when listing.  In the second form, command
              is  interpreted as first described above and defaults to the last command executed.
              The resulting command is  executed  after  the  optional  substitution  old=new  is
              performed.  The option -N causes hist to start num commands back.

       ‡ integer vname[=value] ...
              Declares each vname to be a long integer number.  The same as typeset -li.

       jobs [ -lnp ] [ job ... ]
              Lists  information about each given job; or all active jobs if job is omitted.  The
              -l option lists process IDs in addition to the normal information.  The  -n  option
              only  displays jobs that have stopped or exited since last notified.  The -p option
              causes only the process group to be listed.  See Jobs  for  a  description  of  the
              format of job.

       kill [ -s signame ] job ...
       kill [ -n signum ] job ...
       kill -Ll [ sig ... ]
              Sends  either  the TERM (terminate) signal or the specified signal to the specified
              jobs or processes.  Signals are either given by number with the  -n  option  or  by
              name  with  the  -s  option (as given in <signal.h>, stripped of the prefix ``SIG''
              with the exception that SIGCLD is named CHLD).  For backward compatibility,  the  n
              and s can be omitted and the number or name placed immediately after the -.  If the
              signal being sent is TERM (terminate) or HUP (hangup), then the job or process will
              be  sent  a  CONT  (continue) signal if it is stopped.  The argument job can be the
              process ID of a process that is not a member of one of the active jobs.   See  Jobs
              for  a description of the format of job.  In the third form, kill -l or kill -L, if
              sig is not specified, the signal names are listed.  The -l option  lists  only  the
              signal  names.   The  -L  option  lists  each signal name and corresponding number.
              Otherwise, for each sig that is a name, the corresponding signal number is  listed.
              For  each  sig  that  is  a  number,  the  signal  name  corresponding to the least
              significant 8 bits of sig is listed.

       let arg ...
              Each arg is a separate arithmetic expression to be evaluated.  let only  recognizes
              octal  numbers  starting with 0 when the set option letoctal is on.  See Arithmetic
              Evaluation above for a description of arithmetic expression evaluation.
              The exit status is 0 if the value  of  the  last  expression  is  non-zero,  and  1
              otherwise.

       ‡ nameref vname[=refname] ...
              Declares each vname to be a variable name reference.  The same as typeset -n.

       print [ -CRenprsv ] [ -u unit ] [ -f format ] [ arg ... ]
              With  no  options  or  with option - or --, each arg is printed on standard output.
              The -f option causes the arguments to be printed as described by printf.   In  this
              case,  any e, n, r, R options are ignored.  Otherwise, unless the -C, -R, -r, or -v
              are specified, the following escape conventions will be applied:
              \a     The alert character (ASCII 07).
              \b     The backspace character (ASCII 010).
              \c     Causes print to end without processing more arguments and not adding a  new-
                     line.
              \f     The formfeed character (ASCII 014).
              \n     The newline character (ASCII 012).
              \r     The carriage return character (ASCII 015).
              \t     The tab character (ASCII 011).
              \v     The vertical tab character (ASCII 013).
              \E     The escape character (ASCII 033).
              \\     The backslash character \.
              \0x    The character defined by the 1, 2, or 3-digit octal string given by x.

              The  -R  option will print all subsequent arguments and options other than -n.  The
              -e causes the above  escape  conventions  to  be  applied.   This  is  the  default
              behavior.   It  reverses  the  effect  of  an earlier -r.  The -p option causes the
              arguments to be written onto the pipe of the process spawned  with  |&  instead  of
              standard  output.   The -v option treats each arg as a variable name and writes the
              value in the printf %B format.  The -C option treats each arg as  a  variable  name
              and  writes the value in the printf %#B format.  The -s option causes the arguments
              to be written onto the history file instead of standard output.  The -u option  can
              be used to specify a one digit file descriptor unit number unit on which the output
              will be placed.  The default is 1.  If the option -n is used, no new-line is  added
              to the output.

       printf [ -v vname ] format [ arg ... ]
              The  arguments  arg  are  printed  on standard output in accordance with the ANSI C
              formatting rules associated with the  format  string  format.   If  the  number  of
              arguments  exceeds the number of format specifications, the format string is reused
              to format remaining arguments.  The following extensions can also be used:
              %b     A %b format can be used instead of %s  to  cause  escape  sequences  in  the
                     corresponding arg to be expanded as described in print.
              %B     A %B option causes each of the arguments to be treated as variable names and
                     the binary value of variable will be printed.  The alternate flag # causes a
                     compound  variable  to  be output on a single line.  This is most useful for
                     compound variables and variables whose attribute is -b.
              %H     A %H format can be used instead of %s to cause characters in  arg  that  are
                     special  in  HTML  and XML to be output as their entity name.  The alternate
                     flag # formats the output for use as a URI.
              %p     A %p format will convert the given number to hexadecimal.
              %P     A %P format can be used instead of %s to cause arg to be interpreted  as  an
                     extended regular expression and be printed as a shell pattern.
              %q     A  %q  format  can be used instead of %s to cause the resulting string to be
                     quoted in a manner than can be reinput to the shell.  When q is preceded  by
                     the alternative format specifier, #, the string is quoted in manner suitable
                     as a field in a .csv format file.
              %(date-format)T
                     A %(date-format)T format can be used to treat an  argument  as  a  date/time
                     string and to format the date/time according to the date-format.
              %Q     A %Q format will convert the given number of seconds to readable time.
              %R     A  %R  format  can be used instead of %s to cause arg to be interpreted as a
                     shell pattern and to be printed as an extended regular expression.
              %Z     A %Z format will output a byte whose value is 0.
              %d     The precision field of the %d format can be followed by a .  and the  output
                     base.  In this case, the # flag character causes base# to be prepended.
              #      The  #  flag,  when used with the %d format without an output base, displays
                     the output in powers of 1000 indicated by one of the following suffixes: k M
                     G  T  P E, and when used with the %i format displays the output in powers of
                     1024 indicated by one of the following suffixes: Ki Mi Gi Ti Pi Ei.
              =      The = flag centers the output within the specified field width.
              L      The L flag, when used with  the  %c  or  %s  formats,  treats  precision  as
                     character width instead of byte count.
              ,      The  , flag, when used with the %d or %f formats, separates groups of digits
                     with the grouping delimiter (, on groups of 3 in the C locale).

              The -v option assigns the output directly to a variable instead of  writing  it  to
              standard  output.  This  is  faster  than  capturing  the  output  using  a command
              substitution and avoids the latter's stripping of final linefeed  characters  (\n).
              The  vname  argument  should  be a valid variable name, optionally with one or more
              array subscripts in square brackets.  Note that square brackets should be quoted to
              avoid pathname expansion.

       pwd [ -LP ]
              Outputs  the value of the current working directory.  The -L option is the default;
              it prints the logical name of the current directory.  If the -P  option  is  given,
              all  symbolic  links  are resolved from the name.  The last instance of -L or -P on
              the command line determines which method is used.

       read [ -ACSaprsv ] [ -d delim ] [ -n n ] [  -N  n  ]  [  -t  timeout  ]  [  -u  unit  ]  [
       vname?prompt ] [ vname ... ]
              The shell input mechanism.  One line is read and is broken up into fields using the
              characters in IFS as separators.  The escape character, \, is used  to  remove  any
              special  meaning for the next character and for line continuation.  The first field
              is assigned to the first vname, the second field to the second  vname,  etc.,  with
              leftover  fields  assigned  to  the last vname.  If vname is omitted, then REPLY is
              used as the default vname.  When vname has the binary attribute and  -n  or  -N  is
              specified,  the  bytes that are read are stored directly into the variable.  If you
              append ?prompt to the first vname, then read will display prompt on standard  error
              before  reading  if standard input is a terminal or pipe; the ? should be quoted to
              protect it from pathname expansion.  The exit status is 0 unless an end-of-file  is
              encountered  or  read has timed out.  The options for the read command have meaning
              as follows:
              -A      Causes the variable vname to be unset and each field that  is  read  to  be
                      stored in successive elements of the indexed array vname.
              -C      Causes  the  variable vname to be read as a compound variable.  Blanks will
                      be ignored when finding the beginning open parenthesis.
              -N      Causes n bytes to be read unless an end-of-file has been encountered or the
                      read times out because of the -t option.
              -S      Causes  the  line to be treated like a record in a .csv format file so that
                      double quotes can be used to allow the delimiter character and the new-line
                      character to appear within a field.
              -a      Same as -A.
              -d      Causes  the read to continue to the first character of delim instead of the
                      newline control character.
              -n      Causes at most n bytes to be read instead of a full line, but  will  return
                      when reading from a slow device as soon as any characters have been read.
              -p      Input  is  read  from the current co-process spawned by the shell using ⎪&.
                      An end-of-file causes read to disconnect the co-process so that another can
                      be created.
              -r      Raw mode. The \ character is not treated specially.
              -s      The input will be saved as a command in the history file.
              -t      Used to specify a timeout in seconds when reading from a terminal or pipe.
              -u      This option can be used to specify a one-digit file descriptor unit unit to
                      read from.  The file descriptor can be opened with  the  exec  or  redirect
                      built-in  command.  If unit is p, input is read from the current co-process
                      as with the -p option.  The default value of unit is 0.
              -v      The value of the first vname will be used as a default value  when  reading
                      from a terminal device.

       †‡ readonly [ -p ] [ vname[=value] ] ...
              If  vname  is  not  given, the names and values of each variable with the read-only
              attribute is printed with the values quoted in a manner that allows them to be  re-
              input.   The  -p  option  causes  the word readonly to be inserted before each one.
              Otherwise, the given vnames are marked read-only and these names cannot be  changed
              by subsequent assignment.  Unlike typeset -r , readonly does not create a function-
              local scope and the given vnames are marked globally read-only  by  default.   When
              defining  a type, if the value of a read-only subvariable is not defined, the value
              is required when creating each instance.

       redirect
              This command only accepts input/output redirections.  It can open and  close  files
              and  modify  file  descriptors  from  0  to  9  as  specified  by  the input/output
              redirection list (see the Input/Output section above), with the difference that the
              effect  persists past the execution of the redirect command.  When invoking another
              program, file descriptors greater than 2 that were opened with this  mechanism  are
              only  passed  on  if  they  are  explicitly redirected to themselves as part of the
              invocation (e.g. 4>&4) or if the posix option is set.

       † return [ n ]
              Causes a shell function, dot script (see . and source), or profile script to return
              to the invoking shell environment with the exit status specified by n.  This status
              value can use the full signed integer  range  as  shown  by  the  commands  getconf
              INT_MIN  and getconf INT_MAX. A value outside that range will produce a warning and
              an exit status of 128.  If n is omitted, then the value of $? is assumed, i.e., the
              exit  status of the last command executed is passed on.  If return is invoked while
              not in a function, dot script, or profile script, then it behaves the same as exit.

       † set [ ±BCGHabefhkmnprstuvx ] [ ±o [ option ] ] ... [ ±A vname ]  [ arg ... ]
              The options for this command have meaning as follows:
              -A      Array assignment.  Unset the variable vname and assign values  sequentially
                      from the arg list.  If +A is used, the variable vname is not unset first.
              -B      Enable brace group expansion. On by default, except if ksh is invoked as sh
                      or rsh.
              -C      Prevents redirection > from truncating  existing  files.   Files  that  are
                      created  are  opened  with the O_EXCL mode.  Requires >| to truncate a file
                      when turned on.
              -G      Enables recursive pathname expansion.  This adds the double-star pattern **
                      to  the  pathname  expansion (see Pathname Expansion above).  By itself, it
                      matches the recursive contents of the current directory, which is  to  say,
                      all  files  and  directories  in  the  current  directory  and  in  all its
                      subdirectories, sub-subdirectories, and so on.   If  the  pathname  pattern
                      ends  in  **/,  only  directories and subdirectories are matched, including
                      symbolic links that point to directories.  A prefixed directory name is not
                      included  in  the  results  unless  that  directory  was  itself found by a
                      pattern. For example, dir/** matches the recursive contents of dir but  not
                      dir  itself,  whereas  di[r]/**  matches  both dir itself and the recursive
                      contents of dir.  Symbolic  links  to  non-directories  are  not  followed.
                      Symbolic  links to directories are followed if they are specified literally
                      or match a pattern as described under Pathname Expansion, but not  if  they
                      result from a double-star pattern.
              -H      Enable  !-style history expansion similar to csh(1).  See History Expansion
                      above.
              -a      All variables that are assigned  a  value  while  this  option  is  on  are
                      automatically  exported,  unless  they have a dot in their name.  Variables
                      created in namespaces declared with the namespace keyword (see Name  Spaces
                      above) are only exported while their name space is active.
              -b      Prints  job  completion  messages as soon as a background job changes state
                      rather than waiting for the next prompt.  If one of the shell line  editors
                      is  in  use  (see In-line Editing Options above), the completion message is
                      inserted directly above the command line being typed.
              -e      Unless contained in a || or && command, or  the  command  following  an  if
                      while  or  until command or in the pipeline following !, if a command has a
                      non-zero exit status, execute the ERR trap, if set, and exit.  This mode is
                      disabled while reading profiles.
              -f      Disables pathname expansion.
              -h      Obsolete; no effect.
              -k      All  variable  assignment  arguments  are  placed  in the environment for a
                      command, not just those that precede the command name.
              -m      Background jobs will run in a separate process group and a line will  print
                      upon  completion.   The  exit  status  of  background jobs is reported in a
                      completion message.  A pipeline will  not  terminate  until  all  component
                      commands  of  the  pipeline  have terminated.  On systems with job control,
                      this option is turned on automatically for interactive shells.
              -n      Read commands and check them for syntax errors, but do  not  execute  them.
                      Ignored for interactive shells.
              -o      The following argument can be one of the following option names:
                      allexport
                              Same as -a.
                      backslashctrl
                              The backslash character \ escapes the next control character in the
                              emacs built-in editor and the next erase or kill character  in  the
                              vi built-in editor.  On by default.
                      bgnice  All  background  jobs  are  run  at  a lower priority.  This is the
                              default mode.
                      braceexpand
                              Same as -B.
                      emacs   Puts you in an emacs style in-line editor for command entry.
                      errexit Same as -e.
                      functrace
                              Causes the -x option's state  and  the  DEBUG  trap  action  to  be
                              inherited  by  functions  defined  using  the function keyword (see
                              Functions above) instead of being reset to default.   Changes  made
                              to  them  within  the  function do not propagate back to the parent
                              scope.  Similarly, this option also causes the DEBUG trap action to
                              be inherited by subshells.
                      globcasedetect
                              When  this  option  is  turned on, globbing (see Pathname Expansion
                              above) and file name listing and completion  (see  In-line  Editing
                              Options   above)  automatically  become  case-insensitive  on  file
                              systems where  the  difference  between  upper-  and  lowercase  is
                              ignored  for  file names. This is transparently determined for each
                              directory, so a path pattern that spans multiple file  systems  can
                              be  part case-sensitive and part case-insensitive.  In more precise
                              terms, each  slash-separated  path  name  component  pattern  p  is
                              treated  as  ~(i:p)  if  its  parent  directory  exists  on a case-
                              insensitive file system.  This option is only present on  operating
                              systems that support case-insensitive file systems.
                      globstar
                              Same as -G.
                      gmacs   Puts you in a gmacs style in-line editor for command entry.
                      histexpand
                              Same as -H.
                      histreedit
                              If a history expansion (see -H) fails, the command line is reloaded
                              into the next prompt's edit buffer, allowing corrections.
                      histverify
                              The results of a history expansion (see  -H)  are  not  immediately
                              executed.   Instead,  the  expanded  line  is  loaded into the next
                              prompt's edit buffer, allowing further changes.
                      ignoreeof
                              An interactive shell will not exit  on  end-of-file.   The  command
                              exit must be used.
                      keyword Same as -k.
                      letoctal
                              The  let  command  allows  octal  numbers  starting  with 0.  On by
                              default if ksh is invoked as sh or rsh.
                      markdirs
                              All directory  names  resulting  from  pathname  expansion  have  a
                              trailing / appended.
                      monitor Same as -m.
                      multiline
                              The  built-in  editors  will  use  multiple lines on the screen for
                              lines that are longer than the width of the screen.  This  may  not
                              work for all terminals.
                      noclobber
                              Same as -C.
                      noexec  Same as -n.
                      noglob  Same as -f.
                      nolog   Obsolete; has no effect.
                      notify  Same as -b.
                      nounset Same as -u.
                      pipefail
                              The  exit  status  of  the entire pipeline will be that of the last
                              component command that exited with a non-zero exit status, or  zero
                              if  no  command exited with a non-zero exit status.  The shell will
                              wait for all component  commands  of  the  pipeline  to  terminate,
                              instead of only waiting for the last component command.
                      posix   Enables  the  POSIX  standard  mode  for maximum compatibility with
                              other compliant shells. At the moment  that  the  posix  option  is
                              turned  on, it also turns on letoctal and turns off -B/braceexpand;
                              the reverse is done when posix is turned back off.  (These  options
                              can still be controlled independently in between.) Furthermore, the
                              posix option is automatically turned  on  upon  invocation  if  the
                              shell  is  invoked  as  sh  or  rsh,  or  if -o posix or --posix is
                              specified on the shell invocation command line, or  when  executing
                              scripts  without  a #! path with this option active in the invoking
                              shell. In that  case,  the  invoked  shell  will  not  import  type
                              attributes  for  variables  (such as integer or left/right justify)
                              from the environment.
                              In addition, while on, the posix option
                              •  disables exporting variable type attributes to  the  environment
                                 for other ksh processes to import;
                              •  if  the -B/braceexpand option is turned back on, disallows brace
                                 expansion on the results of unquoted expansions;
                              •  disables  the  special  handling  of  repeated   isspace   class
                                 characters in the IFS variable;
                              •  causes  file  descriptors  >  2  to  be  left open when invoking
                                 another program;
                              •  disables the &> redirection shorthand;
                              •  disables fast filescan loops of type while inputredirection  ;do
                                 list ;done;
                              •  makes   the  <>  redirection  operator  default  to  redirecting
                                 standard input if no file descriptor number precedes it;
                              •  causes the shell to use a standard UNIX  pipe(2)  instead  of  a
                                 socketpair(2)  to  connect  commands in a pipeline (when reading
                                 directly  from  a  pipeline,  the   <#pattern   and   <##pattern
                                 redirection  operators  will  not  work and the -n option to the
                                 read built-in will not return early when  reading  from  a  slow
                                 device);
                              •  disables  the  special  floating  point constants Inf and NaN in
                                 arithmetic evaluation so that, e.g., $((inf)) and $((nan)) refer
                                 to the variables by those names;
                              •  enables  the  recognition  of  a  leading zero as introducing an
                                 octal number in all arithmetic evaluation  contexts,  except  in
                                 the let built-in while letoctal is off;
                              •  disables  zero-padding  of seconds in the output of the time and
                                 times built-ins;
                              •  stops the . command (but not source) from looking  up  functions
                                 defined with the function syntax;
                              •  disables   the   recognition   of  unexpanded  shell  arithmetic
                                 expressions in the numerical comparison operators -eq, -ne, -gt,
                                 -ge, -lt and -le of the test/[ built-in command, causing them to
                                 accept only decimal numbers as operands;
                              •  changes the test/[ built-in command to make its deprecated expr1
                                 -a  expr2 and expr1 -o expr2 operators work even if expr1 equals
                                 "!" or "(" (which means the nonstandard unary  -a  file  and  -o
                                 option  operators  cannot be directly negated using ! or wrapped
                                 in parentheses); and
                              •  disables a hack that makes test -t ([ -t ]) equivalent  to  test
                                 -t 1 ([ -t 1 ]).
                      privileged
                              Same as -p.
                      showme  When  enabled, simple commands or pipelines preceded by a semicolon
                              (;) will be displayed as if the xtrace option were enabled but will
                              not be executed.  Otherwise, the leading ; will be ignored.
                      trackall
                              Same as -h.
                      verbose Same as -v.
                      vi      Puts  you in insert mode of a vi style in-line editor until you hit
                              the escape character 033.  This puts you in control mode.  A return
                              sends the line.
                      viraw   Each  character  is processed as it is typed in vi mode.  The shell
                              may have been compiled to  force  this  option  on  at  all  times.
                              Otherwise,  canonical  processing (line-by-line input) is initially
                              enabled and the command line will be echoed again if the  speed  is
                              1200 baud or greater and it contains any control characters or less
                              than one second has elapsed since the prompt was printed.  The  ESC
                              character  terminates canonical processing for the remainder of the
                              command and the user can then modify the command line. This  scheme
                              has  the  advantages  of  canonical  processing with the type-ahead
                              echoing of raw mode. If the viraw option is set, the terminal  will
                              always  have  canonical processing disabled.  This mode is implicit
                              for  systems  that  do  not  support  two  alternate  end  of  line
                              delimiters, and may be helpful for certain terminals.
                      xtrace  Same as -x.

                      If  no  option  name  is  supplied,  then  the  current option settings are
                      printed.

              -p      Disables  processing  of  the  $HOME/.profile  file  and  uses   the   file
                      /etc/suid_profile  instead  of  the ENV file.  This mode is on whenever the
                      effective UID (GID) is not equal to the real UID (GID).  Turning  this  off
                      causes the effective UID and GID to be set to the real UID and GID.
              -r      Enables the restricted shell.  This option cannot be unset once set.
              -s      Sort the positional parameters lexicographically.
              -t      (Obsolete).  Exit after reading and executing one command.
              -u      Treat  unset  parameters  as  an  error  when  substituting.  $@ and $* are
                      exempt.
              -v      Print shell input lines as they are read.
              -x      Print commands and their arguments as they are executed.
              --      Do not change any of the options; useful in setting $1 to a value beginning
                      with  -.  If no arguments follow this option then the positional parameters
                      are unset.

              As an obsolete feature, if the first arg is - then the -x and -v options are turned
              off  and  the  next  arg  is  treated as the first argument.  Using + rather than -
              causes these options to be turned  off.   These  options  can  also  be  used  upon
              invocation of the shell.  The current set of options may be found in $-.  Unless -A
              is specified, the remaining arguments are positional parameters and  are  assigned,
              in  order,  to  $1 $2 ....  If no arguments are given, then the names and values of
              all variables are printed on the standard output.

       † shift [ n ]
              The positional parameters from $n+1 ...  are renamed $1 ... , default n is 1.   The
              parameter  n  can  be  any  arithmetic  expression that evaluates to a non-negative
              number less than or equal to $#.

       sleep [ -s ] duration
              Suspends execution for the number of decimal seconds or fractions of a second given
              by duration.  duration can be an integer, floating point value or ISO 8601 duration
              specifying the length of time to sleep.  The option -s causes the sleep builtin  to
              terminate when it receives any signal.  If duration is not specified in conjunction
              with -s, sleep will wait for a signal indefinitely.

       source name [ arg ... ]
              Same as ., except it is not treated as a special built-in command.

       stop job ...
              Sends a SIGSTOP signal to one or more processes specified by job,  suspending  them
              until they receive SIGCONT.  The same as kill -s STOP.

       suspend
              Sends  a  SIGSTOP  signal to the main shell process, suspending the script or child
              shell session until it receives SIGCONT (for instance, when typing fg in the parent
              shell).  Equivalent  to  kill -s STOP "$$",  except that it accepts no operands and
              refuses to suspend a login shell.

       test expression
              The test and [ commands execute conditional expressions similar to those  specified
              for  the  [[ compound command under Conditional Expressions above, but with several
              important differences. The =, == and !=  operators  test  for  string  (in)equality
              without pattern matching; == is nonstandard and unportable. The && and || operators
              are not available. Instead, the -a and -o binary operators can be  used,  but  they
              are  fraught  with pitfalls due to grammatical ambiguities and therefore deprecated
              in favor of invoking separate test commands. Most importantly, as test  and  [  are
              simple  regular  commands,  field splitting and pathname expansion are performed on
              all their arguments and all aspects of regular shell grammar (such as  redirection)
              remain  active.  This  is usually harmful, so care must be taken to quote arguments
              and expansions to avoid this. To avoid the many pitfalls arising from these issues,
              the [[ compound command should be used instead. The primary purpose of the test and
              [ commands is compatibility with other shells that lack [[.

              The test/[ command does not parse options except if there are two arguments and the
              second  is --. To access the inline documentation with an option such as --man, you
              need one of the forms test --man -- or [ --man -- ].

       times  Displays the accumulated user and system CPU times, one line with the times used by
              the  shell  and  another  with those used by all of the shell's child processes. No
              options are supported.  Seconds are zero-padded unless the posix  shell  option  is
              on.

       † trap [ -p ] [ action ] [ sig ] ...
              The  -p option causes the trap action associated with each trap as specified by the
              arguments to be printed  with  appropriate  quoting.   Otherwise,  action  will  be
              processed  as if it were an argument to eval when the shell receives signal(s) sig.
              Each sig can be given as a number or as the name of the signal.  Trap commands  are
              executed in order of signal number.  Any attempt to set a trap on a signal that was
              ignored on entry to the current shell is ineffective.  If action is omitted and the
              first  sig  is a number, or if action is -, then the trap(s) for each sig are reset
              to their original values.  If action is the  empty  string,  then  this  signal  is
              ignored  by  the  shell  and by the commands it invokes.  If sig is ERR then action
              will be executed whenever a command has a non-zero exit status.  If  sig  is  DEBUG
              then  action  will  be executed before each command.  The variable .sh.command will
              contain the current command line when action is running, in the same format as  the
              output  generated  by  the  xtrace option (minus the preceding PS4 prompt).  If the
              exit status of the trap is 2 the command will not be executed.  If the exit  status
              of  the  trap  is  255  and  inside a function or a dot script, the function or dot
              script will return.  If sig is 0 or EXIT and the trap statement is executed  inside
              the  body  of  a  function  defined with the function name syntax, then the command
              action is executed after the function completes.  If sig is 0 or EXIT  for  a  trap
              set  outside  any  function  then  the  command action is executed on exit from the
              shell.  If sig is KEYBD, then action will be executed whenever a key is read  while
              in  emacs,  gmacs, or vi mode.  The trap command with no arguments prints a list of
              commands associated with each signal number.

       An exit or return without an argument in a trap action will preserve the  exit  status  of
       the command that invoked the trap.

       true   Does nothing, and exits 0. Used with while for infinite loops.

       type [ -afpPqt ] name ...
              The same as whence -v.

       †‡  typeset  [  ±ACHSbflmnprstux  ]  [  ±EFLRXZi[n]  ]    [  +-M   [  mapname  ] ] [ -T  [
       tname=(assign_list) ] ] [ -h str ] [ -a [type] ] [ vname[=value ]  ] ...
              Sets attributes and values for shell variables and functions.  When invoked  inside
              a  function  defined  with the function name syntax, a new instance of the variable
              vname is created, and the variable's value and type are restored when the  function
              completes.  The following list of attributes may be specified:
              -A     Declares  vname  to  be an associative array.  Subscripts are strings rather
                     than arithmetic expressions.
              -C     Causes each vname to be a compound  variable.  If  value  names  a  compound
                     variable,  it  is copied into vname.  Otherwise, the empty compound value is
                     assigned to vname.
              -a     Declares vname to be an indexed array.  If type is specified, it must be the
                     name  of  an  enumeration  type  created with the enum command and it allows
                     enumeration constants to be used as subscripts.
              -E     Declares vname to be a double precision floating point number.  If n is non-
                     zero,  it  defines  the  number  of  significant  figures that are used when
                     expanding vname.  Otherwise, ten significant figures will be used.
              -F     Declares vname to be a double precision floating point number.  If n is non-
                     zero,  it defines the number of places after the decimal point that are used
                     when expanding vname.  Otherwise ten places after the decimal point will  be
                     used.
              -H     This option provides UNIX to host-name file mapping on non-UNIX machines.
              -L     Left  justify  and  remove  leading blanks from value.  If n is non-zero, it
                     defines the width of the field, otherwise it is determined by the  width  of
                     the  value  of  first  assignment.   When the variable is assigned to, it is
                     filled on the right with blanks or truncated, if necessary, to fit into  the
                     field.  The -R option is turned off.
              -M     Use  the  character  mapping mapping defined by wctrans(3).  such as tolower
                     and toupper when assigning a value to each of the specified operands.   When
                     mapping is specified and there are not operands, all variables that use this
                     mapping are written to standard output.  When mapping is omitted  and  there
                     are no operands, all mapped variables are written to standard output.
              -R     Right  justify  and  fill with leading blanks.  If n is non-zero, it defines
                     the width of the field, otherwise it is determined by the width of the value
                     of first assignment.  The field is left filled with blanks or truncated from
                     the end if the variable is reassigned.  The -L option is turned off.
              -S     When used within the  assign_list  of  a  type  definition,  it  causes  the
                     specified  subvariable to be shared by all instances of the type.  When used
                     inside a function defined with the function  reserved  word,  the  specified
                     variables will have function static scope.  Otherwise, the variable is unset
                     prior to processing the assignment list.
              -T     If followed by tname, it creates a type named by tname  using  the  compound
                     assignment  assign_list  to  tname.   Otherwise,  it  writes  all  the  type
                     definitions to standard output.
              -X     Declares vname to be a double precision floating point  number  and  expands
                     using  the %a format of ISO-C99.  If n is non-zero, it defines the number of
                     hex digits after the radix point that is used  when  expanding  vname.   The
                     default is 10.
              -Z     Right  justify  and fill with leading zeros if the first non-blank character
                     is a digit and the -L option has not been set.  Remove leading zeros if  the
                     -L option is also set.  If n is non-zero, it defines the width of the field,
                     otherwise it is determined by the width of the value of first assignment.
              -f     The  names  refer  to  function  names  rather  than  variable  names.    No
                     assignments  can be made and the only other valid options are -S, -t, -u and
                     -x.  The -S can be used with discipline  functions  defined  in  a  type  to
                     indicate  that  the  function  is  static.   For a static function, the same
                     method will be used by all instances of that type no matter  which  instance
                     references  it.   In  addition,  it can only use value of variables from the
                     original type definition.  These discipline functions cannot be redefined in
                     any  type  instance.   The  -t  option  turns  on execution tracing for this
                     function.  The -u option causes this function to be marked  undefined.   The
                     FPATH  variable  will  be  searched to find the function definition when the
                     function is referenced.  If no options other than -f is specified, then  the
                     function  definition  will  be  displayed  on  standard  output.   If  +f is
                     specified, then a line containing the function  name  followed  by  a  shell
                     comment  containing  the  line  number  and path name of the file where this
                     function was defined, if any, is displayed.  The exit status can be used  to
                     determine  whether  the function is defined so that typeset -f .sh.math.name
                     will return 0 when math function name is defined and non-zero otherwise.
              -b     The variable can hold any number of bytes of data.  The data can be text  or
                     binary.  The value is represented by the base64 encoding of the data.  If -Z
                     is also specified, the size in bytes of the  data  in  the  buffer  will  be
                     determined  by  the  size  associated  with  the  -Z.   If the base64 string
                     assigned results in more data, it will be truncated.  Otherwise, it will  be
                     filled  with bytes whose value is zero.  The printf format %B can be used to
                     output the actual data in this buffer instead of the base64 encoding of  the
                     data.
              -g     Forces  variables  to  be created or modified at the global scope, even when
                     typeset is executed in a function defined by the function name  syntax  (see
                     Functions above) or in a name space (see Name Spaces above).
              -h     Used  within type definitions to add information when generating information
                     about the subvariable on the man page.  It is ignored when used outside of a
                     type  definition.   When used with -f the information is associated with the
                     corresponding discipline function.
              -i     Declares vname to be represented internally as integer.  The right hand side
                     of  an assignment is evaluated as an arithmetic expression when assigning to
                     an integer.  If n is  non-zero,  it  defines  the  output  arithmetic  base,
                     otherwise the output base will be ten.
              -l     Used with -i, -E or -F, to indicate long integer, or long float.  Otherwise,
                     all uppercase characters are converted to lowercase.  The uppercase  option,
                     -u, is turned off.  Equivalent to -M tolower .
              -m     Moves  or  renames  the variable.  The value is the name of a variable whose
                     value will be moved to vname.  The original variable will be unset.   Cannot
                     be used with any other options.
              -n     Declares  vname  to  be a reference to the variable whose name is defined by
                     the value of variable vname.  This is usually used to reference  a  variable
                     inside a function whose name has been passed as an argument.  Cannot be used
                     with other options except -g.
              -p     The name, attributes and values for the given vnames are written on standard
                     output  in a form that can be used as shell input.  If +p is specified, then
                     the values are not displayed.
              -r     The given vnames are marked read-only and these names cannot be  changed  by
                     subsequent assignment.
              -s     When given along with -i, restricts integer size to short.
              -t     Tags  the variables.  Tags are user definable and have no special meaning to
                     the shell.
              -u     When given along  with  -i,  specifies  unsigned  integer.   Otherwise,  all
                     lowercase  characters are converted to uppercase.  The lowercase option, -l,
                     is turned off.  Equivalent to -M toupper .
              -x     The given vnames are marked for  automatic  export  to  the  environment  of
                     subsequently-executed  commands.   Variables whose names contain a .  cannot
                     be exported.

              The -i, -F, -E, and -X options cannot be specified along with -R, -L, or  -Z.   The
              -b  option  cannot  be  specified along with -L, -u, or -l.  The -f, -m, -n, and -T
              options cannot be used together with any other option.

              Using + rather than - causes these options to be turned off.  If no vname arguments
              are  given,  a  list  of  vnames  (and  optionally  the values) of the variables is
              printed.  (Using + rather than - keeps the values  from  being  printed.)   The  -p
              option causes typeset followed by the option letters to be printed before each name
              rather than the names of the options.  If any option other than -p is  given,  only
              those  variables  which  have all of the given options are printed.  Otherwise, the
              vnames and attributes of all variables that have attributes are printed.

       ulimit [ -HSaMctdfkxlqenVuPpmrRbiswTv ] [ limit ]
              Set or display a resource limit.  The available resource limits are  listed  below.
              Many systems do not support one or more of these limits.  The limit for a specified
              resource is set when limit is specified.  The value of limit can be a number in the
              unit  specified  below  with  each resource, or the value unlimited.  The -H and -S
              options specify whether the hard limit or the soft limit for the given resource  is
              set.   A  hard  limit  cannot  be  increased  once  it is set.  A soft limit can be
              increased up to the value of the hard limit.  If neither the  H  nor  S  option  is
              specified,  the  limit applies to both.  The current resource limit is printed when
              limit is omitted.  In this case, the soft limit is printed unless H  is  specified.
              When  more  than one resource is specified, then the limit name and unit is printed
              before the value.
              -a     Lists all of the current resource limits.
              -b     The socket buffer size in bytes.
              -c     The number of 512-byte blocks on the size of core dumps.
              -d     The number of K-bytes on the size of the data area.
              -e     The scheduling priority.
              -f     The number of 512-byte blocks on files that can be written  by  the  current
                     process or by child processes (files of any size may be read).
              -i     The signal queue size.
              -k     The max number of kqueues created by the current user.
              -l     The locked address space in K-bytes.
              -M     The address space limit in K-bytes.
              -m     The number of K-bytes on the size of physical memory.
              -n     The number of file descriptors plus 1.
              -P     The max number of pseudo-terminals created by the current user.
              -p     The number of 512-byte blocks for pipe buffering.
              -q     The message queue size in K-bytes.
              -R     The  max  time a real-time process can run before blocking, in microseconds.
                     If this limit is exceeded the process is sent a SIGXCPU signal.
              -r     The max real-time priority.
              -s     The number of K-bytes on the size of the stack area.
              -T     The number of threads.
              -t     The number of CPU seconds to be used by each process.
              -u     The number of processes.
              -V     The number of open vnode monitors.
              -v     The number of K-bytes for virtual memory.
              -w     The swap size in K-bytes.
              -x     The number of file locks.

              If no option is given, -f is assumed.

       umask [ -S ] [ mask ]
              The user file-creation mask is set to mask (see umask(2)).  mask can either  be  an
              octal  number or a symbolic value as described in chmod(1).  If a symbolic value is
              given, the new umask value is the complement of the result of applying mask to  the
              complement  of  the previous umask value.  If mask is omitted, the current value of
              the mask is printed.  The -S option causes the mode to be  printed  as  a  symbolic
              value.  Otherwise, the mask is printed in octal.

       unalias [ -a ] name ...
              The  aliases  given  by  the list of names are removed from the alias list.  The -a
              option causes all the aliases to be unset.

       † unset [ -fnv ] vname ...
              The variables given by  the  list  of  vnames  are  unassigned,  i.e.,  except  for
              subvariables   within  a  type,  their  values  and  attributes  are  erased.   For
              subvariables of a type, the values are reset to the default  value  from  the  type
              definition.  Readonly variables cannot be unset.  If the -f option is set, then the
              names refer to function names.  If the -v option is set, then the  names  refer  to
              variable  names.   The  -f  option  overrides  -v.  If -n is set and name is a name
              reference, then name will be unset rather than the  variable  that  it  references.
              The  default  is  equivalent  to  -v.  Unsetting LINENO, MAILCHECK, OPTARG, OPTIND,
              RANDOM, SECONDS, TMOUT, and _ removes  their  special  meaning  even  if  they  are
              subsequently assigned to.

       wait [ job ... ]
              Wait for the specified job and report its termination status.  If job is not given,
              then all currently active child processes are waited for.   The  exit  status  from
              this  command is that of the last process waited for if job is specified; otherwise
              it is zero.  See Jobs for a description of the format of job.

       whence [ -afpPqtv ] name ...
              For each name, indicate how it would be interpreted if used as a command name.
              The -v option produces a more verbose report.  The -f option skips the  search  for
              functions.   The  -p  and  -P  options do a path search for name even if name is an
              alias, a function, or a reserved word.  Both of  these  options  turn  off  the  -v
              option.   The -q option causes whence to enter quiet mode.  whence will return zero
              if all arguments are built-ins, functions, or are programs found on the path.   The
              -t option only outputs the type of the given command.  Like -p and -P, -t will turn
              off the -v option.  The -a option is similar  to  the  -v  option  but  causes  all
              interpretations of the given name to be reported.

   Invocation.
       If  the  shell  is  invoked  by  exec(2),  initialization depends on argument zero ($0) as
       follows.  If the first character of $0 is -, or the -l option is given on  the  invocation
       command  line,  then  the  shell  is  assumed to be a login shell.  If the basename of the
       command path in $0 is rsh, rksh, or krsh, then  the  shell  becomes  restricted.   If  the
       basename  is  sh  or  rsh, or the -o posix option is given on the invocation command line,
       then the shell is initialized in full POSIX compliance mode (see the set  builtin  command
       above  for  more  information).  After this, if the shell was assumed to be a login shell,
       commands  are  read  from  /etc/profile  and  then  from  $HOME/.profile  if  it   exists.
       Alternatively,  the  option -l causes the shell to be treated as a login shell.  Next, for
       interactive shells, commands are read from the file named by ENV if the file  exists,  its
       name  being  determined  by  performing  parameter  expansion,  command  substitution, and
       arithmetic expansion on the value of that environment variable.  If the -s option  is  not
       present  and  arg  and  a  file by the name of arg exists, then it reads and executes this
       script.  Otherwise, if the first arg does not contain a /, a path search is  performed  on
       the  first  arg  to determine the name of the script to execute.  The script arg must have
       execute permission and any setuid and setgid settings will be ignored.  If the  script  is
       not  found  on  the  path, arg is processed as if it named a built-in command or function.
       Commands are then read as described below; the following options are  interpreted  by  the
       shell when it is invoked:

       -D      A  list  of  all double quoted strings that are preceded by a $ will be printed on
               standard output and the shell will exit.  This set of strings will be  subject  to
               language  translation  when  the  locale  is  not C or POSIX.  No commands will be
               executed.

       -E or -o rc or --rc
               Read the file named by the ENV variable or by $HOME/.kshrc if  not  defined  after
               the  profiles.   On  by default for interactive shells. Use +E, +o rc or --norc to
               turn off.

       -c      Read and execute a script from the first arg instead of a file.  The  second  arg,
               if  present,  becomes that script's command name ($0).  Any third and further args
               become positional parameters starting at $1.

       -s      Read and execute a script from standard input instead of a file.  The command name
               ($0)  cannot  be  set.   Any args become the positional parameters starting at $1.
               This option is forced on if no  arg  is  given  and  is  ignored  if  -c  is  also
               specified.

       -i or -o interactive or --interactive
               If  the  -i  option is present or if the shell's standard input and standard error
               are attached to  a  terminal  (as  told  by  tcgetattr(3)),  then  this  shell  is
               interactive.   In  this  case  TERM  is  ignored  (so that kill 0 does not kill an
               interactive shell) and INTR is caught and ignored (so that wait is interruptible).
               In all cases, QUIT is ignored by the shell.

       -r or -o restricted or --restricted
               If the -r option is present, the shell is a restricted shell.

       The  remaining  options  and  arguments  are  described  under  the set command above.  An
       optional - as the first argument is ignored.

   Rksh Only.
       Rksh is used to set up login names and execution environments whose capabilities are  more
       controlled  than  those of the standard shell.  The actions of rksh are identical to those
       of ksh, except that the following are disallowed:

              •      unsetting the restricted option

              •      changing directory (see cd(1))

              •      setting or unsetting the value or attributes of SHELL, ENV, FPATH, or PATH

              •      specifying path or command names containing /

              •      redirecting output (>, >|, <>, and >>)

              •      adding or deleting built-in commands

              •      using command -p to invoke a command

       The restrictions above are enforced after .profile and the ENV files are interpreted.

       When a command to be executed is found to be  a  shell  procedure,  rksh  invokes  ksh  to
       execute  it.   Thus,  it is possible to provide to the end-user shell procedures that have
       access to the full power of the standard shell, while imposing a limited menu of commands;
       this  scheme  assumes that the end-user does not have write and execute permissions in the
       same directory.

       The net effect of these rules is that the writer of the .profile has complete control over
       user  actions,  by  performing  guaranteed  setup  actions  and  leaving  the  user  in an
       appropriate directory (probably not the login directory).

       The system administrator often sets up a directory of commands (e.g., /usr/rbin) that  can
       be safely invoked by rksh.

EXIT STATUS

       Errors  detected by the shell, such as syntax errors, cause the shell to return a non-zero
       exit status.  If the shell is being used non-interactively, then execution  of  the  shell
       file  is abandoned unless the error occurs inside a subshell in which case the subshell is
       abandoned.  Otherwise, the shell returns the exit status of the last command executed (see
       also  the  exit  command  above).   Run  time errors detected by the shell are reported by
       printing the command or function name and the error condition.  If the  line  number  that
       the  error occurred on is greater than one, then the line number is also printed in square
       brackets ([]) after the command or function name.

FILES

       /etc/profile
              The system wide initialization file, executed for login shells.

       $HOME/.profile
              The personal initialization file, executed for login shells after /etc/profile.

       $HOME/.kshrc
              Default personal initialization file, executed for interactive shells when  ENV  is
              not set.

       /etc/suid_profile
              Alternative  initialization  file,  executed instead of the personal initialization
              file when the real and effective user or group ID do not match.

       /dev/null
              The null device.

SEE ALSO

       cat(1), cd(1), chmod(1), cut(1), date(1), echo(1), emacs(1),  env(1),  gmacs(1),  grep(1),
       stty(1),  test(1),  umask(1),  vi(1),  dup(2),  exec(2),  fork(2),  getpwnam(3), ioctl(2),
       lseek(2),  paste(1),  pathconf(2),  pipe(2),  sysconf(3),  umask(2),  ulimit(2),  wait(2),
       strftime(3), wctrans(3), rand(3), profile(5), environ(7).

       Morris  I.  Bolsky  and David G. Korn, The New KornShell Command and Programming Language,
       Prentice Hall, 1995.

       POSIX - Part 2: Shell and Utilities, IEEE Std 1003.2-1992, ISO/IEC 9945-2, IEEE, 1993.

CAVEATS

       If a command is executed, and then a  command  with  the  same  name  is  installed  in  a
       directory  in  the  search path before the directory where the original command was found,
       the shell will continue to exec the original command.  Use the  hash  command  or  the  -t
       option of the alias command to correct this situation.

       Using  the hist built-in command within a compound command will cause the whole command to
       disappear from the history file.

       The built-in command . file reads  the  whole  file  before  any  commands  are  executed.
       Therefore,  alias  and unalias commands in the file will not apply to any commands defined
       in the file.

       Traps are not processed while a job is waiting for a foreground process.  Thus, a trap  on
       CHLD won't be executed until the foreground job terminates.

       In  locales  that  use  a  multibyte  character  set such as UTF-8, the KEYBD trap is only
       triggered for ASCII characters (1-127).

       It is a good idea to leave a space after the comma operator in arithmetic  expressions  to
       prevent  the  comma  from  being  interpreted  as  the  decimal point character in certain
       locales.

                                                                                           KSH(1)