Provided by: ksh_93u+20120801-1ubuntu0.14.04.1_amd64 bug

NAME

       ksh, ksh93 - KornShell, a command and programming language

SYNOPSIS

       ksh [ ±abcefhikmnoprstuvxBCDP ] [ -R file ] [ ±o option ] ... [ - ] [ arg ... ]
       rksh [ ±abcefhikmnoprstuvxBCD ] [ -R file ] [ ±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.  Rpfksh is a profile shell version of the command interpreter  ksh;
       it  is  used  to  to execute commands with the attributes specified by the user's profiles
       (see pfexec(1)).  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 pipe(2) to the  standard  input  of  the  next
       command.   Each command, except possibly the last, is run as a separate process; the shell
       waits for the last command to terminate.  The exit status of a pipeline is the exit status
       of  the last 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 null.  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  null  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 file-name generation
              (see File Name Generation 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.

       ((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  separate  environment.   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 sub-variables 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  sub-
                             variables  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 file name generation.  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 compiled into the shell but can be unset or redefined:
                           autoload=′typeset -fu′
                           command=′command  
                           compound=′typeset -C′
                           fc=hist
                           float=′typeset -lE′
                           functions=′typeset -f′
                           hash=′alias -t --′
                           history=′hist -l′
                           integer=′typeset -li′
                           nameref=′typeset -n′
                           nohup=′nohup  
                           r=′hist -s′
                           redirect=′command exec′
                           source=′command .′
                           stop=′kill -s STOP′
                           suspend=′kill -s STOP $$′
                           times=′{ { time;} 2>&1;}′
                           type=′whence -v′

   Tilde Substitution.
       After  alias  substitution  is performed, each word is checked to see if it begins with an
       unquoted .  For tilde substitution, word also refers to the  word  portion  of  parameter
       expansion (see Parameter Expansion below).  If it does, then the word up to a / is checked
       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.  A  followed by a + or - is replaced by the
       value of $PWD and $OLDPWD respectively.

       In addition, when expanding a variable assignment, tilde substitution  is  attempted  when
       the  value  of the assignment begins with a , and when a  appears after a :.  The : also
       terminates a  login name.

   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 Substitution.
       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  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 values and attributes to the environment.

       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 index 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 null.  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*}
              Expands to the names of the variables whose names begin with prefix.
       ${parameter:-word}
              If parameter is set and is non-null then substitute its value; otherwise substitute
              word.
       ${parameter:=word}
              If  parameter is not set or is null 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 is non-null 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 is non-null  then  substitute  word;  otherwise  substitute
              nothing.
       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 is null:
              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 associate 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 sub-pattern.  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 null, 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.

       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 decimal value returned by the last executed command.
              $      The process number of this shell.
              _      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.
              .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
                     The  value  is  set  to  ESC when processing a KEYBD trap while in vi insert
                     mode.  (See Vi Editing Mode  below.)  Otherwise,  .sh.edmode  is  null  when
                     processing a KEYBD trap.
              .sh.edtext
                     The  characters  in  the  input  buffer at the time of the most recent KEYBD
                     trap.  The value is null when not processing a KEYBD trap.
              .sh.file
                     The pathname of the file than contains the current command.
              .sh.fun
                     The name of the current function that is being executed.
              .sh.level
                     Set to the current function depth.  This can be changed inside a DEBUG  trap
                     and will set the context to the specified level.
              .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 sub-pattern 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.   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.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.
              KSH_VERSION
                     A name reference to .sh.version.
              LINENO The current line number within the script or function being executed.
              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 number of the parent of the shell.
              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 the is incremented each time the shell is invoked and is
                     exported.  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.
              COLUMNS
                     If  this  variable is set, the value is used to define the width of the edit
                     window for the shell edit modes and for printing select lists.
              EDITOR If the VISUAL variable is not set,  the  value  of  this  variable  will  be
                     checked   for   the   patterns  as  described  with  VISUAL  below  and  the
                     corresponding editing option (see Special Command set below) will be  turned
                     on.
              ENV    If this variable is set, then parameter expansion, command substitution, and
                     arithmetic substitution 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 :.
              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 "$∗" substitution
                     (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, this character is treated as if it were not in the
                     isspace class, so that if IFS consists  of  two  tab  characters,  then  two
                     adjacent tab characters delimit a null 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 staring 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
                     File Name Generation below).
              LC_NUMERIC
                     This  variable  determines  the  locale  category  for  the  decimal   point
                     character.
              LINES  If  this  variable  is set, the value is used to determine the column length
                     for printing select lists.  Select lists will print vertically  until  about
                     two-thirds of LINES lines are filled.
              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
                     substitution  with  the variable $_ defined as the name of the file that has
                     changed.  The default message is you have mail in $_.
              PATH   The search path for commands (see Execution below).  The user may not change
                     PATH if executing under rksh (except in .profile).
              PS1    The  value  of  this  variable  is expanded for parameter expansion, command
                     substitution, and arithmetic  substitution  to  define  the  primary  prompt
                     string  which  by  default is ``$''.  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.
              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  substitution  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.   If it is pfsh or pfksh, then the shell becomes a profile shell
                     (see pfexec(1)).
              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.

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

              TMOUT  If set to a value greater than zero, TMOUT will be the default timeout value
                     for the read built-in command.  The select compound command terminates after
                     TMOUT seconds when input is from a  terminal.   Otherwise,  the  shell  will
                     terminate  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 If  the  value  of this variable matches the pattern *[Vv][Ii]*, then the vi
                     option (see Special Command set below) is turned on.  If the  value  matches
                     the  pattern  *gmacs* , the gmacs option is turned on.  If the value matches
                     the pattern *macs*, then the emacs option will be turned on.  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, 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 null fields ("" or ′′) are retained.
       Implicit null fields (those resulting from parameters  that  have  no  values  or  command
       substitutions with no output) are removed.

       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
       thru 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 z4cx.

   File Name 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.   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.
       The  names  .   and  ..  are also ignored.  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 other
       uses of pattern matching the / and .  are not treated specially.

                    Matches any string, including the  null  string.   When  used  for  filename
                     expansion,  if  the  globstar  option is on, two adjacent 's by itself 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 sub-
       patterns:
              ?(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 sub-pattern 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 sub-pattern that can be used to match nested
       character expressions.  Each pattern-pair is a two character sequence which 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 alpha-
       numeric 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 sub-pattern 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
       n-th. sub-pattern, matches the same string as the sub-pattern itself.

       Finally a pattern can contain sub-patterns  of  the  form  ∼(options:pattern-list),  where
       either options or :pattern-list can be omitted.  Unlike the other compound patterns, these
       sub-patterns are not counted in the numbered sub-patterns.  :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 egrep(1) command.
              F      The remainder of the pattern uses fgrep(1) expression syntax.
              G      The  remainder  of the pattern uses basic regular expression syntax like the
                     grep(1) command.
              K      The remainder of the  pattern  uses  shell  pattern  syntax.   This  is  the
                     default.
              N      This is ignored.  However, when it is the first letter and is used with file
                     name generation, and no matches occur, the file pattern expands to the empty
                     string.
              X      The  remainder  of the pattern uses augmented regular expression syntax like
                     the xgrep(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      Treat the match as case insensitive.
              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 sub-pattern 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 substitution, to evaluate an
       arithmetic command, to evaluate an indexed array subscript, and to evaluate  arguments  to
       the  built-in  commands  shift  and let.  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 floating point constants Nan and Inf can be use to represent  "not
       a  number"  and  infinity  respectively.   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 sub-expression 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 exp2
       expm1 fabs fpclassify fdim finite floor fma fmax fmin fmod hypot ilogb int  isfinite  sinf
       isnan  isnormal  issubnormal  issubordered  iszero  j0  j1  jn  lgamma log log10 log2 logb
       nearbyint nextafter nexttoward pow remainder rint round scanb signbit sin  sinh  sqrt  tan
       tanh  tgamma  trunc  y0  y1  yn  In  addition, arithmetic functions can be define 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 cause 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 substitution, 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 file name generation 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 True, if string is not null.
       -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 sub-pattern 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 sub-pattern 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 substitution occur before word or digit
       is used except as noted  below.   File  name  generation  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(2).  built-in.

       >>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.

       <>;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(2).  built-in.

       <<[-]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 substitution,
                     command substitution, arithmetic substitution or  file  name  generation  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  substitution
                     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 substitution occur.

       <&digit       The  standard  input  is duplicated from file descriptor digit (see dup(2)).
                     Similarly for the standard output using >&digit.

       <&digit-      The file descriptor given by digit is moved to  standard  input.   Similarly
                     for the standard output using >&digit-.

       <&-           The standard input is closed.  Similarly for the standard output using >&-.

       <&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 > 10  will  be  selected  by  the
       shell  and  stored  in  the variable 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.

       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 preceded with a dagger).

       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 will not be unset unless it is unset
       explicitly from within this discipline function.

       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 staring 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 all the special built-in
       commands defined below that are preceded by ††.  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 sub-variables
       except  for sub-variables 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
       sub-variable  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
       sub-variables can be defined for any instance.

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

       When unset is invoked on a sub-variable 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
       sub-variables and the variable itself.

       A  type  definition can be derived from another type definition by defining the first sub-
       variable 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 is 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 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 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 /bin:/usr/bin: (specifying /bin, /usr/bin, and the  current  directory
       in that order).  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 after  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  sub-shell  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.

   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 ending in either of these option names.

       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.

   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  is
       null  otherwise.   By prepending ${.sh.editmode} to a value assigned to .sh.edchar it 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.

       ^F        Move cursor forward (right) one character.
       M-[C      Move cursor forward (right) one character.
       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.)
       ^B        Move cursor backward (left) one character.
       M-[D      Move cursor backward (left) one character.
       M-b       Move cursor backward one word.
       ^A        Move cursor to start of line.
       M-[H      Move cursor to start of line.
       ^E        Move cursor to end of line.
       M-[Y      Move cursor to end of line.
       ^]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  or
                 #.)  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-d       Delete current word.
       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 ^G  or  @.)
                 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).
       ^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 null.
       ^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      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      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.
       ^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 and M-^H.
       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 file name generation 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.
       \         Escape next character.  Editing characters, the user's erase, kill and interrupt
                 (normally ^?)  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).
       M-^V      Display version of the shell.
       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.

       When in vi mode on most systems, canonical processing is initially enabled and the command
       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  option  viraw  is  also  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.

        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.
              \         Escape 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 Cursor forward (right) one character.
              [count]w  Cursor forward one alpha-numeric 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 Cursor backward (left) one character.
              [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.
              ^         Cursor to start of line.
              [H        Cursor to first non-blank character in line.
              $         Cursor to end of line.
              [Y        Cursor to end of line.
              %         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 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 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 null,  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 beginning of the line.  Equivalent to 0i.
              [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]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 file  name  generation
                        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 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 following simple-commands are executed in the shell process.  Input/Output redirection
       is  permitted.  Unless otherwise indicated, the output is written on file descriptor 1 and
       the exit status, when there is no syntax error, is zero.  Except for :, true, false, echo,
       newgrp,  and login, all built-in commands accept -- to indicate end of options.  They also
       interpret the option --man as a request to display the man page onto standard error and -?
       as  a  help  request  which  prints  a usage message on standard error.  Commands that are
       preceded by one or two † symbols 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.
       5.     Words following a command preceded by †† that are  in  the  format  of  a  variable
              assignment  are  expanded with the same rules as a variable assignment.  This means
              that tilde substitution is performed after the = sign and field splitting and  file
              name generation are not performed.  These are called declaration built-ins.

       † : [ 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.

       †† 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.   The  obsolete  -t  option  is  used  to set and list tracked
              aliases.  The value of a tracked alias is the full pathname  corresponding  to  the
              given  name.   The  value becomes undefined when the value of PATH is reset but the
              alias remains tracked.  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.  The exit status is non-zero if a name is  given,
              but no value, and no alias has been defined for the name.

       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 be 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 [ -LP ] [ arg ]
       cd [ -LP ] 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 <null> (specifying the current directory).  Note that the
              current  directory  is  specified by a null path name, 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.
              The cd command may not be executed by rksh.  rksh93.

       command [ -pvxV ] name [ arg ... ]
              Without the -v or -V options, command executes name with  the  arguments  given  by
              arg.   The  -p  option  causes  a  default  path to be searched rather than the one
              defined by the value of PATH.  Functions will not  be  searched  for  when  finding
              name.   In  addition,  if  name  refers  to a special built-in, none of the special
              properties associated with the leading daggers will be honored.  (For example,  the
              predefined alias redirect=′command exec′ prevents a script from terminating when an
              invalid redirection is given.)  With the -x  option,  if  command  execution  would
              result  in  a  failure because there are too many arguments, errno E2BIG, the shell
              will invoke command name multiple times with a subset  of  the  arguments  on  each
              invocation.   Arguments that occur prior to the first word that expands to multiple
              arguments and after the last word that expands to multiple arguments will be passed
              on  each  invocation.   The exit status will be the maximum invocation exit status.
              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.

       † 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 a declaration command named type that is an integer type that allows one of
              the  specified  values as enumeration names.  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.

       † 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 -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.  Input/output arguments may  appear  and  affect  the  current
              process.   If  arg  is  not  given,  the  effect  of this command is to modify file
              descriptors as prescribed by the input/output redirection list.  In this case,  any
              file  descriptor  numbers  greater  than  2 that are opened with this mechanism are
              closed when invoking another program.

       † exit [ n ]
              Causes the shell to exit with the exit status specified by n.  The  value  will  be
              the  least  significant  8 bits of the specified status.  If n is omitted, then the
              exit status is that of the last command executed.  An end-of-file will  also  cause
              the shell to exit except for a shell which has the ignoreeof option (see set below)
              turned on.

       †† 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.

       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.

       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(2).)  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.

       hist [ -e ename  ] [ -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.

       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 list only the
              signal names.   -L  options  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 constants 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.

       † newgrp [ arg ... ]
              Equivalent to exec /bin/newgrp arg ....

       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 new-line 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 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 can be used instead of %s to cause arg to be interpreted as an
                     extended regular expression and be printed as a shell pattern.
              %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.
              %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 use to treat  an  argument  as  a  date/time
                     string  and  to format the date/time according to the date-format as defined
                     for the date(1) command.
              %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.)

       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  [ -ACSprsv ] [ -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  -d  option
              causes  the  read to continue to the first character of delim rather than new-line.
              The -n option causes at most n bytes to read rather a full  line  but  will  return
              when  reading  from a slow device as soon as any characters have been read.  The -N
              option causes exactly n to be read unless an end-of-file has  been  encountered  or
              the  read  times out because of the -t option.  In raw mode, -r, the \ character is
              not treated specially.  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.
              When vname has the binary attribute and -n or -N is specified, the bytes  that  are
              read are stored directly into the variable.  If the -v is specified, then the value
              of the first vname will be used as a default value when  reading  from  a  terminal
              device.  The -A option causes the variable vname to be unset and each field that is
              read to be stored in successive elements of the indexed array vname.  The -C option
              causes  the  variable  vname  to  be  read  as a compound variable.  Blanks will be
              ignored when finding the beginning open parenthesis.  The -S option 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.   The  -p  option causes the input line to be taken from the input pipe of a
              process spawned by the shell using ⎪&.  If the -s option is present, the input will
              be  saved as a command in the history file.  The option -u can be used to specify a
              one digit file descriptor unit unit to read  from.   The  file  descriptor  can  be
              opened  with  the exec special built-in command.  The default value of unit n is 0.
              The option -t is used to specify a timeout in seconds when reading from a  terminal
              or pipe.  If vname is omitted, then REPLY is used as the default vname.  An end-of-
              file with the -p option causes cleanup for this process  so  that  another  can  be
              spawned.  If the first argument contains a ?, the remainder of this word is used as
              a prompt on standard error when the shell is interactive.  The  exit  status  is  0
              unless an end-of-file is encountered or read has timed out.

       †† readonly [ -p ] [ vname[=value] ] ...
              If  vname  is  not  given,  the names and values of each variable with the readonly
              attribute is printed with the values quoted in a manner that allows them to be  re-
              inputted.   The  -p option causes the word readonly to be inserted before each one.
              Otherwise, the given vnames are marked readonly and these names cannot  be  changed
              by  subsequent  assignment.   When defining a type, if the value of a readonly sub-
              variable is not defined the value is required when creating each instance.

       † return [ n ]
              Causes a shell function or .  script to return to the invoking script with the exit
              status  specified  by  n.   The  value  will be the least significant 8 bits of the
              specified status.  If n is omitted, then the return status  is  that  of  the  last
              command  executed.   If  return  is invoked while not in a function or a .  script,
              then it behaves the same as exit.

       † set [ ±BCGabefhkmnoprstuvx ] [ ±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 pattern field generation.  This is the default behavior.
              -B      Enable brace group expansion.  On by default.
              -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      Causes the pattern ∗∗ by itself to match files and zero or more directories
                      and sub-directories when used for file name generation.  If followed by a /
                      only directories and sub-directories are matched.
              -a      All subsequent variables that are defined are automatically exported.
              -b      Prints  job  completion  messages as soon as a background job changes state
                      rather than waiting for the next prompt.
              -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 file name generation.
              -h      Each command becomes a tracked alias when first encountered.
              -k      (Obsolete). 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.  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.
                      errexit Same as -e.
                      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.
                      globstar
                              Same as -G.
                      gmacs   Puts you in a gmacs style in-line editor for command entry.
                      ignoreeof
                              The  shell  will not exit on end-of-file.  The command exit must be
                              used.
                      keyword Same as -k.
                      letoctal
                              The let command allows octal constants starting with 0.
                      markdirs
                              All directory names resulting from  file  name  generation  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   Do not save function definitions in the history file.
                      notify  Same as -b.
                      nounset Same as -u.
                      pipefail
                              A  pipeline  will not complete until all components of the pipeline
                              have completed, and the return value will be the value of the  last
                              non-zero command to fail or zero if no command has failed.
                      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.
                      privileged
                              Same as -p.
                      verbose Same as -v.
                      trackall
                              Same as -h.
                      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.
                      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.
              -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 seconds
              Suspends execution for the number of decimal seconds or fractions of a second given
              by seconds.

       † 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 null 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  contents  of  the  current  command  line when action is running.  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.

       ††  typeset  [  ±ACHSfblmnprtux  ]  [  ±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.   value  names  a  compound
                     variable it is copied into vname.  Otherwise, it unsets each 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 sub-variable 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.
              -h     Used within type definitions to add information when generating  information
                     about  the sub-variable 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  upper-case  characters  are  converted  to  lower-case.  The upper-case
                     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 any other options.
              -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 readonly and these names cannot be changed by
                     subsequent assignment.
              -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 lower-
                     case characters are converted to upper-case.  The lower-case 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 attribute cannot be specified along with -R, -L, -Z, or -f.

              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 [ -HSacdfmnpstv ] [ 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.
              -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.
              -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).
              -m     The number of K-bytes on the size of physical memory.
              -n     The number of file descriptors plus 1.
              -p     The number of 512-byte blocks for pipe buffering.
              -s     The number of K-bytes on the size of the stack area.
              -t     The number of CPU seconds to be used by each process.
              -v     The number of K-bytes for virtual memory.

              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  sub-
              variables within a type, their values and attributes are erased.  For sub-variables
              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 [ -afpv ] 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 option does a path search for name even if name is an alias, a
              function, or a reserved word.  The -p option turns  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), and the first character of argument zero  ($0)  is  -,
       then  the shell is assumed to be a login shell and commands are read from /etc/profile and
       then from either .profile in the current  directory  or  $HOME/.profile,  if  either  file
       exists.  Next, for interactive shells, commands are read from the file named by performing
       parameter expansion, command substitution, and arithmetic substitution on the value of the
       environment  variable ENV if the file exists.  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      Do not execute the script, but output the set of double quoted strings preceded by
               a  $.   These  strings  are  needed  for  localization  of the script to different
               locales.
       -E      Reads the file named by the ENV variable or by $HOME/.kshrc if not  defined  after
               the profiles.
       -c        If  the  -c  option  is present, then commands are read from the first arg.  Any
                 remaining arguments become positional parameters starting at 0.
       -s        If the -s option is present or if no arguments remain, then  commands  are  read
                 from  the  standard  input.   Shell output, except for the output of the Special
                 Commands listed above, is written to file descriptor 2.
       -i        If the -i option is present or if the shell input and output are attached  to  a
                 terminal  (as  told  by  tcgetattr(2)), 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 ).  In all cases, QUIT is ignored by
                 the shell.
       -r        If the -r option is present, the shell is a restricted shell.
       -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.

       -P        If -P or -o profile is present, the shell is a profile shell (see pfexec(1)).

       -R filename
                 The  -R  filename option is used to generate a cross reference database that can
                 be used by a separate utility to find definitions and references  for  variables
                 and commands.

       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
              NULL device

SEE ALSO

       cat(1), cd(1), chmod(1), cut(1), egrep(1), echo(1), emacs(1), env(1), fgrep(1),  gmacs(1),
       grep(1),  newgrp(1),  pfexec(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(2),
       umask(2), ulimit(2), wait(2), wctrans(3), rand(3), a.out(5), 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  -t  option  of  the  alias
       command to correct this situation.

       Some very old shell scripts contain a ^ as a synonym for the pipe character .

       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.

       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)