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NAME    [Toc]    [Back]

       ksh - Public domain Korn shell

SYNOPSIS    [Toc]    [Back]

       ksh [+-abCefhikmnprsuvxX] [+-o option] [ [ -c command-string [command-
       name] | -s | file ] [argument ...] ]

DESCRIPTION    [Toc]    [Back]

       ksh is a command interpreter that is intended for both interactive  and
       shell  script  use.   Its  command  language is a superset of the sh(1)
       shell language.

   Shell Startup    [Toc]    [Back]
       The following options can be specified only on the command line:

       -c command-string
	      the shell executes the command(s) contained in command-string

       -i     interactive mode -- see below

       -l     login shell -- see below interactive mode -- see below

       -s     the shell reads commands from  standard  input;  all  non-option
	      arguments are positional parameters

       -r     restricted mode -- see below

       In  addition  to  the  above, the options described in the set built-in
       command can also be used on the command line.

       If neither the -c nor the -s options  are  specified,  the  first  nonoption
  argument  specifies the name of a file the shell reads commands
       from; if there are no non-option arguments, the	shell  reads  commands
       from  standard input.  The name of the shell (i.e., the contents of the
       $0) parameter is determined as follows: if the -c option  is  used  and
       there is a non-option argument, it is used as the name; if commands are
       being read from a file, the file is used as  the  name;	otherwise  the
       name the shell was called with (i.e., argv[0]) is used.

       A  shell  is  interactive  if the -i option is used or if both standard
       input and standard error are attached to a tty.	An  interactive  shell
       has  job control enabled (if available), ignores the INT, QUIT and TERM
       signals, and prints prompts before  reading  input  (see  PS1  and  PS2
       parameters).   For non-interactive shells, the trackall option is on by
       default (see set command below).

       A shell is restricted if the -r option is used or if either  the  basename
 of the name the shell is invoked with or the SHELL parameter match
       the pattern *r*sh (e.g.,  rsh,  rksh,  rpdksh,  etc.).	The  following
       restrictions come into effect after the shell processes any profile and
       $ENV files:
	 o    the cd command is disabled
	 o    the SHELL, ENV and PATH parameters can't be changed
	 o    command names can't be specified with absolute or relative paths
	 o    the -p option of the command built-in can't be used
	 o    redirections  that  create files can't be used (i.e., >, >|, >>,

       A shell is privileged if the -p option is used or if the  real  user-id
       or  group-id  does  not	match  the  effective user-id or group-id (see
       getuid(2), getgid(2)).  A privileged shell does not process $HOME/.profile
 nor the ENV parameter (see below), instead the file /etc/suid_profile
 is processed.  Clearing the privileged option causes the shell  to
       set its effective user-id (group-id) to its real user-id (group-id).

       If  the	basename  of the name the shell is called with (i.e., argv[0])
       starts with - or if the -l option is used, the shell is assumed to be a
       login  shell and the shell reads and executes the contents of /etc/pro-
       file and $HOME/.profile if they exist and are readable.

       If the ENV parameter is set when the shell starts (or, in the  case  of
       login shells, after any profiles are processed), its value is subjected
       to parameter,  command,	arithmetic  and  tilde	substitution  and  the
       resulting  file (if any) is read and executed.  If ENV parameter is not
       set (and not null) and pdksh was compiled with  the  DEFAULT_ENV  macro
       defined, the file named in that macro is included (after the above mentioned
 substitutions have been performed).

       The exit status of the shell is 127 if the command  file  specified  on
       the  command  line  could  not be opened, or non-zero if a fatal syntax
       error occurred during the execution of a script.   In  the  absence  of
       fatal  errors, the exit status is that of the last command executed, or
       zero, if no command is executed.

   Command Syntax    [Toc]    [Back]
       The shell begins parsing its input by breaking it into  words.	Words,
       which  are  sequences  of  characters, are delimited by unquoted white-
       space characters (space, tab and newline) or meta-characters (<, >,  |,
       ;,  &,  (  and  )).   Aside  from delimiting words, spaces and tabs are
       ignored, while newlines usually delimit commands.  The  meta-characters
       are  used  in building the following tokens: <, <&, <<, >, >&, >>, etc.
       are used to specify redirections (see Input/Output Redirection  below);
       |  is  used to create pipelines; |& is used to create co-processes (see
       Co-Processes below); ; is used to separate commands; & is used to  create
  asynchronous  pipelines; && and || are used to specify conditional
       execution; ;; is used in case statements; (( .. )) are used  in	arithmetic
 expressions; and lastly, ( .. ) are used to create subshells.

       White-space  and meta-characters can be quoted individually using backslash
 (\), or in groups using double (") or single  (')	quotes.   Note
       that  the  following characters are also treated specially by the shell
       and must be quoted if they are to represent themselves: \, ", ', #,  $,
       `,  ~,  {,  }, *, ? and [.  The first three of these are the above mentioned
 quoting characters (see Quoting below); #, if used at the beginning
  of  a  word, introduces a comment -- everything after the # up to
       the nearest newline is ignored; $ is used to introduce parameter,  command
  and  arithmetic  substitutions (see Substitution below); ` introduces
 an old-style command substitution	(see  Substitution  below);  ~
       begins  a  directory  expansion	(see  Tilde  Expansion below); { and }
       delimit csh(1) style alternations (see  Brace  Expansion  below);  and,
       finally,  *,  ?	and  [ are used in file name generation (see File Name
       Patterns below).

       As words and tokens are parsed, the shell  builds  commands,  of  which
       there are two basic types: simple-commands, typically programs that are
       executed, and compound-commands, such as for and if statements,	grouping
 constructs and function definitions.

       A  simple-command consists of some combination of parameter assignments
       (see Parameters below),	input/output  redirections  (see  Input/Output
       Redirections  below),  and  command words; the only restriction is that
       parameter assignments come  before  any	command  words.   The  command
       words,  if any, define the command that is to be executed and its arguments.
  The command may be a shell built-in command, a function	or  an
       external  command,  i.e.,  a  separate  executable file that is located
       using the PATH parameter (see Command Execution below).	Note that  all
       command	constructs have an exit status: for external commands, this is
       related to the status returned by wait(2) (if the command could not  be
       found,  the  exit  status is 127, if it could not be executed, the exit
       status is 126); the exit status of other command  constructs  (built-in
       commands, functions, compound-commands, pipelines, lists, etc.) are all
       well defined and are described where the construct is  described.   The
       exit  status  of  a command consisting only of parameter assignments is
       that of the last command substitution performed	during	the  parameter
       assignment or zero if there were no command substitutions.

       Commands  can  be chained together using the | token to form pipelines,
       in which the standard output of each command but the last is piped (see
       pipe(2)) to the standard input of the following command.  The exit status
 of a pipeline is that of its last command.  A pipeline may be  prefixed
  by the ! reserved word which causes the exit status of the pipeline
 to be logically complemented: if the original  status  was	0  the
       complemented  status  will  be 1, and if the original status was not 0,
       then the complemented status will be 0.

       Lists of commands can be created by separating pipelines by any of  the
       following  tokens:  &&,	||, &, |& and ;.  The first two are for conditional
 execution: cmd1 && cmd2 executes cmd2 only if the exit status of
       cmd1  is  zero; || is the opposite -- cmd2 is executed only if the exit
       status of cmd1 is non-zero.  && and || have equal precedence  which  is
       higher than that of &, |& and ;, which also have equal precedence.  The
       & token causes the preceding command  to  be  executed  asynchronously,
       that is, the shell starts the command, but does not wait for it to complete
 (the shell does keep track of the status of asynchronous commands
       --  see	Job  Control  below).  When an asynchronous command is started
       when job control is disabled (i.e., in most scripts),  the  command  is
       started	with  signals  INT  and QUIT ignored and with input redirected
       from /dev/null (however, redirections  specified  in  the  asynchronous
       command have precedence).  The |& operator starts a co-process which is
       special kind of asynchronous process (see  Co-Processes	below).   Note
       that  a	command  must  follow the && and || operators, while a command
       need not follow &, |& and ;.  The exit status of a list is that of  the
       last  command  executed,  with the exception of asynchronous lists, for
       which the exit status is 0.

       Compound commands are created using the	following  reserved  words  --
       these  words  are  only recognized if they are unquoted and if they are
       used as the first word of a command (i.e., they can't  be  preceded  by
       parameter assignments or redirections):

			 case	else   function   then	  !
			 do	esac   if	  time	  [[
			 done	fi     in	  until   {
			 elif	for    select	  while   }
       Note: Some shells (but not this one) execute control structure commands
       in a subshell when one or more of  their  file  descriptors  are  redirected,
	so any environment changes inside them may fail.  To be portable,
 the exec  statement  should  be  used  instead  to	redirect  file
       descriptors before the control structure.

       In  the following compound command descriptions, command lists (denoted
       as list) that are followed by reserved words  must  end	with  a  semicolon,
 a newline or a (syntactically correct) reserved word.  For example,

	      { echo foo; echo bar; }
	      { echo foo; echo bar<newline>}
	      { { echo foo; echo bar; } }
       are all valid, but
	      { echo foo; echo bar }
       is not.

       ( list )
	      Execute list in a subshell.  There is no implicit  way  to  pass
	      environment changes from a subshell back to its parent.

       { list }
	      Compound	construct;  list  is  executed, but not in a subshell.
	      Note that { and } are reserved words, not meta-characters.

       case word in [ [(] pattern [| pattern] ... ) list ;; ] ... esac
	      The case statement attempts to match word against the  specified
	      patterns;  the  list  associated	with  the  first  successfully
	      matched pattern is executed.  Patterns used in  case  statements
	      are  the	same  as those used for file name patterns except that
	      the restrictions regarding . and / are dropped.  Note  that  any
	      unquoted space before and after a pattern is stripped; any space
	      with a pattern must be quoted.  Both the word and  the  patterns
	      are  subject  to parameter, command, and arithmetic substitution
	      as well as tilde substitution.  For historical reasons, open and
	      close braces may be used instead of in and esac (e.g., case $foo
	      { *) echo bar; }).  The exit status of a case statement is  that
	      of the executed list; if no list is executed, the exit status is

       for name [ in word ... term ] do list done
	      where term is either a newline or a ;.  For  each  word  in  the
	      specified  word  list, the parameter name is set to the word and
	      list is executed.  If in is not used to specify a word list, the
	      positional  parameters ("$1", "$2", etc.) are used instead.  For
	      historical reasons, open and close braces may be used instead of
	      do  and  done (e.g., for i; { echo $i; }).  The exit status of a
	      for statement is the last exit status of list; if list is  never
	      executed, the exit status is zero.

       if list then list [elif list then list] ... [else list] fi
	      If the exit status of the first list is zero, the second list is
	      executed; otherwise the list following the elif, if any, is executed
 with similar consequences.	If all the lists following the
	      if and elifs fail (i.e., exit with non-zero  status),  the  list
	      following the else is executed.  The exit status of an if statement
 is that of non-conditional list that  is  executed;	if  no
	      non-conditional list is executed, the exit status is zero.

       select name [ in word ... term ] do list done
	      where  term  is  either  a newline or a ;.  The select statement
	      provides an automatic method of presenting the user with a  menu
	      and  selecting  from  it.   An  enumerated list of the specified
	      words is printed on standard error, followed by a  prompt  (PS3,
	      normally	`#?  ').  A number corresponding to one of the enumerated
 words is then read from standard input, name is set to  the
	      selected word (or is unset if the selection is not valid), REPLY
	      is set to what was read (leading/trailing  space	is  stripped),
	      and  list  is executed.  If a blank line (i.e., zero or more IFS
	      characters) is entered, the menu is re-printed without executing
	      list.   When  list  completes, the enumerated list is printed if
	      REPLY is null, the prompt is printed and so on.  This process is
	      continues until an end-of-file is read, an interrupt is received
	      or a break statement is executed inside the loop.   If  in  word
	      ...  is omitted, the positional parameters are used (i.e., "$1",
	      "$2", etc.).  For historical reasons, open and close braces  may
	      be  used	instead of do and done (e.g., select i; { echo $i; }).
	      The exit status of a select statement is zero if a break	statement
 is used to exit the loop, non-zero otherwise.

       until list do list done
	      This  works  like  while,  except that the body is executed only
	      while the exit status of the first list is non-zero.

       while list do list done
	      A while is a prechecked loop.  Its body is executed as often  as
	      the exit status of the first list is zero.  The exit status of a
	      while statement is the last exit status of the list in the  body
	      of  the  loop;  if  the body is not executed, the exit status is

       function name { list }
	      Defines the function name.   See	Functions  below.   Note  that
	      redirections specified after a function definition are performed
	      whenever the function is executed, not when the function definition
 is executed.

       name () command
	      Mostly the same as function.  See Functions below.

       time [ -p ] [ pipeline ]
	      The  time  reserved  word  is described in the Command Execution

       (( expression ))
	      The arithmetic expression expression is evaluated; equivalent to
	      let  "expression".   See Arithmetic Expressions and the let command

       [[ expression ]]
	      Similar to the test and [ ... ] commands (described later), with
	      the following exceptions:
		o    Field  splitting  and  file  name generation are not performed
 on arguments.
		o    The -a (and) and -o (or) operators are replaced  with  &&
		     and ||, respectively.
		o    Operators (e.g., -f, =, !, etc.) must be unquoted.
		o    The  second  operand of != and = expressions are patterns
		     (e.g., the comparison in
					[[ foobar = f*r ]]
		o    There are two additional binary operators: < and >  which
		     return  true  if their first string operand is less than,
		     or greater than, their  second  string  operand,  respectively.

		o    The  single  argument  form  of  test, which tests if the
		     argument has non-zero length, is  not  valid  -  explicit
		     operators must be always be used, e.g., instead of
					      [ str ]
					   [[ -n str ]]
		o    Parameter,  command and arithmetic substitutions are performed
 as expressions are evaluated and  lazy  expression
		     evaluation  is  used  for	the && and || operators.  This
		     means that in the statement
				  [[ -r foo && $(< foo) = b*r ]]
		     the $(< foo) is evaluated if and only  if	the  file  foo
		     exists and is readable.

   Quoting    [Toc]    [Back]
       Quoting	is used to prevent the shell from treating characters or words
       specially.  There are three methods of quoting:	First,	\  quotes  the
       following  character,  unless it is at the end of a line, in which case
       both the \ and the newline are stripped.  Second, a  single  quote  (')
       quotes  everything  up  to the next single quote (this may span lines).
       Third, a double quote (") quotes all characters, except $, ` and \,  up
       to  the	next unquoted double quote.  $ and ` inside double quotes have
       their usual meaning (i.e., parameter, command or  arithmetic  substitution)
  except  no field splitting is carried out on the results of double-quoted
 substitutions.  If a \ inside a double-quoted string is followed
 by \, $, ` or ", it is replaced by the second character; if it is
       followed by a newline, both the \ and the newline are stripped;	otherwise,
 both the \ and the character following are unchanged.

       Note:  see  POSIX  Mode below for a special rule regarding sequences of
       the form "...`...\"...`..".

   Aliases    [Toc]    [Back]
       There are two types of aliases:	normal	command  aliases  and  tracked
       aliases.   Command aliases are normally used as a short hand for a long
       or often used command.  The shell expands command aliases  (i.e.,  substitutes
  the alias name for its value) when it reads the first word of
       a command.  An  expanded  alias	is  re-processed  to  check  for  more
       aliases.  If a command alias ends in a space or tab, the following word
       is also checked for alias expansion.  The alias expansion process stops
       when  a word that is not an alias is found, when a quoted word is found
       or when an alias word that is currently being expanded is found.

       The following command aliases are defined automatically by the shell:
	      autoload='typeset -fu'
	      functions='typeset -f'
	      hash='alias -t'
	      history='fc -l'
	      integer='typeset -i'
	      login='exec login'
	      newgrp='exec newgrp'
	      nohup='nohup '
	      r='fc -e -'
	      stop='kill -STOP'
	      suspend='kill -STOP $$'
	      type='whence -v'

       Tracked aliases allow the shell to remember where it found a particular
       command.   The  first  time  the shell does a path search for a command
       that is marked as a tracked alias, it saves the full path of  the  command.
   The  next  time	the  command is executed, the shell checks the
       saved path to see that it is still valid, and if so,  avoids  repeating
       the path search.  Tracked aliases can be listed and created using alias
       -t.  Note that changing the PATH parameter clears the saved  paths  for
       all  tracked  aliases.	If  the  trackall  option is set (i.e., set -o
       trackall or set -h), the shell tracks all commands.  This option is set
       automatically for non-interactive shells.  For interactive shells, only
       the following commands are automatically tracked: cat, cc,  chmod,  cp,
       date, ed, emacs, grep, ls, mail, make, mv, pr, rm, sed, sh, vi and who.

   Substitution    [Toc]    [Back]
       The first step the shell takes in executing a simple-command is to perform
  substitutions on the words of the command.  There are three kinds
       of substitution: parameter, command and arithmetic.  Parameter  substitutions,
  which	are  described in detail in the next section, take the
       form $name or ${...}; command substitutions take the form $(command) or
       `command`;  and arithmetic substitutions take the form $((expression)).

       If a substitution appears outside of double quotes, the results of  the
       substitution are generally subject to word or field splitting according
       to the current value of the IFS parameter.  The IFS parameter specifies
       a  list	of characters which are used to break a string up into several
       words; any characters from the set space, tab and newline  that	appear
       in  the IFS characters are called IFS white space.  Sequences of one or
       more IFS white space characters, in combination with zero or  one  nonIFS
 white space characters delimit a field.  As a special case, leading
       and trailing IFS white space is stripped (i.e., no leading or  trailing
       empty  field is created by it); leading or trailing non-IFS white space
       does create an empty field.  Example: if IFS is set to `<space>:',  the
       sequence  of  characters  `<space>A<space>:<space><space>B::D' contains
       four fields: `A', `B', `' and `D'.  Note that if the IFS  parameter  is
       set to the null string, no field splitting is done; if the parameter is
       unset, the default value of space, tab and newline is used.

       The results of substitution are, unless otherwise specified, also  subject
  to brace expansion and file name expansion (see the relevant sections

       A command substitution is replaced by the output generated by the specified
  command,	which  is run in a subshell.  For $(command) substitutions,
 normal quoting rules are used when command is  parsed,  however,
       for the `command` form, a \ followed by any of $, ` or \ is stripped (a
       \ followed by any other character is unchanged).  As a special case  in
       command	substitutions,	a command of the form < file is interpreted to
       mean substitute the contents of file ($(< foo) has the same  effect  as
       $(cat  foo),  but it is carried out more efficiently because no process
       is started).
       NOTE: $(command) expressions are currently parsed by finding the matching
  parenthesis,  regardless of quoting.  This will hopefully be fixed

       Arithmetic substitutions are replaced by the  value  of	the  specified
       expression.   For  example, the command echo $((2+3*4)) prints 14.  See
       Arithmetic Expressions for a description of an expression.

   Parameters    [Toc]    [Back]
       Parameters are shell variables; they can be assigned values  and  their
       values  can  be	accessed  using a parameter substitution.  A parameter
       name is either one of the special single punctuation or digit character
       parameters  described  below, or a letter followed by zero or more letters
 or digits (`_' counts as a letter).  The later form can be treated
       as arrays by appending an array index of the form: [expr] where expr is
       an arithmetic expression.  Array indicies are currently limited to  the
       range 0 through 1023, inclusive.  Parameter substitutions take the form
       $name, ${name} or ${name[expr]}, where name is a  parameter  name.   If
       substitution  is  performed  on a parameter (or an array parameter element)
 that is not set, a null string is substituted unless the  nounset
       option  (set  -o  nounset  or  set  -u)	is set, in which case an error

       Parameters can be assigned values in a  number  of  ways.   First,  the
       shell  implicitly  sets	some parameters like #, PWD, etc.; this is the
       only way the special single  character  parameters  are	set.   Second,
       parameters  are	imported  from	the  shell's  environment  at startup.
       Third, parameters can be assigned values on the command line, for example,
  `FOO=bar'	sets  the  parameter  FOO  to  bar; multiple parameter
       assignments can be given on a single command line and they can be  followed
  by a simple-command, in which case the assignments are in effect
       only for the  duration  of  the	command  (such	assignments  are  also
       exported,  see  below  for  implications  of this).  Note that both the
       parameter name and the = must be unquoted for the shell to recognize  a
       parameter  assignment.	The  fourth way of setting a parameter is with
       the export, readonly and typeset commands; see  their  descriptions  in
       the Command Execution section.  Fifth, for and select loops set parameters
 as well as the getopts, read and set -A commands.  Lastly, parameters
  can  be  assigned values using assignment operators inside arithmetic
 expressions (see  Arithmetic  Expressions	below)	or  using  the
       ${name=value} form of parameter substitution (see below).

       Parameters  with  the export attribute (set using the export or typeset
       -x commands, or by parameter assignments followed by  simple  commands)
       are  put  in  the  environment  (see environ(5)) of commands run by the
       shell as name=value pairs.  The order in which parameters appear in the
       environment  of a command is unspecified.  When the shell starts up, it
       extracts parameters and their values from its environment and automatically
 sets the export attribute for those parameters.

       Modifiers can be applied to the ${name} form of parameter substitution:

	      if name is set and not null, it is substituted,  otherwise  word
	      is substituted.

	      if  name	is  set  and  not null, word is substituted, otherwise
	      nothing is substituted.

	      if name is set and not null, it is substituted, otherwise it  is
	      assigned word and the resulting value of name is substituted.

	      if  name	is set and not null, it is substituted, otherwise word
	      is printed on standard error (preceded by name:)	and  an  error
	      occurs (normally causing termination of a shell script, function
	      or .-script).  If word is omitted the string `parameter null  or
	      not set' is used instead.

       In  the above modifiers, the : can be omitted, in which case the conditions
 only depend on name being set (as opposed to set and  not	null).
       If  word  is needed, parameter, command, arithmetic and tilde substitution
 are performed on it; if word is not needed, it is not evaluated.

       The following forms of parameter substitution can also be used:

	      The number of positional parameters if name is *, @  or  is  not
	      specified,  or the length of the string value of parameter name.

       ${#name[*]}, ${#name[@]}
	      The number of elements in the array name.

       ${name#pattern}, ${name##pattern}
	      If pattern matches the beginning of the value of parameter name,
	      the  matched text is deleted from the result of substitution.  A
	      single # results in the shortest match, two #'s results  in  the
	      longest match.

       ${name%pattern}, ${name%%pattern}
	      Like  ${..#..}  substitution, but it deletes from the end of the

       The following special parameters are implicitly set by  the  shell  and
       cannot be set directly using assignments:

       !      Process  id of the last background process started.  If no background
 processes have been started, the parameter is not set.

       #      The number of positional parameters (i.e., $1, $2, etc.).

       $      The process ID of the shell, or the PID of the original shell if
	      it is a subshell.

       -      The  concatenation of the current single letter options (see set
	      command below for list of options).

       ?      The exit status of the last non-asynchronous  command  executed.
	      If  the  last  command  was killed by a signal, $? is set to 128
	      plus the signal number.

       0      The name the shell was invoked with (i.e., argv[0]), or the com-
	      mand-name  if it was invoked with the -c option and the command-
	      name was supplied, or the file argument, if it was supplied.  If
	      the posix option is not set, $0 is the name of the current function
 or script.

       1 ... 9
	      The first nine positional parameters that were supplied  to  the
	      shell,  function or .-script.  Further positional parameters may
	      be accessed using ${number}.

       *      All positional parameters (except  parameter  0),  i.e.,	$1  $2
	      $3....   If  used outside of double quotes, parameters are separate
 words (which are subjected  to  word  splitting);  if  used
	      within  double  quotes,  parameters  are	separated by the first
	      character of the IFS parameter (or the empty string  if  IFS  is

       @      Same  as	$*,  unless  it is used inside double quotes, in which
	      case a separate word is generated for each positional  parameter
	      -  if  there  are no positional parameters, no word is generated
	      ("$@" can be used to access arguments, verbatim, without loosing
	      null arguments or splitting arguments with spaces).

       The following parameters are set and/or used by the shell:

       _ (underscore)
	      When  an external command is executed by the shell, this parameter
 is set in the environment of the new process to the path  of
	      the  executed  command.	In  interactive use, this parameter is
	      also set in the parent shell to the last word  of  the  previous
	      command.	 When  MAILPATH messages are evaluated, this parameter
	      contains the name of the file that changed (see MAILPATH parameter

       CDPATH Search  path for the cd built-in command.  Works the same way as
	      PATH for those directories not beginning with / in cd  commands.
	      Note  that  if CDPATH is set and does not contain . nor an empty
	      path, the current directory is not searched.

       COLUMNS    [Toc]    [Back]
	      Set to the number of columns on the terminal  or	window.   Currently
  set  to  the  cols  value as reported by stty(1) if that
	      value is non-zero.  This parameter is used  by  the  interactive
	      line  editing  modes, and by select, set -o and kill -l commands
	      to format information in columns.

       EDITOR If the VISUAL parameter is not set, this parameter controls  the
	      command  line  editing  mode for interactive shells.  See VISUAL
	      parameter below for how this works.

       ENV    If this parameter is found to be set after any profile files are
	      executed,  the  expanded value is used as a shell start-up file.
	      It typically contains function and alias definitions.

       ERRNO  Integer value of the shell's errno  variable  --	indicates  the
	      reason the last system call failed.

	      Not implemented yet.

       EXECSHELL    [Toc]    [Back]
	      If  set,	this parameter is assumed to contain the shell that is
	      to be used to execute commands that execve(2) fails  to  execute
	      and which do not start with a `#! shell' sequence.

       FCEDIT The editor used by the fc command (see below).

       FPATH  Like  PATH,  but	used when an undefined function is executed to
	      locate the file defining the function.  It is also searched when
	      a  command  can't  be found using PATH.  See Functions below for
	      more information.

       HISTFILE    [Toc]    [Back]
	      The name of the file used to store history.  When  assigned  to,
	      history  is loaded from the specified file.  Also, several invocations
 of the shell running on the same machine will share history
 if their HISTFILE parameters all point at the same file.
	      NOTE:  if  HISTFILE isn't set, no history file is used.  This is
	      different   from	 the   original   Korn	 shell,   which   uses
	      $HOME/.sh_history;  in future, pdksh may also use a default history

       HISTSIZE    [Toc]    [Back]
	      The number of commands normally stored for history, default 128.

       HOME   The  default  directory for the cd command and the value substituted
 for an unqualified ~ (see Tilde Expansion below).

       IFS    Internal field separator, used during substitution  and  by  the
	      read  command, to split values into distinct arguments; normally
	      set to space, tab  and  newline.	 See  Substitution  above  for
	      Note:  this  parameter is not imported from the environment when
	      the shell is started.

       KSH_VERSION    [Toc]    [Back]
	      The version of shell and the date the version was created (readonly).
   See also the version commands in Emacs Editing Mode and
	      Vi Editing Mode sections, below.

       LINENO The line number of the function or shell	script	that  is  currently
 being executed.

       LINES  Set to the number of lines on the terminal or window.

	      Not implemented yet.

       MAIL   If  set, the user will be informed of the arrival of mail in the
	      named file.  This parameter is ignored if the MAILPATH parameter
	      is set.

       MAILCHECK    [Toc]    [Back]
	      How  often,  in  seconds,  the  shell will check for mail in the
	      file(s) specified by MAIL or MAILPATH.  If 0, the  shell	checks
	      before each prompt.  The default is 600 (10 minutes).

       MAILPATH    [Toc]    [Back]
	      A list of files to be checked for mail.  The list is colon separated,
 and each file may be followed by a ? and a message to  be
	      printed  if new mail has arrived.  Command, parameter and arithmetic
 substitution is performed on the message, and, during substitution,
  the parameter $_ contains the name of the file.  The
	      default message is you have mail in $_.

       OLDPWD The previous working directory.  Unset if cd  has  not  successfully
  changed  directories  since  the shell started, or if the
	      shell doesn't know where it is.

       OPTARG When using getopts,  it  contains  the  argument	for  a	parsed
	      option, if it requires one.

       OPTIND The  index  of  the  last argument processed when using getopts.
	      Assigning 1 to this parameter causes getopts  to	process  arguments
 from the beginning the next time it is invoked.

       PATH   A  colon	separated  list  of directories that are searched when
	      looking for commands and .'d files.  An empty  string  resulting
	      from  a  leading	or  trailing  colon, or two adjacent colons is
	      treated as a `.', the current directory.

       POSIXLY_CORRECT    [Toc]    [Back]
	      If set, this parameter causes the posix option  to  be  enabled.
	      See POSIX Mode below.

       PPID   The process ID of the shell's parent (readonly).

       PS1    PS1  is  the  primary prompt for interactive shells.  Parameter,
	      command and arithmetic substitutions are	performed,  and  !  is
	      replaced with the current command number (see fc command below).
	      A literal ! can be put in the prompt by placing !! in PS1.  Note
	      that  since  the command line editors try to figure out how long
	      the prompt is (so they know  how	far  it  is  to  edge  of  the
	      screen), escape codes in the prompt tend to mess things up.  You
	      can tell the shell not  to  count  certain  sequences  (such  as
	      escape codes) by prefixing your prompt with a non-printing character
 (such as control-A) followed by a carriage return and then
	      delimiting  the  escape  codes with this non-printing character.
	      If you don't have any non-printing  characters,  you're  out  of
	      luck...  BTW, don't blame me for this hack; it's in the original
	      ksh.  Default is `$ ' for non-root users, `# ' for root..

       PS2    Secondary prompt string, by default `> ', used when  more  input
	      is needed to complete a command.

       PS3    Prompt  used  by select statement when reading a menu selection.
	      Default is `#? '.

       PS4    Used to prefix commands that are printed during execution  tracing
  (see  set -x command below).  Parameter, command and arithmetic
 substitutions are performed before it is printed.  Default
	      is `+ '.

       PWD    The  current  working  directory.   Maybe unset or null if shell
	      doesn't know where it is.

       RANDOM A simple random number generator.  Every time RANDOM  is	referenced,
 it is assigned the next number in a random number series.
	      The point in the series can be set by assigning a number to RAN-
	      DOM (see rand(3)).

       REPLY  Default  parameter  for  the read command if no names are given.
	      Also used in select loops to store the value that is  read  from
	      standard input.

       SECONDS    [Toc]    [Back]
	      The number of seconds since the shell started or, if the parameter
 has been assigned an integer value, the  number  of  seconds
	      since the assignment plus the value that was assigned.

       TMOUT  If  set to a positive integer in an interactive shell, it specifies
 the maximum number of seconds the shell will wait for input
	      after  printing  the  primary  prompt  (PS1).   If  the  time is
	      exceeded, the shell exits.

       TMPDIR The directory shell temporary files are  created	in.   If  this
	      parameter is not set, or does not contain the absolute path of a
	      writable directory, temporary files are created in /tmp.

       VISUAL If set, this parameter controls the command  line  editing  mode
	      for interactive shells.  If the last component of the path specified
 in this parameter contains the string vi, emacs or	gmacs,
	      the  vi, emacs or gmacs (Gosling emacs) editing mode is enabled,

   Tilde Expansion    [Toc]    [Back]
       Tilde expansion, which is done in parallel with parameter substitution,
       is done on words starting with an unquoted ~.  The characters following
       the tilde, up to the first /, if any, are assumed to be a  login  name.
       If the login name is empty, + or -, the value of the HOME, PWD, or OLD-
       PWD parameter is substituted, respectively.   Otherwise,  the  password
       file  is  searched for the login name, and the tilde expression is substituted
 with the user's home directory.  If  the  login  name  is  not
       found  in the password file or if any quoting or parameter substitution
       occurs in the login name, no substitution is performed.

       In parameter assignments (those preceding  a  simple-command  or  those
       occurring  in  the  arguments of alias, export, readonly, and typeset),
       tilde expansion is done after any unquoted colon (:), and  login  names
       are also delimited by colons.

       The  home  directory  of previously expanded login names are cached and
       re-used.  The alias -d command may be used to list, change and  add  to
       this cache (e.g., `alias -d fac=/usr/local/facilities; cd ~fac/bin').

   Brace Expansion (alternation)    [Toc]    [Back]
       Brace expressions, which take the form
       are  expanded to N words, each of which is the concatenation of prefix,
       stri and suffix (e.g., `a{c,b{X,Y},d}e'	expands  to  four  word:  ace,
       abXe,  abYe,  and ade).	As noted in the example, brace expressions can
       be nested and the resulting words are not  sorted.   Brace  expressions
       must contain an unquoted comma (,) for expansion to occur (i.e., {} and
       {foo} are not expanded).  Brace expansion is carried out after  parameter
 substitution and before file name generation.

   File Name Patterns    [Toc]    [Back]
       A  file	name  pattern is a word containing one or more unquoted ? or *
       characters or [..] sequences.  Once brace expansion has been performed,
       the  shell replaces file name patterns with the sorted names of all the
       files that match the pattern (if no  files  match,  the	word  is  left
       unchanged).  The pattern elements have the following meaning:

       ?      matches any single character.

       *      matches any sequence of characters.

       [..]   matches  any  of	the characters inside the brackets.  Ranges of
	      characters can be specified by separating two characters by a -,
	      e.g.,  [a0-9]  matches  the  letter a or any digit.  In order to
	      represent itself, a - must either be quoted or the first or last
	      character  in the character list.  Similarly, a ] must be quoted
	      or the first character in the list if  it  is  represent	itself
	      instead  of  the	end  of the list.  Also, a !  appearing at the
	      start of the list has special meaning (see below), so to	represent
 itself it must be quoted or appear later in the list.

       [!..]  like [..], except it matches any character not inside the brackets.

       *(pattern| ... |pattern)
	      matches any string of characters that matches zero or more occurances
   of   the  specified  patterns.	Example:  the  pattern
	      *(foo|bar) matches the strings `',  `foo',  `bar',  `foobarfoo',

       +(pattern| ... |pattern)
	      matches  any string of characters that matches one or more occurances
  of  the  specified  patterns.   Example:	 the   pattern
	      +(foo|bar)  matches the strings `foo', `bar', `foobarfoo', etc..

       ?(pattern| ... |pattern)
	      matches the empty string or a string that  matches  one  of  the
	      specified   patterns.   Example:	the  pattern  ?(foo|bar)  only
	      matches the strings `', `foo' and `bar'.

       @(pattern| ... |pattern)
	      matches a string that matches one  of  the  specified  patterns.
	      Example:	the  pattern @(foo|bar) only matches the strings `foo'
	      and `bar'.

       !(pattern| ... |pattern)
	      matches any string that does not match one of the specified patterns.
   Examples:  the  pattern	!(foo|bar) matches all strings
	      except `foo' and `bar'; the pattern !(*) matches no strings; the
	      pattern !(?)* matches all strings (think about it).

       Note that pdksh currently never matches . and .., but the original ksh,
       Bourne sh and bash do, so this may have to change (too bad).

       Note that none of the above pattern elements match either a period  (.)
       at the start of a file name or a slash (/), even if they are explicitly
       used in a [..] sequence; also, the names . and ..  are  never  matched,
       even by the pattern .*.

       If  the	markdirs  option is set, any directories that result from file
       name generation are marked with a trailing /.

       The POSIX character classes (i.e., [:class-name:] inside a [..] expression)
 are not yet implemented.

   Input/Output Redirection
       When  a	command  is  executed, its standard input, standard output and
       standard error (file descriptors 0, 1 and 2, respectively) are normally
       inherited  from	the  shell.   Three exceptions to this are commands in
       pipelines, for which standard input and/or standard  output  are  those
       set  up by the pipeline, asynchronous commands created when job control
       is disabled, for which standard input  is  initially  set  to  be  from
       /dev/null,  and	commands  for  which any of the following redirections
       have been specified:

       > file standard output is redirected to file.  If file does not	exist,
	      it  is  created;	if  it	does  exist, is a regular file and the
	      noclobber option is set, an error occurs, otherwise the file  is
	      truncated.   Note  that  this  means the command cmd < foo > foo
	      will open foo for reading and then truncate it when it opens  it
	      for writing, before cmd gets a chance to actually read foo.

       >| file
	      same  as	>, except the file is truncated, even if the noclobber
	      option is set.

       >> file
	      same as >, except the file  an  existing	file  is  appended  to
	      instead  of being truncated.  Also, the file is opened in append
	      mode, so writes always go to the end of the file (see  open(2)).

       < file standard	input  is  redirected  from  file, which is opened for

       <> file
	      same as <, except the file is opened for reading and writing.

       << marker
	      after reading the command line containing this kind of redirection
  (called  a  here document), the shell copies lines from the
	      command source into a  temporary	file  until  a	line  matching
	      marker is read.  When the command is executed, standard input is
	      redirected from the  temporary  file.   If  marker  contains  no
	      quoted  characters,  the contents of the temporary file are processed
 as if enclosed in double quotes each time the command  is
	      executed, so parameter, command and arithmetic substitutions are
	      performed, along with backslash (\) escapes  for	$,  `,	\  and
	      \newline.   If multiple here documents are used on the same command
 line, they are saved in order.

       <<- marker
	      same as <<, except leading tabs are stripped from lines  in  the
	      here document.

       <& fd  standard input is duplicated from file descriptor fd.  fd can be
	      a single digit,  indicating  the	number	of  an	existing  file
	      descriptor, the letter p, indicating the file descriptor associated
 with the output of the current co-process, or the character
	      -, indicating standard input is to be closed.

       >& fd  same as <&, except the operation is done on standard output.

       In  any	of  the  above redirections, the file descriptor that is redirected
 (i.e., standard input or	standard  output)  can	be  explicitly
       given  by  preceding  the  redirection with a single digit.  Parameter,
       command and arithmetic substitutions, tilde substitutions and  (if  the
       shell  is  interactive)	file  name generation are all performed on the
       file, marker and fd arguments of redirections.  Note however, that  the
       results	of  any file name generation are only used if a single file is
       matched; if multiple files match, the word  with  the  unexpanded  file
       name  generation  characters  is used.  Note that in restricted shells,
       redirections which can create files cannot be used.

       For simple-commands, redirections may appear anywhere in  the  command,
       for  compound-commands  (if  statements,  etc.),  any redirections must
       appear at the end.  Redirections are processed after pipelines are created
 and in the order they are given, so
	      cat /foo/bar 2>&1 > /dev/null | cat -n
       will print an error with a line number prepended to it.

   Arithmetic Expressions    [Toc]    [Back]
       Integer arithmetic expressions can be used with the let command, inside
       $((..)) expressions, inside array  references  (e.g.,  name[expr]),  as
       numeric	arguments  to the test command, and as the value of an assignment
 to an integer parameter.

       Expression may contain alpha-numeric parameter identifiers, array  references,
 and integer constants and may be combined with the following C
       operators (listed and grouped in increasing order of precedence).

       Unary operators:
	      + - ! ~ ++ --

       Binary operators:
	      = *= /= %= += -= <<= >>= &= ^= |=
	      == !=
	      < <= >= >
	      << >>
	      + -
	      * / %

       Ternary operator:
	      ?: (precedence is immediately higher than assignment)

       Grouping operators:
	      ( )

       Integer constants may be specified with arbitrary bases using the notation
  base#number, where base is a decimal integer specifying the base,
       and number is a number in the specified base.

       The operators are evaluated as follows:

	      unary +
		     result is the argument (included for completeness).

	      unary -

	      !      logical not; the result is 1 if argument is  zero,  0  if

	      ~      arithmetic (bit-wise) not.

	      ++     increment;  must be applied to a parameter (not a literal
		     or other expression) - the parameter is incremented by 1.
		     When  used as a prefix operator, the result is the incremented
 value of the parameter, when  used	as  a  postfix
		     operator, the result is the original value of the parameter.

	      ++     similar to ++, except the paramter is decremented by 1.

	      ,      separates two arithmetic expressions; the left hand  side
		     is  evaluated first, then the right.  The result is value
		     of the expression on the right hand side.

	      =      assignment; variable on the left is set to the  value  on
		     the right.

	      *= /= %= += -= <<= >>= &= ^= |=
		     assignment  operators;  <var> <op>= <expr> is the same as
		     <var> = <var> <op> ( <expr> ).

	      ||     logical or; the result is 1 if either  argument  is  nonzero,
  0 if not.  The right argument is evaluated only if
		     the left argument is zero.

	      &&     logical and; the result is 1 if both arguments  are  nonzero,
  0 if not.  The right argument is evaluated only if
		     the left argument is non-zero.

	      |      arithmetic (bit-wise) or.

	      ^      arithmetic (bit-wise) exclusive-or.

	      &      arithmetic (bit-wise) and.

	      ==     equal; the result is 1 if both arguments are equal, 0  if

	      !=     not equal; the result is 0 if both arguments are equal, 1
		     if not.

	      <      less than; the result is 1 if the left argument  is  less
		     than the right, 0 if not.

	      <= >= >
		     less  than or equal, greater than or equal, greater than.
		     See <.

	      << >>  shift left (right); the result is the left argument  with
		     its  bits shifted left (right) by the amount given in the
		     right argument.

	      + - * /
		     addition, subtraction, multiplication, and division.

	      %      remainder; the result is the remainder of the division of
		     the  left	argument by the right.	The sign of the result
		     is unspecified if either argument is negative.

	      <arg1> ? <arg2> : <arg3>
		     if <arg1> is non-zero, the result	is  <arg2>,  otherwise

   Co-Processes    [Toc]    [Back]
       A  co-process,  which is a pipeline created with the |& operator, is an
       asynchronous process that the shell can both write to (using print  -p)
       and  read from (using read -p).	The input and output of the co-process
       can also be manipulated using >&p and <&p  redirections,  respectively.
       Once  a co-process has been started, another can't be started until the
       co-process exits, or until the co-process  input  has  been  redirected
       using  an exec n>&p redirection.  If a co-process's input is redirected
       in this way, the next co-process to be started will  share  the	output
       with  the first co-process, unless the output of the initial co-process
       has been redirected using an exec n<&p redirection.

       Some notes concerning co-processes:
	 o    the only way to close the co-process input  (so  the  co-process
	      reads  an  end-of-file)  is  to redirect the input to a numbered
	      file descriptor and then close that file descriptor (e.g.,  exec
	      3>&p;exec 3>&-).
	 o    in  order  for  co-processes to share a common output, the shell
	      must keep the write portion of the output pipe open.  This means

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