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SH(1)			   OpenBSD Reference Manual			 SH(1)

     sh - public domain Bourne shell

     sh [-+abCefhiklmnpruvXx] [-+o option] [-c string | -s | file
	[argument ...]]

     sh is a reimplementation of the Bourne shell, a command interpreter for
     both interactive and script use.

     The options are as follows:

     -c string
	     sh will execute the command(s) contained in string.

     -i	     Interactive shell.	 A shell is ``interactive'' if this option is
	     used or if both standard input and standard error are attached to
	     a tty(4).	An interactive shell has job control enabled, ignores
	     the SIGINT, SIGQUIT, and SIGTERM signals, and prints prompts
	     before reading input (see the PS1 and PS2 parameters).  For non-
	     interactive shells, the trackall option is on by default (see the
	     set command below).

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

     -p	     Privileged shell.	A shell is ``privileged'' if this 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) and 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

     -r	     Restricted shell.	A shell is ``restricted'' if this option is
	     used; if the basename the shell was invoked with was ``rsh''; or
	     if the SHELL parameter is set to ``rsh''.	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 cannot be changed.
	     o	 Command names can't be specified with absolute or relative
	     o	 The -p option of the built-in command command can't be used.
	     o	 Redirections that create files can't be used (i.e. `>', `>|',
		 `>>', `<>').

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

     In addition to the above, the options described in the set built-in
     command can also be used on the command line: both [-+abCefhkmnuvXx] and
     [-+o option] can be used for single letter or long options, respectively.

     If neither the -c nor the -s option is specified, the first non-option
     argument specifies the name of a file the shell reads commands from.  If
     there are no non-option arguments, the shell reads commands from the
     standard input.  The name of the shell (i.e. the contents of $0) 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 basename the shell was
     called with (i.e. argv[0]) is used.

     If the ENV parameter is set when an interactive 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.

     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
     The shell begins parsing its input by breaking it into words.  Words,
     which are sequences of characters, are delimited by unquoted whitespace
     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
     separate commands; `&' is used to create asynchronous pipelines; `&&' and
     `||' are used to specify conditional execution; `;;' is used in case
     statements; and lastly, `( .. )' is used to create subshells.

     Whitespace and meta-characters can be quoted individually using a
     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 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 0 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; if the original status was not 0, 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.  Note that the `&&' and `||' operators are
     "left-associative".  For example, both of these commands will print only

	   $ false && echo foo || echo bar
	   $ true || echo foo && echo bar

     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 SIGINT and SIGQUIT ignored and with input
     redirected from /dev/null (however, redirections specified in the
     asynchronous command have precedence).  Note that a command must follow
     the `&&' and `||' operators, while it need not follow `&', `|&', or `;'.
     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	  esac	     in	      while   ]]
	   do	  fi	     name     !	      {
	   done	  for	     select   (	      }
	   elif	  function   then     )
	   else	  if	     until    [[

     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, the
     following are all valid:

	   $ { echo foo; echo bar; }
	   $ { echo foo; echo bar<newline> }
	   $ { { echo foo; echo bar; } }

     This is not valid:

	   $ { echo foo; echo bar }

     (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 a specified
	     pattern; 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
	     within 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 ...]; do list; done
	     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 ...]; do list; done
	     The select statement provides an automatic method of presenting
	     the user with a menu and selecting from it.  An enumerated list
	     of the specified word(s) 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 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 reprinted without
	     executing list.

	     When list completes, the enumerated list is printed if REPLY is
	     NULL, the prompt is printed, and so on.  This process 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 pre-checked 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).

     [[ 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', `=', `!') must be unquoted.

		   o   The second operand of the `!=' and `=' expressions are
		       patterns (e.g. the comparison [[ 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,

		   o   The single argument form of test, which tests if the
		       argument has a non-zero length, is not valid; explicit
		       operators must always be used e.g. instead of [ str ]
		       use [[ -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 following statement,
		       $(< foo) is evaluated if and only if the file foo
		       exists and is readable:

			     $ [[ -r foo && $(< foo) = b*r ]]

     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

     Note: See POSIX mode below for a special rule regarding differences in
     quoting when the shell is in POSIX mode.

     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:

	   hash='alias -t'
	   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(1), cc(1), chmod(1), cp(1), date(1),
     ed(1), emacs(1), grep(1), ls(1), mail(1), make(1), mv(1), pr(1), rm(1),
     sed(1), vi(1), and who(1).

     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 whitespace''.	Sequences of one or
     more IFS whitespace characters, in combination with zero or one non-IFS
     whitespace characters, delimit a field.  As a special case, leading and
     trailing IFS whitespace is stripped (i.e. no leading or trailing empty
     field is created by it); leading non-IFS whitespace does create an empty

     Example: If IFS is set to ``<space>:'', and VAR is set to
     ``<space>A<space>:<space><space>B::D'', the substitution for $VAR results
     in four fields: `A', `B', `' (an empty field), 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

     Also, note that the field splitting applies only to the immediate result
     of the substitution.  Using the previous example, the substitution for
     $VAR:E results in the fields: `A', `B', `', and `D:E', not `A', `B', `',
     `D', and `E'.  This behavior is POSIX compliant, but incompatible with
     some other shell implementations which do field splitting on the word
     which contained the substitution or use IFS as a general whitespace

     The results of substitution are, unless otherwise specified, also subject
     to file name expansion (see the relevant section below).

     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.  Note that $(< 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 should be fixed soon.

     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 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).  Parameter substitutions take the
     form $name, ${name}, or ${name[expr]} where name is a parameter name.  If
     substitution is performed on a parameter 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 occurs.

     Parameters can be assigned values in a number of ways.  First, the shell
     implicitly sets some parameters like `#', `PWD', and `$'; 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 the 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 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 the
     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(7)) 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 sourced using the `.' built-in).	 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

     The following forms of parameter substitution can also be used:

	     The number of positional parameters if name is `*', `@', or not
	     specified; otherwise the length of the string value of parameter

	     The number of elements in the array name.

	     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, and two of them result
	     in the longest match.

	     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

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

     $	      The PID of the shell, or the PID of the original shell if it is
	      a subshell.  Do NOT use this mechanism for generating temporary
	      file names; see mktemp(1) instead.

     -	      The concatenation of the current single letter options (see the
	      set command below for a 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 of the shell, determined as follows: the first argument
	      to sh if it was invoked with the -c option and arguments were
	      given; otherwise the file argument, if it was supplied; or else
	      the basename the shell was invoked with (i.e. argv[0]).  $0 is
	      also set to the name of the current script or the name of the
	      current function, if it was defined with the function keyword
	      (i.e. a Korn shell style function).

     1 ... 9  The first nine positional parameters that were supplied to the
	      shell, function, or script sourced using the `.' built-in.
	      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 NULL).

     @	      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 losing NULL
	      arguments or splitting arguments with spaces.

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

     CDPATH	Search path for the cd built-in command.  It 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 `.'
		or contains an empty path, the current directory is not
		searched.  Also, the cd built-in command will display the
		resulting directory when a match is found in any search path
		other than the empty path.

     COLUMNS	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 set -o
		and kill -l commands to format information columns.

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

     ERRNO	Integer value of the shell's errno variable.  It indicates the
		reason the last system call failed.  Not yet implemented.

     EXECSHELL	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.

     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 details.

		Note: This parameter is not imported from the environment when
		the shell is started.

		The version of shell and the date the version was created

     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.

     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 next argument to be processed when using
		getopts.  Assigning 1 to this parameter causes getopts to
		process arguments from the beginning the next time it is

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

		If set, this parameter causes the posix option to be enabled.
		See POSIX mode below.

     PPID	The process ID of the shell's parent (read-only).

     PS1	The primary prompt for interactive shells.  Parameter,
		command, and arithmetic substitutions are performed.  `!' is
		replaced with the current command number (see the fc command
		below).	 A literal `!' can be put in the prompt by placing
		`!!' in PS1.  The default is `$ ' for non-root users, `# ' for

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

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

     PWD	The current working directory.	May be unset or NULL if the
		shell doesn't know where it is.

     REPLY	Default parameter for the read command if no names are given.

     TMPDIR	The directory temporary shell 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.

   Tilde expansion
     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
     OLDPWD 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 (such as those preceding a simple-command or
     those occurring in the arguments of alias, export, readonly, and
     typeset), tilde expansion is done after any assignment (i.e. after the
     equals sign) or after an unquoted colon (`:'); 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).

   File name patterns
     A file name pattern is a word containing one or more unquoted `?', `*',
     `+', `@', or `!' characters or ``[..]'' sequences.	 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 to 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.

	     Within a bracket expression, the name of a character class
	     enclosed in `[:' and `:]' stands for the list of all characters
	     belonging to that class.  Supported character classes:

		   alnum     cntrl     lower	 space
		   alpha     digit     print	 upper
		   blank     graph     punct	 xdigit

	     These match characters using the macros specified in ctype(3).  A
	     character class may not be used as an endpoint of a range.

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

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

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

	     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''.

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

	     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 `/'.

   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

     > 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 if file exists it 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 expanded 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 the following will print an error with a
     line number prepended to it:

	   $ cat /foo/bar 2>&1 > /dev/null | cat -n

   Arithmetic expressions
     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.

     Expressions 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 operators:

	   ?: (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.  Additionally,
     integers may be prefixed with `0X' or `0x' (specifying base 16) or `0'
     (base 8) in all forms of arithmetic expressions, except as numeric
     arguments to the test command.

     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 not.

	   ~	   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

	   --	   Similar to ++, except the parameter is decremented by 1.

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

	   =	   Assignment; the 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>, with any operator precedence in
		   <expr> preserved.  For example, ``var1 *= 5 + 3'' is the
		   same as specifying ``var1 = var1 * (5 + 3)''.

	   ||	   Logical OR; the result is 1 if either argument is non-zero,
		   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 non-
		   zero, 0 if not.  The right argument is evaluated only if
		   the left argument is non-zero.

	   |	   Arithmetic (bit-wise) OR.

	   ^	   Arithmetic (bit-wise) XOR (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.

		   If <arg1> is non-zero, the result is <arg2>; otherwise the
		   result is <arg3>.

     Functions are defined using either Korn shell function function-name
     syntax or the Bourne/POSIX shell function-name() syntax (see below for
     the difference between the two forms).  Functions are like .-scripts
     (i.e. scripts sourced using the `.' built-in) in that they are executed
     in the current environment.  However, unlike .-scripts, shell arguments
     (i.e. positional parameters $1, $2, etc.) are never visible inside them.
     When the shell is determining the location of a command, functions are
     searched after special built-in commands, before regular and non-regular
     built-ins, and before the PATH is searched.

     An existing function may be deleted using unset -f function-name.	A list
     of functions can be obtained using typeset +f and the function
     definitions can be listed using typeset -f.  The autoload command (which
     is an alias for typeset -fu) may be used to create undefined functions:
     when an undefined function is executed, the shell searches the path
     specified in the FPATH parameter for a file with the same name as the
     function, which, if found, is read and executed.  If after executing the
     file the named function is found to be defined, the function is executed;
     otherwise, the normal command search is continued (i.e. the shell
     searches the regular built-in command table and PATH).  Note that if a
     command is not found using PATH, an attempt is made to autoload a
     function using FPATH (this is an undocumented feature of the original
     Korn shell).

     Functions can have two attributes, ``trace'' and ``export'', which can be
     set with typeset -ft and typeset -fx, respectively.  When a traced
     function is executed, the shell's xtrace option is turned on for the
     function's duration; otherwise, the xtrace option is turned off.  The
     ``export'' attribute of functions is currently not used.  In the original
     Korn shell, exported functions are visible to shell scripts that are

     Since functions are executed in the current shell environment, parameter
     assignments made inside functions are visible after the function
     completes.	 If this is not the desired effect, the typeset command can be
     used inside a function to create a local parameter.  Note that special
     parameters (e.g. $$, $!) can't be scoped in this way.

     The exit status of a function is that of the last command executed in the
     function.	A function can be made to finish immediately using the return
     command; this may also be used to explicitly specify the exit status.

     Functions defined with the function reserved word are treated differently
     in the following ways from functions defined with the () notation:

     o	 The $0 parameter is set to the name of the function (Bourne-style
	 functions leave $0 untouched).

     o	 Parameter assignments preceding function calls are not kept in the
	 shell environment (executing Bourne-style functions will keep

     o	 OPTIND is saved/reset and restored on entry and exit from the
	 function so getopts can be used properly both inside and outside the
	 function (Bourne-style functions leave OPTIND untouched, so using
	 getopts inside a function interferes with using getopts outside the

     In the future, the following differences will also be added:

     o	 A separate trap/signal environment will be used during the execution
	 of functions.	This will mean that traps set inside a function will
	 not affect the shell's traps and signals that are not ignored in the
	 shell (but may be trapped) will have their default effect in a

     o	 The EXIT trap, if set in a function, will be executed after the
	 function returns.

   POSIX mode
     The shell is intended to be POSIX compliant; however, in some cases,
     POSIX behaviour is contrary either to the original Korn shell behaviour
     or to user convenience.  How the shell behaves in these cases is
     determined by the state of the posix option (set -o posix).  If it is on,
     the POSIX behaviour is followed; otherwise, it is not.  The posix option
     is set automatically when the shell starts up if the environment contains
     the POSIXLY_CORRECT parameter.  The shell can also be compiled so that it
     is in POSIX mode by default; however, this is usually not desirable.

     The following is a list of things that are affected by the state of the
     posix option:

     o	 Reading of $ENV: if not in posix mode, the ENV parameter is not
	 expanded and included when the shell starts.

     o	 Occurrences of \" inside double quoted `..` command substitutions.
	 In POSIX mode, the \" is interpreted when the command is interpreted;
	 in non-POSIX mode, the backslash is stripped before the command
	 substitution is interpreted.  For example, echo "`echo \"hi\"`"
	 produces ``"hi"'' in POSIX mode, ``hi'' in non-POSIX mode.  To avoid
	 problems, use the $(...) form of command substitution.

     o	 kill -l output.  In POSIX mode, only signal names are listed (in a
	 single line); in non-POSIX mode, signal numbers, names, and
	 descriptions are printed (in columns).	 In the future, a new option
	 (-v perhaps) will be added to distinguish the two behaviours.

     o	 echo options.	In POSIX mode, -e and -E are not treated as options,
	 but printed like other arguments; in non-POSIX mode, these options
	 control the interpretation of backslash sequences.

     o	 fg exit status.  In POSIX mode, the exit status is 0 if no errors
	 occur; in non-POSIX mode, the exit status is that of the last
	 foregrounded job.

     o	 getopts.  In POSIX mode, options must start with a `-'; in non-POSIX
	 mode, options can start with either `-' or `+'.

     o	 set -.	 In POSIX mode, this does not clear the verbose or xtrace
	 options; in non-POSIX mode, it does.

     o	 set exit status.  In POSIX mode, the exit status of set is 0 if there
	 are no errors; in non-POSIX mode, the exit status is that of any
	 command substitutions performed in generating the set command.	 For
	 example, set -- `false`; echo $? prints 0 in POSIX mode, 1 in non-
	 POSIX mode.  This construct is used in most shell scripts that use
	 the old getopt(1) command.

     o	 Argument expansion of the alias, export, readonly, and typeset
	 commands.  In POSIX mode, normal argument expansion is done; in non-
	 POSIX mode, field splitting, file globbing, and (normal) tilde
	 expansion are turned off, while assignment tilde expansion is turned

     o	 Signal specification.	In POSIX mode, signals can be specified as
	 digits, only if signal numbers match POSIX values (i.e. HUP=1, INT=2,
	 QUIT=3, ABRT=6, KILL=9, ALRM=14, and TERM=15); in non-POSIX mode,
	 signals can always be digits.

     o	 Alias expansion.  In POSIX mode, alias expansion is only carried out
	 when reading command words; in non-POSIX mode, alias expansion is
	 carried out on any word following an alias that ended in a space.
	 For example, the following for loop uses parameter `i' in POSIX mode
	 and `j' in non-POSIX mode:

	       alias a='for ' i='j'
	       a i in 1 2; do echo i=$i j=$j; done

     o	 test.	In POSIX mode, the expression `-t' (preceded by some number of
	 `!' arguments) is always true as it is a non-zero length string; in
	 non-POSIX mode, it tests if file descriptor 1 is a tty(4) (i.e. the
	 fd argument to the -t test may be left out and defaults to 1).

   Command execution
     After evaluation of command-line arguments, redirections, and parameter
     assignments, the type of command is determined: a special built-in, a
     function, a regular built-in, or the name of a file to execute found
     using the PATH parameter.	The checks are made in the above order.
     Special built-in commands differ from other commands in that the PATH
     parameter is not used to find them, an error during their execution can
     cause a non-interactive shell to exit, and parameter assignments that are
     specified before the command are kept after the command completes.	 Just
     to confuse things, if the posix option is turned off (see the set command
     below), some special commands are very special in that no field
     splitting, file globbing, nor tilde expansion is performed on arguments
     that look like assignments.  Regular built-in commands are different only
     in that the PATH parameter is not used to find them.

     The original ksh and POSIX differ somewhat in which commands are
     considered special or regular:

     POSIX special commands

     ., :, break, continue, eval, exec, exit, export, readonly, return, set,
     shift, trap, unset

     Additional sh special commands

     builtin, times, typeset

     Very special commands (non-POSIX)

     alias, readonly, set, typeset

     POSIX regular commands

     alias, bg, cd, command, false, fc, fg, getopts, jobs, kill, read, true,
     umask, unalias, wait

     Additional sh regular commands

     [, echo, let, print, pwd, test, ulimit, whence

     In the future, the additional sh special and regular commands may be
     treated differently from the POSIX special and regular commands.

     Once the type of command has been determined, any command-line parameter
     assignments are performed and exported for the duration of the command.

     The following describes the special and regular built-in commands:

     . file [arg ...]
	     Execute the commands in file in the current environment.  The
	     file is searched for in the directories of PATH.  If arguments
	     are given, the positional parameters may be used to access them
	     while file is being executed.  If no arguments are given, the
	     positional parameters are those of the environment the command is
	     used in.

     : [...]
	     The null command.	Exit status is set to zero.

     alias [-d | -t [-r] | +-x] [-p] [+] [name [=value] ...]
	     Without arguments, alias lists all aliases.  For any name without
	     a value, the existing alias is listed.  Any name with a value
	     defines an alias (see Aliases above).

	     When listing aliases, one of two formats is used.	Normally,
	     aliases are listed as name=value, where value is quoted.  If
	     options were preceded with `+', or a lone `+' is given on the
	     command line, only name is printed.

	     The -d option causes directory aliases, which are used in tilde
	     expansion, to be listed or set (see Tilde expansion above).

	     If the -p option is used, each alias is prefixed with the string
	     ``alias ''.

	     The -t option indicates that tracked aliases are to be listed/set
	     (values specified on the command line are ignored for tracked
	     aliases).	The -r option indicates that all tracked aliases are
	     to be reset.

	     The -x option sets (+x clears) the export attribute of an alias,
	     or, if no names are given, lists the aliases with the export
	     attribute (exporting an alias has no effect).

     bg [job ...]
	     Resume the specified stopped job(s) in the background.  If no
	     jobs are specified, %+ is assumed.	 See Job control below for
	     more information.

     break [level]
	     Exit the levelth inner-most for, until, or while loop.  level
	     defaults to 1.

     builtin command [arg ...]
	     Execute the built-in command command.

     cd [-LP] [dir]
	     Set the working directory to dir.	If the parameter CDPATH is
	     set, it lists the search path for the directory containing dir.
	     A NULL path means the current directory.  If dir is found in any
	     component of the CDPATH search path other than the NULL path, the
	     name of the new working directory will be written to standard
	     output.  If dir is missing, the home directory HOME is used.  If
	     dir is `-', the previous working directory is used (see the
	     OLDPWD parameter).

	     If the -L option (logical path) is used or if the physical option
	     isn't set (see the set command below), references to `..' in dir
	     are relative to the path used to get to the directory.  If the -P
	     option (physical path) is used or if the physical option is set,
	     `..' is relative to the filesystem directory tree.	 The PWD and
	     OLDPWD parameters are updated to reflect the current and old
	     working directory, respectively.

     cd [-LP] old new
	     The string new is substituted for old in the current directory,
	     and the shell attempts to change to the new directory.

     command [-p] cmd [arg ...]
	     cmd is executed exactly as if command had not been specified,
	     with two exceptions: firstly, cmd cannot be a shell function; and
	     secondly, special built-in commands lose their specialness (i.e.
	     redirection and utility errors do not cause the shell to exit,
	     and command assignments are not permanent).

	     If the -p option is given, a default search path is used instead
	     of the current value of PATH (the actual value of the default
	     path is system dependent: on POSIX-ish systems, it is the value
	     returned by getconf CS_PATH).

     continue [level]
	     Jumps to the beginning of the levelth inner-most for, until, or
	     while loop.  level defaults to 1.

     echo [-Een] [arg ...]
	     Prints its arguments (separated by spaces) followed by a newline,
	     to the standard output.  The newline is suppressed if any of the
	     arguments contain the backslash sequence `\c'.  See the print
	     command below for a list of other backslash sequences that are

	     The options are provided for compatibility with BSD shell
	     scripts.  The -n option suppresses the trailing newline, -e
	     enables backslash interpretation (a no-op, since this is normally
	     done), and -E suppresses backslash interpretation.	 If the posix
	     option is set, only the first argument is treated as an option,
	     and only if it is exactly ``-n''.

     eval command ...
	     The arguments are concatenated (with spaces between them) to form
	     a single string which the shell then parses and executes in the
	     current environment.

     exec [command [arg ...]]
	     The command is executed without forking, replacing the shell

	     If no command is given except for I/O redirection, the I/O
	     redirection is permanent and the shell is not replaced.  Any file
	     descriptors which are opened or dup(2)'d in this way are made
	     available to other executed commands (note that the Korn shell
	     differs here: it does not pass on file descriptors greater than

     exit [status]
	     The shell exits with the specified exit status.  If status is not
	     specified, the exit status is the current value of the $?

     export [-p] [parameter[=value]]
	     Sets the export attribute of the named parameters.	 Exported
	     parameters are passed in the environment to executed commands.
	     If values are specified, the named parameters are also assigned.

	     If no parameters are specified, the names of all parameters with
	     the export attribute are printed one per line, unless the -p
	     option is used, in which case export commands defining all
	     exported parameters, including their values, are printed.

     false   A command that exits with a non-zero status.

     fc -e - | -s [-g] [old=new] [prefix]
	     Re-execute the selected command (the previous command by default)
	     after performing the optional substitution of old with new.  If
	     -g is specified, all occurrences of old are replaced with new.
	     The meaning of -e - and -s is identical: re-execute the selected
	     command without invoking an editor.  This command is usually
	     accessed with the predefined alias r='fc -e -'.

     fg [job ...]
	     Resume the specified job(s) in the foreground.  If no jobs are
	     specified, %+ is assumed.	See Job control below for more

     getopts optstring name [arg ...]
	     Used by shell procedures to parse the specified arguments (or
	     positional parameters, if no arguments are given) and to check
	     for legal options.	 optstring contains the option letters that
	     getopts is to recognize.  If a letter is followed by a colon, the
	     option is expected to have an argument.  Options that do not take
	     arguments may be grouped in a single argument.  If an option
	     takes an argument and the option character is not the last
	     character of the argument it is found in, the remainder of the
	     argument is taken to be the option's argument; otherwise, the
	     next argument is the option's argument.

	     Each time getopts is invoked, it places the next option in the
	     shell parameter name and the index of the argument to be
	     processed by the next call to getopts in the shell parameter
	     OPTIND.  If the option was introduced with a `+', the option
	     placed in name is prefixed with a `+'.  When an option requires
	     an argument, getopts places it in the shell parameter OPTARG.

	     When an illegal option or a missing option argument is
	     encountered, a question mark or a colon is placed in name
	     (indicating an illegal option or missing argument, respectively)
	     and OPTARG is set to the option character that caused the
	     problem.  Furthermore, if optstring does not begin with a colon,
	     a question mark is placed in name, OPTARG is unset, and an error
	     message is printed to standard error.

	     When the end of the options is encountered, getopts exits with a
	     non-zero exit status.  Options end at the first (non-option
	     argument) argument that does not start with a `-', or when a `--'
	     argument is encountered.

	     Option parsing can be reset by setting OPTIND to 1 (this is done
	     automatically whenever the shell or a shell procedure is

	     Warning: Changing the value of the shell parameter OPTIND to a
	     value other than 1, or parsing different sets of arguments
	     without resetting OPTIND, may lead to unexpected results.

     hash [-r] [name ...]
	     Without arguments, any hashed executable command pathnames are
	     listed.  The -r option causes all hashed commands to be removed
	     from the hash table.  Each name is searched as if it were a
	     command name and added to the hash table if it is an executable

     jobs [-lnp] [job ...]
	     Display information about the specified job(s); if no jobs are
	     specified, all jobs are displayed.	 The -n option causes
	     information to be displayed only for jobs that have changed state
	     since the last notification.  If the -l option is used, the
	     process ID of each process in a job is also listed.  The -p
	     option causes only the process group of each job to be printed.
	     See Job control below for the format of job and the displayed

     kill [-s signame | -signum | -signame] { job | pid | pgrp } ...
	     Send the specified signal to the specified jobs, process IDs, or
	     process groups.  If no signal is specified, the TERM signal is
	     sent.  If a job is specified, the signal is sent to the job's
	     process group.  See Job control below for the format of job.

     kill -l [exit-status ...]
	     Print the signal name corresponding to exit-status.  If no
	     arguments are specified, a list of all the signals, their
	     numbers, and a short description of them are printed.

     print [-nrsu[n] | -R [-en]] [argument ...]
	     print prints its arguments on the standard output, separated by
	     spaces and terminated with a newline.  The -n option suppresses
	     the newline.  By default, certain C escapes are translated.
	     These include `\b', `\f', `\n', `\r', `\t', `\v', and `\0###'
	     (`#' is an octal digit, of which there may be 0 to 3).  `\c' is
	     equivalent to using the -n option.	 `\' expansion may be
	     inhibited with the -r option.  The -s option prints to the
	     history file instead of standard output; and the -u option prints
	     to file descriptor n (n defaults to 1 if omitted).

	     The -R option is used to emulate, to some degree, the BSD echo(1)
	     command, which does not process `\' sequences unless the -e
	     option is given.  As above, the -n option suppresses the trailing

     pwd [-LP]
	     Print the present working directory.  If the -L option is used or
	     if the physical option isn't set (see the set command below), the
	     logical path is printed (i.e. the path used to cd to the current
	     directory).  If the -P option (physical path) is used or if the
	     physical option is set, the path determined from the filesystem
	     (by following `..' directories to the root directory) is printed.

     read [-rsu[n]] [parameter ...]
	     Reads a line of input from the standard input, separates the line
	     into fields using the IFS parameter (see Substitution above), and
	     assigns each field to the specified parameters.  If there are
	     more parameters than fields, the extra parameters are set to
	     NULL, or alternatively, if there are more fields than parameters,
	     the last parameter is assigned the remaining fields (inclusive of
	     any separating spaces).  If no parameters are specified, the
	     REPLY parameter is used.  If the input line ends in a backslash
	     and the -r option was not used, the backslash and the newline are
	     stripped and more input is read.  If no input is read, read exits
	     with a non-zero status.

	     The first parameter may have a question mark and a string
	     appended to it, in which case the string is used as a prompt
	     (printed to standard error before any input is read) if the input
	     is a tty(4) (e.g. read nfoo?'number of foos: ').

	     The -un option causes input to be read from file descriptor n (n
	     defaults to 0 if omitted).	 If the -s option is used, input is
	     saved to the history file.

     readonly [-p] [parameter [=value] ...]
	     Sets the read-only attribute of the named parameters.  If values
	     are given, parameters are set to them before setting the
	     attribute.	 Once a parameter is made read-only, it cannot be
	     unset and its value cannot be changed.

	     If no parameters are specified, the names of all parameters with
	     the read-only attribute are printed one per line, unless the -p
	     option is used, in which case readonly commands defining all
	     read-only parameters, including their values, are printed.

     return [status]
	     Returns from a function or . script, with exit status status.  If
	     no status is given, the exit status of the last executed command
	     is used.  If used outside of a function or . script, it has the
	     same effect as exit.  Note that pdksh treats both profile and ENV
	     files as . scripts, while the original Korn shell only treats
	     profiles as . scripts.

     set [+-abCefhkmnpsuvXx] [+-o option] [+-A name] [--] [arg ...]
	     The set command can be used to set (-) or clear (+) shell
	     options, set the positional parameters, or set an array
	     parameter.	 Options can be changed using the +-o option syntax,
	     where option is the long name of an option, or using the +-letter
	     syntax, where letter is the option's single letter name (not all
	     options have a single letter name).  The following table lists
	     both option letters (if they exist) and long names along with a
	     description of what the option does:

	     -A name	      Sets the elements of the array parameter name to
			      arg ... If -A is used, the array is reset (i.e.
			      emptied) first; if +A is used, the first N
			      elements are set (where N is the number of
			      arguments); the rest are left untouched.

	     -a | allexport   All new parameters are created with the export

	     -b | notify      Print job notification messages asynchronously,
			      instead of just before the prompt.  Only used if
			      job control is enabled (-m).

	     -C | noclobber   Prevent > redirection from overwriting existing
			      files.  Instead, >| must be used to force an

	     -e | errexit     Exit (after executing the ERR trap) as soon as
			      an error occurs or a command fails (i.e. exits
			      with a non-zero status).	This does not apply to
			      commands whose exit status is explicitly tested
			      by a shell construct such as if, until, while,
			      &&, ||, or ! statements.

	     -f | noglob      Do not expand file name patterns.

	     -h | trackall    Create tracked aliases for all executed commands
			      (see Aliases above).  Enabled by default for
			      non-interactive shells.

	     -k | keyword     Parameter assignments are recognized anywhere in
			      a command.

	     -m | monitor     Enable job control (default for interactive

	     -n | noexec      Do not execute any commands.  Useful for
			      checking the syntax of scripts (ignored if

	     -p | privileged  The shell is a privileged shell.	It is set
			      automatically if, when the shell starts, the
			      real UID or GID does not match the effective UID
			      (EUID) or GID (EGID), respectively.  See above
			      for a description of what this means.

	     -s | stdin	      If used when the shell is invoked, commands are
			      read from standard input.	 Set automatically if
			      the shell is invoked with no arguments.

			      When -s is used with the set command it causes
			      the specified arguments to be sorted before
			      assigning them to the positional parameters (or
			      to array name, if -A is used).

	     -u | nounset     Referencing of an unset parameter is treated as
			      an error, unless one of the `-', `+', or `='
			      modifiers is used.

	     -v | verbose     Write shell input to standard error as it is

	     -X | markdirs    Mark directories with a trailing `/' during file
			      name generation.

	     -x | xtrace      Print commands and parameter assignments when
			      they are executed, preceded by the value of PS4.

	     bgnice	      Background jobs are run with lower priority.

	     ignoreeof	      The shell will not exit when end-of-file is
			      read; exit must be used.

	     interactive      The shell is an interactive shell.  This option
			      can only be used when the shell is invoked.  See
			      above for a description of what this means.

	     login	      The shell is a login shell.  This option can
			      only be used when the shell is invoked.  See
			      above for a description of what this means.

	     nohup	      Do not kill running jobs with a SIGHUP signal
			      when a login shell exits.	 Currently set by
			      default, but this will change in the future to
			      be compatible with the original Korn shell
			      (which doesn't have this option, but does send
			      the SIGHUP signal).

	     nolog	      No effect.  In the original Korn shell, this
			      prevents function definitions from being stored
			      in the history file.

	     physical	      Causes the cd and pwd commands to use
			      ``physical'' (i.e. the filesystem's) `..'
			      directories instead of ``logical'' directories
			      (i.e. the shell handles `..', which allows the
			      user to be oblivious of symbolic links to
			      directories).  Clear by default.	Note that
			      setting this option does not affect the current
			      value of the PWD parameter; only the cd command
			      changes PWD.  See the cd and pwd commands above
			      for more details.

	     posix	      Enable POSIX mode.  See POSIX mode above.

	     restricted	      The shell is a restricted shell.	This option
			      can only be used when the shell is invoked.  See
			      above for a description of what this means.

	     vi		      Enable vi(1)-like command-line editing
			      (interactive shells only).

	     vi-esccomplete   In vi command-line editing, do command and file
			      name completion when escape (^[) is entered in
			      command mode.

	     vi-show8	      Prefix characters with the eighth bit set with
			      `M-'.  If this option is not set, characters in
			      the range 128-160 are printed as is, which may
			      cause problems.

	     vi-tabcomplete   In vi command-line editing, do command and file
			      name completion when tab (^I) is entered in
			      insert mode.

	     viraw	      No effect.  In the original Korn shell, unless
			      viraw was set, the vi command-line mode would
			      let the tty(4) driver do the work until ESC (^[)
			      was entered.  pdksh is always in viraw mode.

	     These options can also be used upon invocation of the shell.  The
	     current set of options (with single letter names) can be found in
	     the parameter `$-'.  set -o with no option name will list all the
	     options and whether each is on or off; set +o will print the long
	     names of all options that are currently on.

	     Remaining arguments, if any, are positional parameters and are
	     assigned, in order, to the positional parameters (i.e. $1, $2,
	     etc.).  If options end with `--' and there are no remaining
	     arguments, all positional parameters are cleared.	If no options
	     or arguments are given, the values of all names are printed.  For
	     unknown historical reasons, a lone `-' option is treated
	     specially - it clears both the -x and -v options.

     shift [number]
	     The positional parameters number+1, number+2, etc. are renamed to
	     `1', `2', etc.  number defaults to 1.

     test expression
     [ expression ]
	     test evaluates the expression and returns zero status if true, 1
	     if false, or greater than 1 if there was an error.	 It is
	     normally used as the condition command of if and while
	     statements.  Symbolic links are followed for all file expressions
	     except -h and -L.

	     The following basic expressions are available:

	     -a file		file exists.

	     -b file		file is a block special device.

	     -c file		file is a character special device.

	     -d file		file is a directory.

	     -e file		file exists.

	     -f file		file is a regular file.

	     -G file		file's group is the shell's effective group

	     -g file		file's mode has the setgid bit set.

	     -h file		file is a symbolic link.

	     -k file		file's mode has the sticky(8) bit set.

	     -L file		file is a symbolic link.

	     -O file		file's owner is the shell's effective user ID.

	     -o option		Shell option is set (see the set command above
				for a list of options).	 As a non-standard
				extension, if the option starts with a `!',
				the test is negated; the test always fails if
				option doesn't exist (so [ -o foo -o -o !foo ]
				returns true if and only if option foo

	     -p file		file is a named pipe.

	     -r file		file exists and is readable.

	     -S file		file is a unix(4)-domain socket.

	     -s file		file is not empty.

	     -t [fd]		File descriptor fd is a tty(4) device.	If the
				posix option is not set, fd may be left out,
				in which case it is taken to be 1 (the
				behaviour differs due to the special POSIX
				rules described above).

	     -u file		file's mode has the setuid bit set.

	     -w file		file exists and is writable.

	     -x file		file exists and is executable.

	     file1 -nt file2	file1 is newer than file2.

	     file1 -ot file2	file1 is older than file2.

	     file1 -ef file2	file1 is the same file as file2.

	     string		string has non-zero length.

	     -n string		string is not empty.

	     -z string		string is empty.

	     string = string	Strings are equal.

	     string != string	Strings are not equal.

	     number -eq number	Numbers compare equal.

	     number -ne number	Numbers compare not equal.

	     number -ge number	Numbers compare greater than or equal.

	     number -gt number	Numbers compare greater than.

	     number -le number	Numbers compare less than or equal.

	     number -lt number	Numbers compare less than.

	     The above basic expressions, in which unary operators have
	     precedence over binary operators, may be combined with the
	     following operators (listed in increasing order of precedence):

		   expr -o expr		   Logical OR.
		   expr -a expr		   Logical AND.
		   ! expr		   Logical NOT.
		   ( expr )		   Grouping.

	     On operating systems not supporting /dev/fd/n devices (where n is
	     a file descriptor number), the test command will attempt to fake
	     it for all tests that operate on files (except the -e test).  For
	     example, [ -w /dev/fd/2 ] tests if file descriptor 2 is writable.

	     Note that some special rules are applied (courtesy of POSIX) if
	     the number of arguments to test or [ ... ] is less than five: if
	     leading `!' arguments can be stripped such that only one argument
	     remains then a string length test is performed (again, even if
	     the argument is a unary operator); if leading `!' arguments can
	     be stripped such that three arguments remain and the second
	     argument is a binary operator, then the binary operation is
	     performed (even if the first argument is a unary operator,
	     including an unstripped `!').

	     Note: A common mistake is to use ``if [ $foo = bar ]'', which
	     fails if parameter ``foo'' is NULL or unset, if it has embedded
	     spaces (i.e. IFS characters), or if it is a unary operator like
	     `!' or `-n'.  Use tests like ``if [ "X$foo" = Xbar ]'' instead.

     times   Print the accumulated user and system times used both by the
	     shell and by processes that the shell started which have exited.
	     The format of the output is:

		   0m0.00s 0m0.00s
		   0m0.00s 0m0.00s

     trap [handler signal ...]
	     Sets a trap handler that is to be executed when any of the
	     specified signals are received.  handler is either a NULL string,
	     indicating the signals are to be ignored, a minus sign (`-'),
	     indicating that the default action is to be taken for the signals
	     (see signal(3)), or a string containing shell commands to be
	     evaluated and executed at the first opportunity (i.e. when the
	     current command completes, or before printing the next PS1
	     prompt) after receipt of one of the signals.  signal is the name
	     of a signal (e.g. PIPE or ALRM) or the number of the signal (see
	     the kill -l command above).

	     There are two special signals: EXIT (also known as 0), which is
	     executed when the shell is about to exit, and ERR, which is
	     executed after an error occurs (an error is something that would
	     cause the shell to exit if the -e or errexit option were set -
	     see the set command above).  EXIT handlers are executed in the
	     environment of the last executed command.	Note that for non-
	     interactive shells, the trap handler cannot be changed for
	     signals that were ignored when the shell started.

	     With no arguments, trap lists, as a series of trap commands, the
	     current state of the traps that have been set since the shell
	     started.  Note that the output of trap cannot be usefully piped
	     to another process (an artifact of the fact that traps are
	     cleared when subprocesses are created).

	     The original Korn shell's DEBUG trap and the handling of ERR and
	     EXIT traps in functions are not yet implemented.

     true    A command that exits with a zero value.

     typeset [[+-lprtUux] [-L[n]] [-R[n]] [-Z[n]] [-i[n]] | -f [-tux]] [name
	      [=value] ...]
	     Display or set parameter attributes.  With no name arguments,
	     parameter attributes are displayed; if no options are used, the
	     current attributes of all parameters are printed as typeset
	     commands; if an option is given (or `-' with no option letter),
	     all parameters and their values with the specified attributes are
	     printed; if options are introduced with `+', parameter values are
	     not printed.

	     If name arguments are given, the attributes of the named
	     parameters are set (-) or cleared (+).  Values for parameters may
	     optionally be specified.  If typeset is used inside a function,
	     any newly created parameters are local to the function.

	     When -f is used, typeset operates on the attributes of functions.
	     As with parameters, if no name arguments are given, functions are
	     listed with their values (i.e. definitions) unless options are
	     introduced with `+', in which case only the function names are

	     -f	     Function mode.  Display or set functions and their
		     attributes, instead of parameters.

	     -i[n]   Integer attribute.	 n specifies the base to use when
		     displaying the integer (if not specified, the base given
		     in the first assignment is used).	Parameters with this
		     attribute may be assigned values containing arithmetic

	     -L[n]   Left justify attribute.  n specifies the field width.  If
		     n is not specified, the current width of a parameter (or
		     the width of its first assigned value) is used.  Leading
		     whitespace (and zeros, if used with the -Z option) is
		     stripped.	If necessary, values are either truncated or
		     space padded to fit the field width.

	     -l	     Lower case attribute.  All upper case characters in
		     values are converted to lower case.  (In the original
		     Korn shell, this parameter meant ``long integer'' when
		     used with the -i option.)

	     -p	     Print complete typeset commands that can be used to re-
		     create the attributes (but not the values) of parameters.
		     This is the default action (option exists for ksh93

	     -R[n]   Right justify attribute.  n specifies the field width.
		     If n is not specified, the current width of a parameter
		     (or the width of its first assigned value) is used.
		     Trailing whitespace is stripped.  If necessary, values
		     are either stripped of leading characters or space padded
		     to make them fit the field width.

	     -r	     Read-only attribute.  Parameters with this attribute may
		     not be assigned to or unset.  Once this attribute is set,
		     it cannot be turned off.

	     -t	     Tag attribute.  Has no meaning to the shell; provided for
		     application use.

		     For functions, -t is the trace attribute.	When functions
		     with the trace attribute are executed, the xtrace (-x)
		     shell option is temporarily turned on.

	     -U	     Unsigned integer attribute.  Integers are printed as
		     unsigned values (only useful when combined with the -i
		     option).  This option is not in the original Korn shell.

	     -u	     Upper case attribute.  All lower case characters in
		     values are converted to upper case.  (In the original
		     Korn shell, this parameter meant ``unsigned integer''
		     when used with the -i option, which meant upper case
		     letters would never be used for bases greater than 10.
		     See the -U option.)

		     For functions, -u is the undefined attribute.  See
		     Functions above for the implications of this.

	     -x	     Export attribute.	Parameters (or functions) are placed
		     in the environment of any executed commands.  Exported
		     functions are not yet implemented.

	     -Z[n]   Zero fill attribute.  If not combined with -L, this is
		     the same as -R, except zero padding is used instead of
		     space padding.

     ulimit [-acdfHlmnpSst [value]] ...
	     Display or set process limits.  If no options are used, the file
	     size limit (-f) is assumed.  value, if specified, may be either
	     an arithmetic expression starting with a number or the word
	     ``unlimited''.  The limits affect the shell and any processes
	     created by the shell after a limit is imposed; limits may not be
	     increased once they are set.

	     -a	    Display all limits; unless -H is used, soft limits are

	     -c n   Impose a size limit of n blocks on the size of core dumps.

	     -d n   Impose a size limit of n kilobytes on the size of the data

	     -f n   Impose a size limit of n blocks on files written by the
		    shell and its child processes (files of any size may be

	     -H	    Set the hard limit only (the default is to set both hard
		    and soft limits).

	     -l n   Impose a limit of n kilobytes on the amount of locked
		    (wired) physical memory.

	     -m n   Impose a limit of n kilobytes on the amount of physical
		    memory used.

	     -n n   Impose a limit of n file descriptors that can be open at

	     -p n   Impose a limit of n processes that can be run by the user
		    at any one time.

	     -S	    Set the soft limit only (the default is to set both hard
		    and soft limits).

	     -s n   Impose a size limit of n kilobytes on the size of the
		    stack area.

	     -t n   Impose a time limit of n CPU seconds spent in user mode to
		    be used by each process.

	     As far as ulimit is concerned, a block is 512 bytes.

     umask [-S] [mask]
	     Display or set the file permission creation mask, or umask (see
	     umask(2)).	 If the -S option is used, the mask displayed or set
	     is symbolic; otherwise, it is an octal number.

	     Symbolic masks are like those used by chmod(1).  When used, they
	     describe what permissions may be made available (as opposed to
	     octal masks in which a set bit means the corresponding bit is to
	     be cleared).  For example, ``ug=rwx,o='' sets the mask so files
	     will not be readable, writable, or executable by ``others'', and
	     is equivalent (on most systems) to the octal mask ``007''.

     unalias [-adt] [name ...]
	     The aliases for the given names are removed.  If the -a option is
	     used, all aliases are removed.  If the -t or -d options are used,
	     the indicated operations are carried out on tracked or directory
	     aliases, respectively.

     unset [-fv] parameter ...
	     Unset the named parameters (-v, the default) or functions (-f).
	     The exit status is non-zero if any of the parameters have the
	     read-only attribute set, zero otherwise.

     wait [job ...]
	     Wait for the specified job(s) to finish.  The exit status of wait
	     is that of the last specified job; if the last job is killed by a
	     signal, the exit status is 128 + the number of the signal (see
	     kill -l exit-status above); if the last specified job can't be
	     found (because it never existed, or had already finished), the
	     exit status of wait is 127.  See Job control below for the format
	     of job.  wait will return if a signal for which a trap has been
	     set is received, or if a SIGHUP, SIGINT, or SIGQUIT signal is

	     If no jobs are specified, wait waits for all currently running
	     jobs (if any) to finish and exits with a zero status.  If job
	     monitoring is enabled, the completion status of jobs is printed
	     (this is not the case when jobs are explicitly specified).

     whence [-pv] [name ...]
	     For each name, the type of command is listed (reserved word,
	     built-in, alias, function, tracked alias, or executable).	If the
	     -p option is used, a path search is performed even if name is a
	     reserved word, alias, etc.	 Without the -v option, whence is
	     similar to command -v except that whence will find reserved words
	     and won't print aliases as alias commands.	 With the -v option,
	     whence is the same as command -V.	Note that for whence, the -p
	     option does not affect the search path used, as it does for
	     command.  If the type of one or more of the names could not be
	     determined, the exit status is non-zero.

   Job control
     Job control refers to the shell's ability to monitor and control jobs,
     which are processes or groups of processes created for commands or
     pipelines.	 At a minimum, the shell keeps track of the status of the
     background (i.e. asynchronous) jobs that currently exist; this
     information can be displayed using the jobs commands.  If job control is
     fully enabled (using set -m or set -o monitor), as it is for interactive
     shells, the processes of a job are placed in their own process group.
     Foreground jobs can be stopped by typing the suspend character from the
     terminal (normally ^Z), jobs can be restarted in either the foreground or
     background using the fg and bg commands, and the state of the terminal is
     saved or restored when a foreground job is stopped or restarted,

     Note that only commands that create processes (e.g. asynchronous
     commands, subshell commands, and non-built-in, non-function commands) can
     be stopped; commands like read cannot be.

     When a job is created, it is assigned a job number.  For interactive
     shells, this number is printed inside ``[..]'', followed by the process
     IDs of the processes in the job when an asynchronous command is run.  A
     job may be referred to in the bg, fg, jobs, kill, and wait commands
     either by the process ID of the last process in the command pipeline (as
     stored in the $! parameter) or by prefixing the job number with a percent
     sign (`%').  Other percent sequences can also be used to refer to jobs:

     %+ | %% | %    The most recently stopped job, or, if there are no stopped
		    jobs, the oldest running job.

     %-		    The job that would be the %+ job if the latter did not

     %n		    The job with job number n.

     %?string	    The job with its command containing the string string (an
		    error occurs if multiple jobs are matched).

     %string	    The job with its command starting with the string string
		    (an error occurs if multiple jobs are matched).

     When a job changes state (e.g. a background job finishes or foreground
     job is stopped), the shell prints the following status information:

	   [number] flag status command


     number   is the job number of the job;

     flag     is the `+' or `-' character if the job is the %+ or %- job,
	      respectively, or space if it is neither;

     status   indicates the current state of the job and can be:

	      Done [number]
			 The job exited.  number is the exit status of the
			 job, which is omitted if the status is zero.

	      Running	 The job has neither stopped nor exited (note that
			 running does not necessarily mean consuming CPU time
			 - the process could be blocked waiting for some

	      Stopped [signal]
			 The job was stopped by the indicated signal (if no
			 signal is given, the job was stopped by SIGTSTP).

	      signal-description [``core dumped'']
			 The job was killed by a signal (e.g. memory fault,
			 hangup); use kill -l for a list of signal
			 descriptions.	The ``core dumped'' message indicates
			 the process created a core file.

     command  is the command that created the process.	If there are multiple
	      processes in the job, each process will have a line showing its
	      command and possibly its status, if it is different from the
	      status of the previous process.

     When an attempt is made to exit the shell while there are jobs in the
     stopped state, the shell warns the user that there are stopped jobs and
     does not exit.  If another attempt is immediately made to exit the shell,
     the stopped jobs are sent a SIGHUP signal and the shell exits.
     Similarly, if the nohup option is not set and there are running jobs when
     an attempt is made to exit a login shell, the shell warns the user and
     does not exit.  If another attempt is immediately made to exit the shell,
     the running jobs are sent a SIGHUP signal and the shell exits.

     ~/.profile		  User's login profile.
     /etc/profile	  System login profile.
     /etc/suid_profile	  Privileged shell profile.
     /etc/shells	  Shell database.

     csh(1), ed(1), ksh(1), mg(1), stty(1), vi(1), shells(5), environ(7),

     Morris Bolsky and David Korn, The KornShell Command and Programming
     Language, 1983, ISBN 0-13-516972-0.

     Stephen G. Kochan and Patrick H. Wood, UNIX Shell Programming, Hayden.

     IEEE Inc., IEEE Standard for Information Technology - Portable Operating
     System Interface (POSIX) - Part 2: Shell and Utilities, 1993, ISBN

     sh is implemented as a run-time option of pdksh, with only those sh
     features whose syntax or semantics are incompatible with a traditional
     Bourne shell disabled.  Since this leaves some sh extensions exposed,
     caution should be used where backwards compatibility with traditional
     Bourne or POSIX compliant shells is an issue.

     This shell is based on the public domain 7th edition Bourne shell clone
     by Charles Forsyth and parts of the BRL shell by Doug A. Gwyn, Doug
     Kingston, Ron Natalie, Arnold Robbins, Lou Salkind, and others.  The
     first release of pdksh was created by Eric Gisin, and it was subsequently
     maintained by John R. MacMillan (change!, Simon J. Gerraty
     (, and Michael Rendell (  The
     CONTRIBUTORS file in the source distribution contains a more complete
     list of people and their part in the shell's development.

OpenBSD 4.9		      September 20, 2010		   OpenBSD 4.9

List of man pages available for OpenBSD

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