ksh(C)

Syntax

rksh [ ±aefhikmnoprstuvx ] [ ±o option ] ... [ -c string ] [ arg ... ]

Description

The Korn shell ksh is a command interpreter; it reads input typed at a terminal (or saved in a file) and interprets the commands it encounters on each line. In addition to executing named programs, the Korn shell incorporates a high-level programming language that can be used to automate the execution of other programs. The Korn shell language is a superset of that defined by the Bourne shell sh; see sh(C) for details.

NOTE: /bin/posix/sh, linked to ksh, supplies the functionality for sh(C) and echo(C), as defined by ISO/IEC DIS 99452:1992, Information technology Portable Operating System Interface (POSIX) Part 2: Shell and Utilities (IEEE Std 1003.21992) and X/Open CAE Specification, Commands and Utilities, Issue 4, 1992.

The Korn shell has built-in TCP/IP functionality. See ``TCP/IP functionality''.

The Korn shell incorporates interactive command editing facilities, which make it easier to work with than the Bourne shell; see ``In-line editing options''.

rksh is a restricted version of the command interpreter ksh; it is used to set up login names and execution environments with capabilities more restricted than those of the standard shell.

See ``Invocation'' for the meaning of arguments to the shell.

Definitions

A metacharacter is one of the following characters:

; & ( ) | < > newline space tab

A blank is a space or a tab.

An identifier is a sequence of letters, digits, or underscores starting with a letter or underscore. Identifiers are used as names for functions and named parameters.

A word is a sequence of characters separated by one or more non-quoted metacharacters.

TCP/IP functionality

If ksh is asked to open a filename of the above type by means of an I/O redirection operator (``<'', ``>'', or ``>>''), the shell attempts to open a TCP or UDP connection to port-number at IP-address. Only numeric IP addresses and port numbers may be used; hostnames and service names may not be used.

A connection opened in this fashion is always opened for read and write, regardless of the redirection operator that was used.

The following example retrieves and prints the contents of the web page at the http://localhost/index.html URL:

   { print -u3 "GET /index.html HTTP/1.0\n"; cat <&3; } 3</dev/tcp/127.0.0.1/80

In-line editing options

When in an editing mode, the shell behaves like a text editor with a window one line high (that line being the current shell prompt line). It is possible to scroll the window up or down through a history file containing all the previously issued commands, and to edit or execute any of those commands. It is also possible to type and issue a new command, which is then appended to the history file.

The window width in characters is the value of COLUMNS if it is defined, otherwise 80. If the line is longer than the window width minus two, a mark is displayed at the end of the window to notify the user. As the cursor moves and reaches the window boundaries the window will be centered about the cursor. The mark is a ``>'' if the line extends on the right side of the window; < if it extends on the left; if it extends on both.

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

The editing features require that the user's terminal accept <Enter> as a carriage return without line feed and that a space `` '' must overwrite the current character on the screen. ADM terminal users should set the ``space - advance'' switch to `space'. Hewlett-Packard<sup>®</sup> Series 2621 terminal users should set the straps to `bcGHxZ etX'.

vi editing mode

There are two typing modes. Initially, when you enter a command you are in the input mode. To edit, enter the control mode by typing <Esc> (ASCII 033) and move the cursor to the point needing correction and then insert or delete characters or words as needed. Most control commands accept an optional repeat count prior to the command.

When in vi mode on most systems, canonical processing is initially enabled and the command is echoed again if it contains any control characters and the speed is 1200 baud or greater, or if less than one second has elapsed since the prompt was printed. The <Esc> character terminates canonical processing for the remainder of the command and the user can then modify the command line. This scheme has the advantages of canonical processing with the type-ahead echoing of raw mode.

If the option viraw is also set, the terminal always has canonical processing disabled. This may be helpful for certain terminals.

Input edit commands

erase

Delete the previous character. This is the user-defined erase character as defined by the stty(C) command, usually ^H or #.

^W

Delete the previous blank-separated word.

^D

End of file, if it is the first character on a line. The shell interprets this as indicating that there is no more input to read from the terminal. This terminates the shell unless ignoreeof is set.

^V

Escape the next character. Editing characters and the user's erase and kill characters may be entered in a command line or in a search string if preceded by a ^V. ^V removes the next character's editing features (if any).

\

Escape the next erase or kill character.

Motion edit commands

[count]l

Move the cursor forward (right) one character.

[count]w

Move the cursor forward one alpha-numeric word.

[count]W

Move the cursor to the beginning of the next word that follows a blank.

[count]e

Move the cursor to the end of the word.

[count]E

Move the cursor to the end of the current blank delimited word.

[count]h

Move the cursor backward (left) one character.

[count]b

Move the cursor backward one word.

[count]B

Move the cursor to the preceding blank-separated word.

[count]|

Move the cursor to the column count.

[count]fc

Find the next character c in the current line.

[count]Fc

Find the previous character c in the current line.

[count]tc

Equivalent to f followed by h.

[count]Tc

Equivalent to F followed by l.

[count];

Repeat count times, the last single-character find command, f, F, t, or T.

[count],

Reverse the last single-character find command count times.

0

Move the cursor to the start of the line.

^

Move the cursor to the first non-blank character in the line.

$

Move the cursor to the end of the line.

Search edit commands

[count]k

Fetch the previous command.

[count]-

Equivalent to k.

[count]j

Fetch the next command.

[count]+

Equivalent to j.

[count]G

Fetch the command number count. The default is the least recent command.

/string

Search backward for a command containing string. string is terminated by a <Enter> or a linefeed character (/n). If string is preceded by a ``^'', the matched line must begin with string. If string is null the previous string is used.

?string

Same as ``/'' except that the search is in the forward direction.

n

Search for the next match of the last ``/'' or ``?'' command.

N

Search for the next match of the last ``/'' or ``?'' commands, but in the reverse direction. Search the history for the string entered by the previous ``/'' command.

Text modification edit commands

a

Enter input mode and enter text after the current character.

A

Append text to the end of the line. Equivalent to $a.

[count]cmotion
c[count]motion

Delete from the current character through the character to which motion moves the cursor and enter input mode. If motion is ``c'', the entire line is deleted.

C

Delete from the current character through the end of the line and enter input mode. Equivalent to c$.

S

Equivalent to cc.

D

Delete from the current character through the end of the line. Equivalent to d$.

[count]dmotion
d[count]motion

Delete the current character through the character to which motion moves. If motion is ``d'', the entire line is deleted.

i

Enter input mode and insert text before the current character.

I

Insert text before the beginning of the line. Equivalent to 0i.

[count]P

Place the previous text modification before the cursor.

[count]p

Place the previous text modification after the cursor.

R

Enter input mode and replace characters on the screen with characters typed overlay fashion.

[count]rc

Replace the count character(s) starting at the current cursor position with c, and advance the cursor.

[count]x

Delete the current character.

[count]X

Delete the preceding character.

[count].

Repeat the previous text modification command.

[count]~

Invert the case of the count character(s) starting at the current cursor position and advance the cursor.

[count]_

Append the count word of the previous command and enter input mode. The last word is used if count is omitted.

*

Append an ``'' to the current word and attempt filename generation. If no match is found, it rings the system bell. Otherwise, the word is replaced by the matching pattern and input mode is entered.

\

Complete filename. The current word is replaced by the longest common prefix of all filenames matching the current word with an ``'' appended. If the match is unique, a ``/'' is appended if the file is a directory and a space is appended if the file is not a directory.

Other edit commands

[count]ymotion
y[count]motion

Yank from the current character through the character to which motion moves the cursor and put them into the delete buffer. The text and cursor are unchanged.

Y

Yank from the current position to the end of the line. Equivalent to y$.

u

Undo the last text modifying command.

U

Undo all the text modifying commands performed on the line.

[count]v

Return the command fc -e ${VISUAL:-${EDITOR:-vi}} count in the input buffer. If count is omitted, then the current line is used.

^L

Line feed and print the current line. This has effect only in control mode.

^J

New line and execute the current line, regardless of mode.

^M

Return and execute the current line, regardless of mode.

\#

Send the line after inserting a ``\#'' in front of the line. This is useful for causing the current line to be inserted in the history without being executed.

=

List the filenames that match the current word if an ``'' were appended to it.

@letter

Search the alias list for an alias by the name _letter and if an alias of this name is defined, insert its value in the input queue for processing.

emacs editing mode

The notation for escape sequences is M- followed by a character. For example, M-f (pronounced Meta f) is entered by depressing <Esc> (ASCII 033) followed by the F key. (M-F would be the notation for <Esc> followed by <Shift> (capital) F.)

All edit commands operate from any place on the line (not just at the beginning). Neither <Enter> nor <Line Feed> is entered after edit commands except when noted.

^F

Move the cursor forward (right) one character.

M-f

Move the cursor forward one word. (In emacs mode, a word is a string of characters consisting only of letters, digits and underscores.)

^B

Move the cursor backward (left) one character.

M-b

Move the cursor backward one word.

^A

Move the cursor to the start of the line.

^E

Move the cursor to the end of the line.

^]char

Move the cursor forward to the character char on the current line.

M-^]char

Move the cursor back to the character char on the current line.

^X^X

Interchange the cursor and mark.

erase

(This is the user-defined erase character as defined by the stty(C) command, usually ^H or #.) Delete the previous character.

^D

Delete the current character.

M-d

Delete the current word.

M-^H

(Meta-backspace) Delete the previous word.

M-h

Delete the previous word.

M-^?

(Meta-<Del>) Delete the previous word (if your interrupt character is ^? (<Del>, the default) then this command will not work).

^T

In emacs mode transpose the current character with the next character. In gmacs mode transpose the two previous characters.

^C

Capitalize the current character.

M-c

Capitalize the current word.

M-l

Change the current word to lowercase.

^K

Delete from the cursor to the end of the line. If it is preceded by a numerical parameter whose value is less than the current cursor position, then delete from the given position up to the cursor. If it is preceded by a numerical parameter whose value is greater than the current cursor position, then delete from the cursor up to the given cursor position.

^W

Kill from the cursor to the mark.

M-p

Push the region from the cursor to the mark onto the stack.

kill

(This is the user-defined kill character as defined by the stty command, usually ^U or @.) Kill the entire current line. If two kill characters are entered in succession, all kill characters from then on cause a line feed (useful when using paper terminals).

^Y

Restore the last item removed from the line. (Yank the item back to the line.)

^L

Line feed and print the current line.

^@

(Null character) Set the mark.

M-space

(Meta space) Set the mark.

^J

(New line) Execute the current line.

^M

(Return) Execute the current line.

eof

The end-of-file character, normally ^D, is processed as an End-of-file only if the current line is null.

^P

Fetch the previous command. It moves back one line when not on the first line of a multi-line command.

M-<

Fetch the least recent (oldest) history line.

M->

Fetch the most recent (youngest) history line.

^N

Fetch the next command line.

^Rstring

Reverse the search history for a previous command line containing string. If a parameter of 0 is given, the search is forward. string is terminated by a <Enter> or /n. If string is preceded by a ``^'', the matched line must begin with string. If string is omitted, then the next command line containing the most recent string is accessed. In this case a parameter of 0 reverses the direction of the search.

^O

Execute the current line and fetch the next line from the history file.

M-digits

Define a numeric parameter. The digits are taken as a parameter to the next command. The commands that accept a parameter are ^F, ^B, erase, ^C, ^D, ^K, ^R, ^P, ^N, ^], M-., M-^], M-_, M-b, M-c, M-d, M-f, M-h, M-l and M-^H.

M-letter

Search alias list for an alias by the name _letter and if an alias of this name is defined, insert its value on the input queue. The letter must not be one of the above meta-functions.

M-]letter

Search alias list for an alias by the name __letter (two underscores precede letter) and if an alias of this name is defined, insert its value on the input queue. This can be used to program function keys on many terminals.

M-.

Insert the last word of the previous command on the line. If preceded by a numeric parameter, the value of this parameter determines which word to insert rather than the last word.

M-_

Same as M-..

M-*

Attempt filename generation on the current word. An ``'' is appended if the word does not match any file or contain any special pattern characters.

M-ESC

Perform filename-completion on the current word. The current word is treated as a root to which an ``'' is appended. A search is conducted for files matching the current word. The first match found then replaces the current word. Subsequent matches are obtained by repeating M-ESC. If the match is both unique and a directory, a ``/'' is appended to it. If it is unique but not a directory, a space is appended to it.

M-=

List the files matching the current word pattern if an ``'' were appended.

^U

Multiply the parameter of the next command by 4.

\

Escape the next character. Editing characters and the user's erase, kill and interrupt (normally ^?) characters may be entered in a command line or in a search string if preceded by a ``\''. The ``\'' removes the next character's editing features (if any).

^V

Display the version of the shell.

M-\#

Insert a ``\#'' at the beginning of the line and execute it. This causes a comment to be inserted in the history file.

History file

re-executes the most recent command which starts with the letter ``c'', replacing the first occurrence of the string bad with the string good.

Commands

The following sections constitute a detailed definition of the Korn shell language.

A special command is a command that is carried out by the shell without creating a separate process. Except for documented side effects, most special commands can be implemented as separate utilities.

A simple command is a sequence of blank-separated words which may be preceded by a parameter assignment list (see ``Environment''). The first word specifies the name of the command to be executed. Except as specified below, the remaining words are passed as arguments to the invoked command. The command name is passed as argument 0 (see exec(S)). The value of a simple-command is its exit status if it terminates normally, or (octal) 200+status if it terminates abnormally (see signal(S) for a list of status values).

A pipeline is a sequence of one or more commands separated by ``|''. The standard output of each command but the last is connected by a pipe(S) to the standard input of the next command. Each command is run in a separate subshell environment except for the last command in the pipeline; the shell waits for the last command to terminate. The exit status of a pipeline is the exit status of the last command.

A list is a sequence of one or more pipelines separated by ; & && or || and optionally terminated by ; & or |&. Of these five symbols, && and || have highest precedence. The following three symbols, ; & and |& are of equal precedence, as are && and ||. A semicolon (;) causes sequential execution of the preceding pipeline; an ampersand (&) causes asynchronous execution of the preceding pipeline (that is, the shell does not wait for that pipeline to finish). The symbol |& causes asynchronous execution of the preceding command or pipeline with a two-way pipe established to the parent shell. The parent shell can write to and read from the standard input and standard output of the spawned command using the -p option of the special commands read and print (described later). The symbol && (||) causes the list following it to be executed only if the preceding pipeline returns a zero (non-zero) value. An arbitrary number of new-lines may appear in a list, instead of a semicolon, to delimit a command.

A command is either a simple-command or one of the following compound-commands. A compound-command is a command that results in the execution of one or more simple-commands, depending upon the state of its input. Unless otherwise stated, the value returned by a command is that of the last simple-command executed in the command.

for identifier [ in word ... ] ;do list ;done

Each time a for command is executed, identifier is set to the next word taken from the in word list. If in word ... is omitted, then the for command executes the do list once for each positional parameter that is set (see ``Parameter substitution''). Execution ends when there are no more words in the list.

select identifier [ in word ... ] ;do list ;done

A select command prints on standard error (file descriptor 2), the set of words, each preceded by a number. If in word ... is omitted, then the positional parameters are used instead (see ``Parameter substitution''). The PS3 prompt is printed and a line is read from the standard input. If this line consists of the number of one of the listed words, then the value of the parameter identifier is set to the word corresponding to this number. If this line is empty the selection list is printed again. Otherwise the value of the parameter identifier is set to null. The contents of the line read from standard input is saved in the parameter REPLY. The list is executed for each selection until a break or an end-of-file is encountered.

case word in [ [(] pattern [ | pattern ] ... ) list ;; ] ... esac

A case command executes the list associated with the first pattern that matches word. The form of the patterns is the same as that used for filename generation (see regexp(M) for details).

if list ;then list [  elif list ;then list ] ... [ ;else list ] ;fi

The list following if is executed and, if it returns a 0 exit status, the list following the first then is executed. Otherwise, the list following elif is executed and, if its value is 0, the list following the next then is executed. Failing that, the else list is executed. If no else list or then list is executed, the if command returns a 0 exit status.

while list ;do list ;done
until list ;do list ;done

A while command repeatedly executes the while list and, if the exit status of the last command in the list is 0, executes the do list; otherwise the loop terminates.

If no commands in the do list are executed, then the while command returns a 0 exit status; until may be used in place of while to negate the loop termination test.

( list )

This executes list in a separate environment. Note that if two adjacent open parentheses are needed for nesting, a space must be inserted to avoid arithmetic evaluation as described below.

{ list ;}

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

[[ expression ]]

This evaluates expression and returns a 0 exit status when expression is true. See ``Conditional expressions'' for a description of expression.

function identifier { list ;}
identifier () { list ;}

This defines a function which is referenced by identifier. The body of the function is the list of commands between ``{'' and ``}''. (See ``Functions''.)

time pipeline

The pipeline is executed and the elapsed time as well as the user and system time are printed on standard error.

Comments

Aliasing

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

Aliases are frequently used as an abbreviation for full pathnames. An option to the aliasing facility allows the value of the alias to be automatically set to the full pathname of the corresponding command. These aliases are called tracked aliases. The value of a tracked alias is defined the first time the corresponding command is looked up and becomes undefined each time the PATH variable is reset. These aliases remain tracked so that the next reference redefines the value. Several tracked aliases are compiled into the shell. The -h option of the set command makes each referenced command name into a tracked alias.

The following exported aliases are compiled into the shell but can be unset or redefined:

autoload='typeset -fu'
functions='typeset -f'
history='fc -l'
integer='typeset -i'
nohup='nohup '
r='fc -e -'

(The alias of nohup with a trailing space allows nohup to be used with aliased commands.)

Tilde substitution

In addition, tilde substitution is attempted when the value of a variable assignment parameter begins with a ``~''.

Command substitution

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

Process substitution

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

NOTE: This feature is available on SCO OpenServer systems and other versions of the UNIX operating system that support the /dev/fd directory for naming open files. Programs which make use of this feature may not be portable to UNIX systems which do not support the /dev/fd feature.

Parameter substitution

The shell supports a one-dimensional array facility. An element of an array parameter is referenced by a subscript. A subscript is denoted by a ``['', followed by an arithmetic expression (see ``Arithmetic evaluation'') followed by a ``]''. To assign values to an array, use set -A name value ... . The value of all subscripts must be in the range 0 through 1023. Arrays need not be declared. Any reference to a named parameter with a valid subscript is legal and an array will be created if necessary. Referencing an array without a subscript is equivalent to referencing the element 0.

The value of a named parameter may also be assigned by writing:

name = value [ name[\1] = value[\1] ] ...

If the integer attribute, -i, is set for a given name the corresponding value is subject to arithmetic evaluation as described below.

Positional parameters, that is parameters denoted by a number, may be assigned values with the set special command. Parameter $0 is set from argument zero when the shell is invoked. The character ``$'' is used to introduce substitutable parameters.

${parameter}

The shell reads all the characters from ``${'' to the matching ``}'' as part of the same word even if it contains braces or metacharacters. The value, if any, of the parameter is substituted. The braces are required when parameter is followed by a letter, digit, or underscore that is not to be interpreted as part of its name or when a named parameter is subscripted. If parameter is one or more digits then it is a positional parameter. A positional parameter of more than one digit must be enclosed in braces. If parameter is ``'' or ``@'', then all the positional parameters, starting with $1, are substituted (separated by a field separator character). If an array identifier with subscript ``'' or ``@'' is used, then the value for each of the elements is substituted (separated by a field separator character).

${#parameter}

If parameter is ``'' or ``@'', the number of positional parameters is substituted. Otherwise, the length of the value of the parameter is substituted.

${#identifier[*]}

The number of elements in the array identifier is substituted.

${parameter:-word}

If parameter is set and is non-null then its value is substituted; otherwise word is substituted.

${parameter:=word}

If parameter is not set or is null then it is set to word; the value of the parameter is then substituted. Positional parameters may not be assigned to in this way.

${parameter:?word}

If parameter is set and is non-null then its value is substituted; otherwise, word is printed and the shell is exited. If word is omitted then a standard message is printed.

${parameter:+word}

If parameter is set and is non-null then word is substituted; otherwise nothing is substituted.

${parameter#pattern}
${parameter##pattern}

If the shell pattern matches the beginning of the value of parameter, then the value of this substitution is the value of the parameter with the matched portion deleted; otherwise the value of this parameter is substituted. In the first form the smallest matching pattern is deleted and in the second form the largest matching pattern is deleted.

${parameter%pattern}
${parameter%%pattern}

If the shell pattern matches the end of the value of parameter, then the value of this substitution is the value of the parameter with the matched part deleted; otherwise the value of parameter is substituted. In the first form the smallest matching pattern is deleted and in the second form the largest matching pattern is deleted.

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

The following parameters are automatically set by the shell:

#

The number of positional parameters in decimal.

-

Flags supplied to the shell on invocation or by the set command.

?

The decimal value returned by the last executed command.

$

The process number of this shell.

_

Initially, the absolute pathname of the shell or script being executed as passed in the environment. Subsequently it is assigned the last argument of the previous command. This parameter is not set for commands which are asynchronous. This parameter is also used to hold the name of the matching MAIL file when checking for mail.

!

The process number of the last background command invoked.

ERRNO

The value of errno as set by the most recent failed system call. This value is system dependent and is intended for debugging purposes.

LINENO

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

OLDPWD

The previous working directory set by the cd special command.

OPTARG

The value of the last option argument processed by the getopts special command.

OPTIND

The index of the last option argument processed by the getopts special command.

PPID

The process number of the parent of the shell.

PWD

The present working directory set by the cd command.

RANDOM

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

REPLY

This parameter is set by the select statement and by the read special command when no arguments are supplied.

SECONDS

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

CDPATH

The search path for the cd special command.

COLUMNS

If this variable is set, the value is used to define the width of the edit window for the shell edit modes and for printing select lists.

EDITOR

If the value of this variable ends in emacs, gmacs, or vi and the VISUAL variable is not set, then the corresponding option (see ``Special commands'') -- set is turned on.

ENV

If this parameter is set, then parameter substitution is performed on the value to generate the pathname of the script that is executed when the shell is invoked (see ``Invocation''). This file is typically used for alias and function definitions.

FCEDIT

The default editor name for the fc special command.

FPATH

The search path for function definitions. This path is searched when a function with the -u attribute is referenced but has not yet been defined. The shell searches for an executable file of the same name. If the file is found, it is sourced in: it should define the function, which is then executed. If the function is already defined, the function definition file is not searched for.

HISTFILE

If this parameter is set when the shell is invoked, then the value is the pathname of the file used to store the command history (see ``History file'').

HISTSIZE

If this parameter is set when the shell is invoked, then the number of previously entered commands that are accessible by this shell is greater than or equal to this number. The default is 128.

HOME

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

IFS

Internal field separators, normally space, tab, and newline, that are used to separate command words which result from command or parameter substitution, and for separating words with the special command read. The first character of the IFS parameter is used to separate arguments for the $ substitution. (See ``Quoting''.)

LINES

If this variable is set, the value is used to determine the column length for printing select lists. select lists print vertically until about two-thirds of LINES lines are filled.

MAIL

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

MAILCHECK

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

MAILPATH

A colon (:) separated list of filenames. If this parameter is set, then the shell informs the user of any modifications to the specified files that have occurred within the last MAILCHECK seconds. Each filename can be followed by a ``?'' and a message to be printed. The message undergoes parameter substitution with the parameter $_ defined as the name of the file that has changed. The default message is

you have mail in $_.

PATH

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

PS1

The value of this parameter is expanded for parameter substitution to define the primary prompt string which by default is ``$ '' (dollar-space). The character ``!'' in the primary prompt string is replaced by the command number (see ``History file'').

PS2

The secondary prompt string, by default ``> ''.

PS3

The selection prompt string used within a select loop, by default ``#? ''.

PS4

The value of this parameter is expanded for parameter substitution and precedes each line of an execution trace. If omitted, the execution trace prompt is ``+ ''.

SHELL

The pathname of the shell is kept in the environment. At invocation, if the basename of this variable matches the pattern *r*sh, then the shell becomes restricted.

TMOUT

If TMOUT is set to a value greater than 0, the shell terminates if a command is not entered within the prescribed number of seconds after issuing the PS1 prompt. (Note that the shell can be compiled with a maximum bound for this value which cannot be exceeded.)

VISUAL

If the value of this variable ends in emacs, gmacs, or vi, then the corresponding option (see ``Special commands'') is turned on.

Blank interpretation

Explicit null arguments ("" or '') are retained. Implicit null arguments (those resulting from parameters that have no values) are removed.

Filename generation

Quoting

$

$

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

Arithmetic evaluation

An arithmetic expression uses the syntax, precedence, and associativity of expression of the C language. All the integral operators, other than ++, --, ?:, and comma (,) are supported. Named parameters can be referenced by name within an arithmetic expression without using the parameter substitution syntax. When a named parameter is referenced, its value is evaluated as an arithmetic expression.

An internal integer representation of a named parameter can be specified with the -i option of the typeset special command. Arithmetic evaluation is performed on the value of each assignment to a named parameter with the -i attribute. If an arithmetic base is not specified, the first assignment to the parameter determines the arithmetic base. This base is used when parameter substitution occurs.

Since many of the arithmetic operators require quoting, an alternative form of the let command is provided. For any command which begins with a ((, all the characters until a matching )) are treated as a quoted expression. More precisely, ((...)) is equivalent to let "...".

Prompting

Conditional expressions

-a file

True, if file exists.

-b file

True, if file exists and is a block special file.

-c file

True, if file exists and is a character special file.

-d file

True, if file exists and is a directory.

-e file

True, if file exists.

-f file

True, if file exists and is an ordinary file.

-g file

True, if file exists and has its setgid bit set.

-G file

True, if file exists and its group matches the effective group ID of this process.

-H file

True, if file exists and is a semaphore.

-k file

True, if file exists and has its sticky bit set.

-L file

True, if file exists and is a symbolic link.

-M file

True, if file exists and is shared memory.

-n string

True, if the length of string is non-zero.

-o option

True, if the option named option is on.

-O file

True, if file exists and is owned by the effective user ID of this process.

-p file

True, if file exists and is a fifo special file or a pipe.

-r file

True, if file exists and is readable by the current process.

-s file

True, if file exists and has a size greater than zero.

-S file

True, if file exists and is a socket.

-t fildes

True, if file descriptor number fildes is open and associated with a terminal device.

-u file

True, if file exists and has its setuid bit set.

-w file

True, if file exists and is writable by the current process.

-x file

True, if file exists and is executable by the current process. If file exists and is a directory, then the current process has permission to search in the directory.

-z string

True, if the length of string is 0.

file1 -nt file2

True, if file1 exists and is newer than file2.

file1 -ot file2

True, if file1 exists and is older than file2.

file1 -ef file2

True, if file1 and file2 exist and refer to the same file.

string = pattern

True, if string matches pattern.

string != pattern

True, if string does not match pattern.

string1 < string2

True, if string1 comes before string2 based on the ASCII value of their characters.

string1 > string2

True, if string1 comes after string2 based on the ASCII value of their characters.

exp1 -eq exp2

True, if exp1 is equal to exp2.

exp1 -ne exp2

True, if exp1 is not equal to exp2.

exp1 -lt exp2

True, if exp1 is less than exp2.

exp1 -gt exp2

True, if exp1 is greater than exp2.

exp1 -le exp2

True, if exp1 is less than or equal to exp2.

exp1 -ge exp2

True, if exp1 is greater than or equal to exp2.

A compound expression can be constructed from these primitives by using any of the following, listed in decreasing order of precedence.

(expression)

True, if expression is true. This is used to group expressions.

! expression

True if expression is false.

expression1 && expression2

True, if expression1 and expression2 are both true.

expression1 || expression2

True, if either expression1 or expression2 is true.

Spelling checker

   /usr/spool/uucp? y
   ok

To disable the spelling checker, enter the following at the ksh prompt :

unset CDSPELL

When the user does a set at the ksh prompt, CDSPELL is not listed if the unset was successful.

Input/output

<word

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

>word

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

>|word

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

>>word

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

<>word

Open file word for reading and writing as standard input.

<<[-]word

Read the shell input up to a line that is the same as word, or to an end-of-file. No parameter substitution, command substitution or filename generation is performed on word. The resulting document, called a here-document, becomes the standard input. If any character of word is quoted, then no interpretation is placed upon the characters of the document; otherwise, parameter and command substitution occurs, \newline is ignored, and ``\'' must be used to quote the characters \, $, `, and the first character of word. If ``-'' is appended to <<, then all leading tabs are stripped from word and from the document.

<&digit

Duplicate the standard input from file descriptor digit (see dup(S)); similarly for the standard output using >&digit.

<&-

Close the standard input; similarly for the standard output using >&-.

<&p

Move the input from the co-process to standard input.

>&p

Move the output to the co-process to standard output.

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

File descriptor 0 is standard input; 1 is standard output; 2 is standard error.

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

... 1>fname 2>&1

first associates file descriptor 1 with file fname. It then associates file descriptor 2 with the file associated with file descriptor 1 (that is, fname). If the order of redirections were reversed, file descriptor 2 would be associated with the terminal (assuming this was the initial state of file descriptor 1) and then file descriptor 1 would be associated with file fname.

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

Environment

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

TERM=wy60 cmd args

and

(export TERM; TERM=wy60; cmd args)

are equivalent (as far as the above execution of cmd is concerned, except for commands listed with one or two daggers (+) in ``Special commands'').

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

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

Functions

Functions execute in the same process as the caller and share all files and the present working directory with the caller. Traps caught by the caller are reset to their default action inside the function. A trap condition that is not caught or ignored by the function causes the function to terminate and the condition to be passed on to the caller. A trap on EXIT set inside a function is executed after the function completes in the environment of the caller. Ordinarily, variables are shared between the calling program and the function. However, the typeset special command used within a function defines local variables whose scope includes the current function and all functions it calls.

The special command return is used to return from function calls. Errors within functions return control to the caller.

Function identifiers can be listed with the -f or +f option of the typeset special command. The text of functions are also listed with -f. Functions can be undefined with the -f option of the unset special command.

Ordinarily, functions are unset when the shell executes a shell script. The -xf option of the typeset command allows a function to be exported to scripts that are executed without a separate invocation of the shell. Functions that need to be defined across separate invocations of the shell should be specified in the ENV file with the -xf option of typeset.

Jobs

   [1] 1234

If you are running a job and wish to do something else you may hit the key ^Z (<Ctrl>Z) which sends a STOP signal to the current job. (This is known as the suspend character, and is ^Z by default; this can be changed in the stty susp line in a user's .profile file.) The shell then normally indicates that the job has been `Stopped', and prints another prompt. You can then manipulate the state of this job, putting it in the background with the bg command, or run some other commands and then eventually bring the job back into the foreground with the foreground command fg. A ^Z takes effect immediately and is like an interrupt in that pending output and unread input are discarded when it is typed.

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

There are several ways to refer to jobs in the shell. A job can be referred to by the process ID of any process of the job or by one of the following:

%number

The job with the given number.

%string

Any job whose command line begins with string.

%?string

Any job whose command line contains string.

%%

%+

The current job.

%-

The previous job.

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

When you try to leave the shell while jobs are running or stopped, you will be warned that ``You have stopped(running) jobs.'' You may use the jobs command to see what they are. If you do this or immediately try to exit again, the shell will not warn you a second time, and the stopped jobs will be terminated.

Signals

Execution

The shell parameter PATH defines the search path for the directory containing the command. Alternative directory names are separated by a colon (:). The default path is /bin:/usr/bin: (specifying /bin, /usr/bin, and the current directory in that order). The current directory can be specified by two or more adjacent colons, or by a colon at the beginning or end of the path list. If the command name contains a ``/'' then the search path is not used. Otherwise, each directory in the path is searched for an executable file. If the file has execute permission but is not a directory or an a.out file, it is assumed to be a file containing shell commands. A sub-shell is spawned to read it. In this case, all non-exported aliases, functions, and named parameters are removed. If the shell command file does not have read permission, or if the setuid and/or setgid bits are set on the file, then the shell executes an agent whose job is to set up the permissions and execute the shell with the shell command file passed down as an open file. A parenthesized command is executed in a sub-shell without removing non-exported quantities.

Special commands

1. Parameter assignment lists preceding the command remain in effect when the command completes.

2. I/O redirections are processed after parameter assignments.

3. Errors cause a script that contains them to abort.

4. Words, following a command preceded by ++ that are in the format of a parameter assignment, are expanded with the same rules as a parameter assignment. This means that tilde substitution is performed after the ``='' sign and that word splitting and filename generation are not performed.

+ : [ arg ... ]

Expand parameters.

+ . file [ arg ... ]

Read the complete file then execute the commands. The syntax for this is dot-space-file followed by optional arguments. The commands are executed in the current shell environment. The search path specified by PATH is used to find the directory containing file. If any arguments arg are given, they become the positional parameters. Otherwise the positional parameters are unchanged. The exit status is the exit status of the last command executed.

++ alias [ -tx ] [ name [ = value ] ] ...

With no arguments, print the list of aliases in the form name=value on standard output. An alias is defined for each name whose value is given. A trailing space in value causes the next word to be checked for alias substitution.

The -t flag is used to set and list tracked aliases. The value of a tracked alias is the full pathname corresponding to the given name. The value becomes undefined when the value of PATH is reset but the aliases remained tracked. Without the -t flag, for each name in the argument list for which no value is given, the name and value of the alias is printed.

The -x flag is used to set or print exported aliases. An exported alias is defined for scripts invoked by name. The exit status is non-zero if a name is given, but no value, for which no alias has been defined.

See also alias(C).

bg [ job ... ]

Run jobs in the background. This command only works if job control is enabled. It puts each specified job into the background. The current job is put in the background if job is not specified. See ``Jobs'' for a description of the format of job.

See also bg(C).

+ break [ n ]

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

+ continue [ n ]

Resume the next iteration of the enclosing for, while, until, or select loop. If n is specified then resume at the nth enclosing loop.

cd [ -L | -P ] [ arg ]
cd [ -L | -P ] old new

If the first form, change the current directory to arg and set the parameter PWD to the current directory.

If arg is ``-'', the directory is changed to the previous directory (taken from the value of the shell parameter OLDPWD).

If no arg is specified, the shell parameter HOME is used as a default arg.

The shell parameter CDPATH defines the search path for the directory containing arg. Alternative directory names are separated by a colon ``:''. The default path is <null> (specifying the current directory). Note that the current directory is specified by a null pathname, which can appear immediately after the equal sign or between the colon delimiters anywhere else in the path list. If arg begins with a ``/'' then the search path is not used. Otherwise, each directory in the path is searched for arg.

The second form of cd substitutes the string new for the string old in the current directory name, PWD, and tries to change to the new directory formed.

The -L and -P flags are relevant to systems with symbolic links:

-L

Preserve logical pathnames so that cd -L .. moves up one component towards the root along the current logical path. This is the default behavior.

-P

Use a physical model for pathnames so that cd -L .. moves up one component towards the root by following the link to the parent of the current directory.

 

For example, if /usr/include/sys/h is a symbolic link to the directory /sys/h, then cd /usr/include/sys/h; cd .. or cd /usr/include/sys/h; cd -L .. would make /usr/include/sys the current directory; cd /usr/include/sys/h; cd -P .. would make /sys the current directory.

The cd command may not be executed by rksh.

See also cd(C).

command [ -p ] name [ argument ... ]
command [ -v | -V ] name

Execute a command without invoking a user-defined function, or prevent an error in a built-in command aborting the shell. See command(C) for usage and description.

echo [ arg ... ]

Write arguments to the standard output.

NOTE: /bin/posix/sh, linked to ksh, supplies the functionality for echo as defined by ISO/IEC DIS 99452:1992, Information technology Portable Operating System Interface (POSIX) Part 2: Shell and Utilities (IEEE Std 1003.21992) and X/Open CAE Specification, Commands and Utilities, Issue 4, 1992.

See echo(C) for usage and description.

+ eval [ arg ... ]

Read the arguments as input to the shell and execute the resulting command(s).

+ exec [ arg ... ]

If arg is given, execute the command specified by the arguments in place of this shell without creating a new process. Input/output arguments may appear and affect the current process. If no arguments are given, the effect of this command is to modify file descriptors as prescribed by the input/output redirection list. In this case, any file descriptor numbers greater than 2 that are opened with this mechanism are closed when invoking another program.

+ exit [ n ]

Cause the shell to exit with the exit status specified by n. If n is omitted then the exit status is that of the last command executed. An end-of-file will also cause the shell to exit except for a shell which has the ignoreeof option (see ``set'' below) turned on.

++ export [ -p ] [ name [ = value ] ] ...

Mark the given names for automatic export to the environment of subsequently executed commands. The -p flag, if present, causes currently exported names to be listed on the standard output.

false

Always return a non-zero value. See also false(C).

fc [ -e ename  ] [ -nlr ] [ first [ last ] ]

fc -s [ old\=new ] [ command ]

fc -e - [ old\=new ] [ command ]

In the first form, select a range of commands from first to last from the last HISTSIZE commands that were typed at the terminal. The arguments first and last may be specified as a number or as a string. A string is used to locate the most recent command that starts with that string. A negative number is used as an offset to the current command number.

 

-l lists commands on standard output. Otherwise, the editor program ename is invoked on a file containing these keyboard commands. If ename is not supplied, then the value of the parameter FCEDIT (default /bin/ed) is used as the editor. When editing is complete, the edited command(s) is executed. If last is not specified then it is set to first. If first is not specified the default is the previous command for editing and -l6 for listing.

-n suppresses command numbers when listing.

-r reverses the order of the commands when listing.

In the second and third forms, the command is re-executed after the substitution old=new is performed.

See also fc(C).

fg [ job ... ]

Run jobs in the foreground. This command only works if job control is enabled. Each job specified is brought to the foreground. Otherwise, the current job is brought into the foreground. See ``Jobs'' for a description of the format of job.

See also fg(C).

getopts optstring name [ arg ... ]

Check arg for legal options. If arg is omitted, the positional parameters are used. An option argument begins with a ``+'' or a ``-''. An option not beginning with ``+'' or ``-'' or the special argument ``--'' ends the options. optstring contains the letters that getopts recognizes. If a letter is followed by a ``:'', that option is expected to have an argument. The options can be separated from the argument by blanks.

getopts places the next option letter it finds inside variable name each time it is invoked with a ``+'' prefixed when arg begins with a ``+''. The index of the next arg is stored in OPTIND. The option argument, if any, is stored in OPTARG.

A leading ``:'' in optstring causes getopts to store the letter of an invalid option in OPTARG, and to set name to ``?'' for an unknown option and to ``:'' when a required option is missing. Otherwise, getopts prints an error message. The exit status is non-zero when there are no more options. See also getopts(C).

hash [ utility ... ]
hash -r

Remember, report, or forget locations of commands. See hash(C) for usage and description.

jobs [ -l | -p ] [ -n ] [ job ... ]

List information about each given job, or all active jobs if job is omitted. See ``Jobs'' for a description of the format of job.

jobs accepts the following options:

-l

List process IDs in addition to the normal information.

-n

List only jobs that have stopped or exited since last notified.

-p

List only the process group.

See also jobs(C).

kill [ -sig ] [ -s signame ] job ...
kill -l [ exit_status ]

Send either the TERM (terminate) signal or the specified signal to the specified jobs or processes. Signals are either given by number or by names (as given in /usr/include/signal.h, stripped of the prefix SIG). If the signal being sent is TERM (terminate) or HUP (hangup), then the job or process will be sent a CONT (continue) signal if it is stopped. The argument job can specify the process ID of a process that is not a member of one of the active jobs. See ``Jobs'' for a description of the format of job.

In the second form, kill -l, the signal names are listed. If an exit_status is given, the signal name corresponding to the status is output.

See kill(C) for a full description of this command.

let arg ...

Each arg is a separate arithmetic expression to be evaluated. See ``Arithmetic evaluation'' for a description of arithmetic expression evaluation.

The exit status is 0 if the value of the last expression is non-zero, and 1 otherwise.

newgrp [ - | -l ] [ group ... ]

Set a new real and effective group ID. This is equivalent to exec /bin/newgrp. See newgrp(C) for a full description of this command.

print [ -Rnprs ] [ -u [n ] ] [ arg ... ]

The shell output mechanism. With no flags or with flag ``-'' or ``--'' the arguments are printed on standard output as described in echo(C). In raw mode, -R or -r, the escape conventions of echo are ignored. The -R option prints all subsequent arguments and options other than -n. The -p option causes the arguments to be written onto the pipe of the process spawned with |& instead of standard output. The -s option causes the arguments to be written onto the history file instead of standard output. The -u flag can be used to specify a one-digit file descriptor unit number n on which the output is placed. The default is 1. If the flag -n is used, no newline is added to the output.

pwd [ -L | -P ]

Print the pathname of the current working directory. This is equivalent to print -r - $PWD .

The -L and -P flags are relevant only on systems with symbolic links:

-L

Show the logical pathname to the directory preserving the route taken to get there. This is the default behavior.

-P

Show the physical pathname to the directory.

 

For example, if /usr/include/sys/h is a symbolic link to the directory /sys/h, then cd /usr/include/sys/h; pwd or cd /usr/include/sys/h; pwd -L prints /usr/include/sys/h as the current working directory; cd/usr/include/sys/h; pwd -P prints /sys/h as the current working directory.

See also pwd(C).

read [ -prs ] [ -u [ n ] ] [ name?prompt ] [ name ... ]

The shell input mechanism. One line is read and is broken up into fields using the characters in IFS as separators.

The first field is assigned to the first name, the second field to the second name, and so on, with leftover fields assigned to the last name.

read accepts the following options:

-p

Take the input line from the input pipe of a process spawned by the shell using |&. An end-of-file with this option causes cleanup for this process so that another can be spawned.

-r

A ``\'' at the end of a line does not signify line continuation.

-s

Save the input as a command in the history file.

-u n

Specify a one-digit file descriptor n to read from. The file descriptor can be opened with the exec special command. The default value of n is 0.

 

If name is omitted then REPLY is used as the default name. If the first name argument contains a ``?'', the remainder of this word (beyond ``?'') is used as a prompt on standard error when the shell is interactive.

The exit status is 0 unless an end-of-file is encountered.

++ readonly [ -p ] [ name [ = value ] ] ...

Mark the given names read-only; these names cannot be changed by subsequent assignment. If the -p option is specified, current read-only names are listed on the standard output.

+ return [ n ]

Return a shell function to the invoking script with the return status specified by n. If n is omitted then the return status is that of the last command executed. If return is invoked while not in a function or a ``.'' script, then it is the same as an exit.

set [ ±aefhkmnopstuvx ] [ ±o option ]... [ ±A name ] [ arg ... ]

Perform the following functions:

• With no options or arguments, list the variables set in the current shell together with their values.

• Override the positional parameters for the current shell. For example, set $(date) sets the positional parameters $1, $2, ... to the output from the date command.

• Redefine the behavior of the current shell.

set takes the following options:

-A

Array assignment. Unset the variable name and assign values sequentially from the list arg. If +A is used, the variable name is not unset first.

-a

Automatically export all subsequent parameters that are defined.

-e

If a command has a non-zero exit status, execute the ERR trap, if set, and exit. This mode is disabled while reading profiles.

-f

Disable filename generation.

-h

Cause each command to become a tracked alias when first encountered.

-k

Place all parameter assignment arguments in the environment for a command, not just those that precede the command name.

-m

Run background jobs in a separate process group and print a line upon completion. The exit status of background jobs is reported in a completion message. This flag is turned on automatically for interactive shells.

-n

Read commands and check them for syntax errors, but do not execute them. This is ignored for interactive shells.

-o

List all option settings.

The argument following -o can be one of the following option names:

allexport

Same as -a.

errexit

Same as -e.

bgnice

Run all background jobs at a lower priority. This is the default mode.

emacs

Switch to an emacs style in-line editor for command entry.

gmacs

Switch to a gmacs style in-line editor for command entry.

ignoreeof

Do not exit the shell on end-of-file. The command exit must be used.

keyword

Same as -k.

markdirs

Append all directory names resulting from filename generation with a trailing ``/''.

monitor

Same as -m.

noclobber

Prevent output redirection (>) from truncating existing files. Enforce >| to truncate a file when turned on.

noexec

Same as -n.

noglob

Same as -f.

nolog

Do not save function definitions in the history file.

nounset

Same as -u.

privileged

Same as -p.

trackall

Same as -h.

verbose

Same as -v.

vi

Switch to insert mode of a vi style in-line editor escape character until 033 is entered. This switches to move mode. <Enter> sends the line.

viraw

Process each character as it is typed in vi mode.

xtrace

Same as -x.

-p

Disable processing of the $HOME/.profile file and use the file /etc/suid_profile instead of the ENV file. This mode is on whenever the effective user ID (group ID) is not equal to the real user ID (group ID). Turning this off causes the effective user ID and group ID to be set to the real user ID and group ID.

-s

Sort the positional parameters lexicographically.

-t

Exit after reading and executing one command.

-u

Treat unset parameters as an error when substituting.

-v

Print shell input lines as they are read.

-x

Print commands and their arguments as they are executed.

-

Turn off -x and -v flags and stop examining arguments for flags.

--

Do not change any of the flags; this is useful in setting $1 to a value beginning with ``-''. If no arguments follow this flag then the positional parameters are unset.

Using ``+'' rather than ``-'' causes these flags to be turned off. These flags can also be used upon invocation of the shell. The current set of flags may be found in $-. Unless -A is specified, the remaining arguments are positional parameters and are assigned, in order, to $1 $2 .... If no arguments are given then the names and values of all named parameters are printed on the standard output. If the only argument is ``+'', the names of all named parameters are printed.

+ shift [ n ]

Rename the positional parameters from $n+1 ... to 1 ..., where the default n is 1. The parameter n can be any arithmetic expression that evaluates to a non-negative number less than or equal to $#.

test expr

[ expr ]

Evaluate an expression as being true or false. This built-in command is equivalent to /bin/test. It differs slightly from conditional expressions of the form [[ expr ]].

See the section ``Conditional expressions'' and test(C).

+ times

Print the accumulated user and system times for the shell and for processes run from the shell.

+ trap [ arg ] [ sig ] ...

arg is a command to be read and executed when the shell receives signal(s) sig. (Note that arg is scanned once when the trap is set and once when the trap is taken.) Each sig can be given as a number or as the name of the signal (see the description of kill or kill(C)). Trap commands are executed in order of signal number. Any attempt to set a trap on a signal that was ignored on entry to the current shell is ineffective.

If arg is omitted or is ``-'', then all trap signals are reset to their original values.

If arg is the null string then this signal is ignored by the shell and by the commands it invokes.

If sig is ERR then arg is executed whenever a command has a non-zero exit status.

If sig is DEBUG then arg is executed after each command.

If sig is 0 or EXIT and the trap statement is executed inside the body of a function, then the command arg is executed after the function completes.

If sig is 0 or EXIT for a trap set outside any function, then the command arg is executed on exit from the shell.

Entering trap with no arguments prints a list of commands associated with each signal number.

true

Always return 0. See also true(C).

type command ...

Determine command type. See type(C) for usage and description.

++ typeset [ ±HLRZfilrtux[n] ] [ name[ =value ] ] ...

Set attributes and values for shell parameters. When invoked inside a function, a new instance of the parameter name is created. The parameter value and type are restored when the function completes. The following list of attributes may be specified:

-H

Provide UNIX system to host-name file mapping on non-UNIX system machines.

-L

Left justify and remove leading blanks from value. If n is non-zero it defines the width of the field; otherwise it is determined by the width of the value of first assignment. When the parameter is assigned to, it is filled on the right with blanks or truncated, if necessary, to fit into the field. Leading zeros are removed if the -Z flag is also set. The -R flag is turned off.

-R

Right justify and fill with leading blanks. If n is non-zero it defines the width of the field; otherwise it is determined by the width of the value of first assignment. The field is left-filled with blanks or truncated from the end if the parameter is reassigned. The -L flag is turned off.

-Z

Right justify and fill with leading zeros if the first non-blank character is a digit and the -L flag has not been set. If n is non-zero it defines the width of the field; otherwise it is determined by the width of the value of first assignment.

-f

Cause names to refer to function names rather than parameter names. No assignments can be made and the only other valid flags are -t, -u and -x. The flag -t turns on execution tracing for this function. The flag -u causes this function to be marked as undefined. The FPATH variable is searched to find the function definition when the function is referenced. The flag -x allows the function definition to remain in effect across shell procedures invoked by name.

-i

Declare the parameter to be an integer. This makes arithmetic faster. If n is non-zero it defines the output arithmetic base; otherwise the first assignment determines the output base.

-l

Convert all uppercase characters to lowercase. The uppercase flag, -u, is turned off.

-r

Mark the given names read-only; these names cannot be changed by subsequent assignment.

-t

Tag the named parameters. Tags are user definable and have no special meaning to the shell.

-u

Convert all lowercase characters to uppercase characters. The lowercase flag, -l, is turned off.

-x

Mark the given names for automatic export to the environment of subsequently-executed commands.

 

Using ``+'' rather than ``-'' causes these flags to be turned off. If no name arguments are given but flags are specified, a list of names (and optionally the values) of the parameters which have these flags set is printed. (Using ``+'' rather than ``-'' keeps the values from being printed.) If no names and flags are given, the names and attributes of all parameters are printed.

ulimit [ -acdfnstvHS ] [ limit ]

Set or display a resource limit. If a limit is provided, then the resource limit is set. The list of available resources is given below. The limit argument should be either a number or the word ``unlimited''. The -H flag sets the hard limit and the -S flag sets the soft limit. If neither -H nor -S is specified, both the hard and soft limits will be set. The hard limit cannot be raised, but the soft limit can be set to any value up to the hard limit.

 

If no limit is provided, the current limit is printed. The soft limit is printed unless the -H flag is specified. If more than one resource limit is printed, a description of each resource is printed before the limit.

 

If no resource is specified when setting or displaying limits, the -f flag is assumed.

The following flags are recognized:

-a

List all the current resource limits.

-c

Size of core files (in 512-byte blocks).

-d

Size of data region (in KB).

-f

Size of files created (in 512-byte blocks).

-n

Number of open file descriptors.

-s

Size of process's stack (in KB).

-t

Number of seconds used by each process.

-v

Size of a process's virtual address space (in KB).

See also ulimit(C).

umask [ -S ] [ mask ]

Get or set the file-creation mode mask. See umask(C) for usage and description.

unalias name ...

unalias -a

In the first form of the command, remove the parameters given by the list of names from the alias list. The second form removes all aliases from the list. See also the description of unalias on the alias(C) manual page.

unset [ -f ] name ...

Unassign the parameters given by the list of names, that is, erase their values and attributes. readonly variables cannot be unset. If the flag -f is set, then the names refer to function names. Unsetting ERRNO, LINENO, MAILCHECK, OPTARG, OPTIND, RANDOM, SECONDS, TMOUT, and ``_'' removes their special meaning even if they are subsequently assigned to.

+ wait [ job ]

Wait for the specified job and report its termination status. If job is not given then all currently active child processes are waited for. The exit status from this command is that of the process waited for. See ``Jobs'' for a description of the format of job.

See also wait(C).

whence [ -pv ] name ...

For each name, indicate how it would be interpreted if used as a command name.

whence accepts the following options:

-v

Produce a more verbose report.

-p

Do a path search for name even if name is an alias, a function, or a reserved word.

Invocation

-c string

If the -c flag is present then commands are read from string.

-s

If the -s flag is present or if no arguments remain then commands are read from the standard input. Shell output, except for the output of the special commands listed above, is written to file descriptor 2.

-i

If the -i flag is present or if the shell input and output are attached to a terminal (as told by ioctl(S)) then this shell is interactive. In this case TERM is ignored (so that kill 0 does not kill an interactive shell) and INTR is caught and ignored (so that wait is interruptible). In all cases, QUIT is ignored by the shell.

-r

If the -r flag is present the shell is a restricted shell.

rksh only

• changing directory (see cd(C))

• setting the value of SHELL, ENV, or PATH

• specifying path or command names containing ``/''

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

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

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

The system administrator often sets up a directory of commands (for example, /usr/rbin) that can be safely invoked by rksh. There is also a restricted editor, red.

Note that simply setting a user's login shell to rksh does not make their account ``safe''. Some thought and care must be put into creating a properly restricted environment.

Diagnostics

Examples

Limitations

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

Using the fc built-in command within a compound command causes the whole command to disappear from the history file.

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

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

Files

/tmp/sh

Open UNIX 8 compatibility notes

See also

Chapter 10, ``Configuring and working with the shells'' in the &osr Operating System User's Guide

The KornShell Command and Programming Language, by Morris I. Bolsky and David G. Korn, Prentice Hall, 1989.

Standards conformance

ISO/IEC DIS 99452:1992, Information technology Portable Operating System Interface (POSIX) Part 2: Shell and Utilities (IEEE Std 1003.21992);
AT&T SVID Issue 2;
X/Open CAE Specification, Commands and Utilities, Issue 4, 1992.