KSH(1) User commands KSH(1)
NAME
ksh - Public domain Korn shell
SYNOPSIS
ksh [?abCefhikmnprsuvxX] [?o option] [ [ -c command-string [command-name] | -s | file ]
[argument ...] ]
DESCRIPTION
ksh is a command interpreter that is intended for both interactive and shell script use.
Its command language is a superset of the sh(1) shell language.
Shell Startup
The following options can be specified only on the command line:
-c command-string
the shell executes the command(s) contained in command-string
-i interactive mode -- see below
-l login shell -- see below interactive mode -- see below
-s the shell reads commands from standard input; all non-option arguments are posi-
tional parameters
-r restricted mode -- see below
In addition to the above, the options described in the set built-in command can also be
used on the command line.
If neither the -c nor the -s options are specified, the first non-option argument speci-
fies the name of a file the shell reads commands from; if there are no non-option argu-
ments, the shell reads commands from standard input. The name of the shell (i.e., the
contents of the $0) parameter is determined as follows: if the -c option is used and there
is a non-option argument, it is used as the name; if commands are being read from a file,
the file is used as the name; otherwise the name the shell was called with (i.e., argv[0])
is used.
A shell is interactive if the -i option is used or if both standard input and standard
error are attached to a tty. An interactive shell has job control enabled (if available),
ignores the INT, QUIT and TERM signals, and prints prompts before reading input (see PS1
and PS2 parameters). For non-interactive shells, the trackall option is on by default
(see set command below).
A shell is restricted if the -r option is used or if either the basename of the name the
shell is invoked with or the SHELL parameter match the pattern *r*sh (e.g., rsh, rksh,
rpdksh, etc.). The following restrictions come into effect after the shell processes any
profile and $ENV files:
? the cd command is disabled
? the SHELL, ENV and PATH parameters can't be changed
? command names can't be specified with absolute or relative paths
? the -p option of the command built-in can't be used
? redirections that create files can't be used (i.e., >, >|, >>, <>)
A shell is privileged if the -p option is used or if the real user-id or group-id does not
match the effective user-id or group-id (see getuid(2), getgid(2)). A privileged shell
does not process $HOME/.profile nor the ENV parameter (see below), instead the file
/etc/suid_profile is processed. Clearing the privileged option causes the shell to set
its effective user-id (group-id) to its real user-id (group-id).
If the basename of the name the shell is called with (i.e., argv[0]) starts with - or if
the -l option is used, the shell is assumed to be a login shell and the shell reads and
executes the contents of /etc/profile and $HOME/.profile if they exist and are readable.
If the ENV parameter is set when the shell starts (or, in the case of login shells, after
any profiles are processed), its value is subjected to parameter, command, arithmetic and
tilde substitution and the resulting file (if any) is read and executed. If ENV parameter
is not set (and not null) and pdksh was compiled with the DEFAULT_ENV macro defined, the
file named in that macro is included (after the above mentioned substitutions have been
performed).
The exit status of the shell is 127 if the command file specified on the command line
could not be opened, or non-zero if a fatal syntax error occurred during the execution of
a script. In the absence of fatal errors, the exit status is that of the last command
executed, or zero, if no command is executed.
Command Syntax
The shell begins parsing its input by breaking it into words. Words, which are sequences
of characters, are delimited by unquoted white-space characters (space, tab and newline)
or meta-characters (<, >, |, ;, &, ( and )). Aside from delimiting words, spaces and tabs
are ignored, while newlines usually delimit commands. The meta-characters are used in
building the following tokens: <, <&, <<, >, >&, >>, etc. are used to specify redirections
(see Input/Output Redirection below); | is used to create pipelines; |& is used to create
co-processes (see Co-Processes below); ; is used to separate commands; & is used to create
asynchronous pipelines; && and || are used to specify conditional execution; ;; is used in
case statements; (( .. )) are used in arithmetic expressions; and lastly, ( .. ) are used
to create subshells.
White-space and meta-characters can be quoted individually using backslash (\), or in
groups using double (") or single (') quotes. Note that the following characters are also
treated specially by the shell and must be quoted if they are to represent themselves: \,
", ', #, $, ', ~, {, }, *, ? and [. The first three of these are the above mentioned
quoting characters (see Quoting below); #, if used at the beginning of a word, introduces
a comment -- everything after the # up to the nearest newline is ignored; $ is used to
introduce parameter, command and arithmetic substitutions (see Substitution below); '
introduces an old-style command substitution (see Substitution below); ~ begins a direc-
tory expansion (see Tilde Expansion below); { and } delimit csh(1) style alternations (see
Brace Expansion below); and, finally, *, ? and [ are used in file name generation (see
File Name Patterns below).
As words and tokens are parsed, the shell builds commands, of which there are two basic
types: simple-commands, typically programs that are executed, and compound-commands, such
as for and if statements, grouping constructs and function definitions.
A simple-command consists of some combination of parameter assignments (see Parameters
below), input/output redirections (see Input/Output Redirections below), and command
words; the only restriction is that parameter assignments come before any command words.
The command words, if any, define the command that is to be executed and its arguments.
The command may be a shell built-in command, a function or an external command, i.e., a
separate executable file that is located using the PATH parameter (see Command Execution
below). Note that all command constructs have an exit status: for external commands, this
is related to the status returned by wait(2) (if the command could not be found, the exit
status is 127, if it could not be executed, the exit status is 126); the exit status of
other command constructs (built-in commands, functions, compound-commands, pipelines,
lists, etc.) are all well defined and are described where the construct is described. The
exit status of a command consisting only of parameter assignments is that of the last com-
mand substitution performed during the parameter assignment or zero if there were no com-
mand substitutions.
Commands can be chained together using the | token to form pipelines, in which the stan-
dard 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 sta-
tus will be 1, and if the original status was not 0, then the complemented status will be
0.
Lists of commands can be created by separating pipelines by any of the following tokens:
&&, ||, &, |& and ;. The first two are for conditional execution: cmd1 && cmd2 executes
cmd2 only if the exit status of cmd1 is zero; || is the opposite -- cmd2 is executed only
if the exit status of cmd1 is non-zero. && and || have equal precedence which is higher
than that of &, |& and ;, which also have equal precedence. The & token causes the pre-
ceding 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 con-
trol is disabled (i.e., in most scripts), the command is started with signals INT and QUIT
ignored and with input redirected from /dev/null (however, redirections specified in the
asynchronous command have precedence). The |& operator starts a co-process which is spe-
cial kind of asynchronous process (see Co-Processes below). Note that a command must fol-
low the && and || operators, while a command need not follow &, |& and ;. The exit status
of a list is that of the last command executed, with the exception of asynchronous lists,
for which the exit status is 0.
Compound commands are created using the following reserved words -- these words are only
recognized if they are unquoted and if they are used as the first word of a command (i.e.,
they can't be preceded by parameter assignments or redirections):
case else function then !
do esac if time [[
done fi in until {
elif for select while }
Note: Some shells (but not this one) execute control structure commands in a subshell when
one or more of their file descriptors are redirected, so any environment changes inside
them may fail. To be portable, the exec statement should be used instead to redirect file
descriptors before the control structure.
In the following compound command descriptions, command lists (denoted as list) that are
followed by reserved words must end with a semi-colon, a newline or a (syntactically cor-
rect) reserved word. For example,
{ echo foo; echo bar; }
{ echo foo; echo bar}
{ { echo foo; echo bar; } }
are all valid, but
{ echo foo; echo bar }
is not.
( list )
Execute list in a subshell. There is no implicit way to pass environment changes
from a subshell back to its parent.
{ list }
Compound construct; list is executed, but not in a subshell. Note that { and } are
reserved words, not meta-characters.
case word in [ [(] pattern [| pattern] ... ) list ;; ] ... esac
The case statement attempts to match word against the specified patterns; the list
associated with the first successfully matched pattern is executed. Patterns used
in case statements are the same as those used for file name patterns except that
the restrictions regarding . and / are dropped. Note that any unquoted space
before and after a pattern is stripped; any space with a pattern must be quoted.
Both the word and the patterns are subject to parameter, command, and arithmetic
substitution as well as tilde substitution. For historical reasons, open and close
braces may be used instead of in and esac (e.g., case $foo { *) echo bar; }). The
exit status of a case statement is that of the executed list; if no list is exe-
cuted, the exit status is zero.
for name [ in word ... term ] do list done
where term is either a newline or a ;. For each word in the specified word list,
the parameter name is set to the word and list is executed. If in is not used to
specify a word list, the positional parameters ("$1", "$2", etc.) are used instead.
For historical reasons, open and close braces may be used instead of do and done
(e.g., for i; { echo $i; }). The exit status of a for statement is the last exit
status of list; if list is never executed, the exit status is zero.
if list then list [elif list then list] ... [else list] fi
If the exit status of the first list is zero, the second list is executed; other-
wise 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 exe-
cuted, the exit status is zero.
select name [ in word ... term ] do list done
where term is either a newline or a ;. The select statement provides an automatic
method of presenting the user with a menu and selecting from it. An enumerated
list of the specified words is printed on standard error, followed by a prompt
(PS3, normally '#? '). A number corresponding to one of the enumerated words is
then read from standard input, name is set to the selected word (or is unset if the
selection is not valid), REPLY is set to what was read (leading/trailing space is
stripped), and list is executed. If a blank line (i.e., zero or more IFS charac-
ters) is entered, the menu is re-printed without executing list. When list com-
pletes, the enumerated list is printed if REPLY is null, the prompt is printed and
so on. This process is continues until an end-of-file is read, an interrupt is
received or a break statement is executed inside the loop. If in word ... is omit-
ted, the positional parameters are used (i.e., "$1", "$2", etc.). For historical
reasons, open and close braces may be used instead of do and done (e.g., select i;
{ echo $i; }). The exit status of a select statement is zero if a break statement
is used to exit the loop, non-zero otherwise.
until list do list done
This works like while, except that the body is executed only while the exit status
of the first list is non-zero.
while list do list done
A while is a prechecked loop. Its body is executed as often as the exit status of
the first list is zero. The exit status of a while statement is the last exit sta-
tus of the list in the body of the loop; if the body is not executed, the exit sta-
tus is zero.
function name { list }
Defines the function name. See Functions below. Note that redirections specified
after a function definition are performed whenever the function is executed, not
when the function definition is executed.
name () command
Mostly the same as function. See Functions below.
time [ -p ] [ pipeline ]
The time reserved word is described in the Command Execution section.
(( expression ))
The arithmetic expression expression is evaluated; equivalent to let "expression".
See Arithmetic Expressions and the let command below.
[[ expression ]]
Similar to the test and [ ... ] commands (described later), with the following
exceptions:
? Field splitting and file name generation are not performed on arguments.
? The -a (and) and -o (or) operators are replaced with && and ||, respec-
tively.
? Operators (e.g., -f, =, !, etc.) must be unquoted.
? The second operand of != and = expressions are patterns (e.g., the compari-
son in
[[ foobar = f*r ]]
succeeds).
? There are two additional binary operators: < and > which return true if
their first string operand is less than, or greater than, their second
string operand, respectively.
? The single argument form of test, which tests if the argument has non-zero
length, is not valid - explicit operators must be always be used, e.g.,
instead of
[ str ]
use
[[ -n str ]]
? Parameter, command and arithmetic substitutions are performed as expressions
are evaluated and lazy expression evaluation is used for the && and ||
operators. This means that in the statement
[[ -r foo && $(< foo) = b*r ]]
the $(< foo) is evaluated if and only if the file foo exists and is read-
able.
Quoting
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 dou-
ble-quoted substitutions. If a \ inside a double-quoted string is followed by \, $, ' or
", it is replaced by the second character; if it is followed by a newline, both the \ and
the newline are stripped; otherwise, both the \ and the character following are unchanged.
Note: see POSIX Mode below for a special rule regarding sequences of the form
"...'...\"...'..".
Aliases
There are two types of aliases: normal command aliases and tracked aliases. Command
aliases are normally used as a short hand for a long or often used command. The shell
expands command aliases (i.e., substitutes the alias name for its value) when it reads the
first word of a command. An expanded alias is re-processed to check for more aliases. If
a command alias ends in a space or tab, the following word is also checked for alias
expansion. The alias expansion process stops when a word that is not an alias is found,
when a quoted word is found or when an alias word that is currently being expanded is
found.
The following command aliases are defined automatically by the shell:
autoload='typeset -fu'
functions='typeset -f'
hash='alias -t'
history='fc -l'
integer='typeset -i'
local='typeset'
login='exec login'
newgrp='exec newgrp'
nohup='nohup '
r='fc -e -'
stop='kill -STOP'
suspend='kill -STOP $$'
type='whence -v'
Tracked aliases allow the shell to remember where it found a particular command. The
first time the shell does a path search for a command that is marked as a tracked alias,
it saves the full path of the command. The next time the command is executed, the shell
checks the saved path to see that it is still valid, and if so, avoids repeating the path
search. Tracked aliases can be listed and created using alias -t. Note that changing the
PATH parameter clears the saved paths for all tracked aliases. If the trackall option is
set (i.e., set -o trackall or set -h), the shell tracks all commands. This option is set
automatically for non-interactive shells. For interactive shells, only the following com-
mands are automatically tracked: cat, cc, chmod, cp, date, ed, emacs, grep, ls, mail,
make, mv, pr, rm, sed, sh, vi and who.
Substitution
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 sec-
tion, take the form $name or ${...}; command substitutions take the form $(command) or
'command'; and arithmetic substitutions take the form $((expression)).
If a substitution appears outside of double quotes, the results of the substitution are
generally subject to word or field splitting according to the current value of the IFS
parameter. The IFS parameter specifies a list of characters which are used to break a
string up into several words; any characters from the set space, tab and newline that
appear in the IFS characters are called IFS white space. Sequences of one or more IFS
white space characters, in combination with zero or one non-IFS white space characters
delimit a field. As a special case, leading and trailing IFS white space is stripped
(i.e., no leading or trailing empty field is created by it); leading or trailing non-IFS
white space does create an empty field. Example: if IFS is set to ':', the
sequence of characters 'A:B::D' contains four fields: 'A',
'B', '' and 'D'. Note that if the IFS parameter is set to the null string, no field
splitting is done; if the parameter is unset, the default value of space, tab and newline
is used.
The results of substitution are, unless otherwise specified, also subject to brace expan-
sion and file name expansion (see the relevant sections 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 $, ' or \ is
stripped (a \ followed by any other character is unchanged). As a special case in command
substitutions, a command of the form < file is interpreted to mean substitute the contents
of file ($(< foo) has the same effect as $(cat foo), but it is carried out more effi-
ciently because no process is started).
NOTE: $(command) expressions are currently parsed by finding the matching parenthesis,
regardless of quoting. This will hopefully be fixed soon.
Arithmetic substitutions are replaced by the value of the specified expression. For exam-
ple, the command echo $((2+3*4)) prints 14. See Arithmetic Expressions for a description
of an expression.
Parameters
Parameters are shell variables; they can be assigned values and their values can be
accessed using a parameter substitution. A parameter name is either one of the special
single punctuation or digit character parameters described below, or a letter followed by
zero or more letters or digits ('_' counts as a letter). The later form can be treated as
arrays by appending an array index of the form: [expr] where expr is an arithmetic expres-
sion. Array indicies are currently limited to the range 0 through 1023, inclusive.
Parameter substitutions take the form $name, ${name} or ${name[expr]}, where name is a
parameter name. If substitution is performed on a parameter (or an array parameter ele-
ment) 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, etc.; this is the only way the special single character
parameters are set. Second, parameters are imported from the shell's environment at
startup. Third, parameters can be assigned values on the command line, for example,
'FOO=bar' sets the parameter FOO to bar; multiple parameter assignments can be given on a
single command line and they can be followed by a simple-command, in which case the
assignments are in effect only for the duration of the command (such assignments are also
exported, see below for implications of this). Note that both the parameter name and the
= must be unquoted for the shell to recognize a parameter assignment. The fourth way of
setting a parameter is with the export, readonly and typeset commands; see their descrip-
tions in the Command Execution section. Fifth, for and select loops set parameters as
well as the getopts, read and set -A commands. Lastly, parameters can be assigned values
using assignment operators inside arithmetic expressions (see Arithmetic Expressions
below) or using the ${name=value} form of parameter substitution (see below).
Parameters with the export attribute (set using the export or typeset -x commands, or by
parameter assignments followed by simple commands) are put in the environment (see envi-
ron(5)) of commands run by the shell as name=value pairs. The order in which parameters
appear in the environment of a command is unspecified. When the shell starts up, it
extracts parameters and their values from its environment and automatically sets the
export attribute for those parameters.
Modifiers can be applied to the ${name} form of parameter substitution:
${name:-word}
if name is set and not null, it is substituted, otherwise word is substituted.
${name:+word}
if name is set and not null, word is substituted, otherwise nothing is substituted.
${name:=word}
if name is set and not null, it is substituted, otherwise it is assigned word and
the resulting value of name is substituted.
${name:?word}
if name is set and not null, it is substituted, otherwise word is printed on stan-
dard error (preceded by name:) and an error occurs (normally causing termination of
a shell script, function or .-script). If word is omitted the string 'parameter
null or not set' is used instead.
In the above modifiers, the : can be omitted, in which case the conditions only depend on
name being set (as opposed to set and not null). If word is needed, parameter, command,
arithmetic and tilde substitution are performed on it; if word is not needed, it is not
evaluated.
The following forms of parameter substitution can also be used:
${#name}
The number of positional parameters if name is *, @ or is not specified, or the
length of the string value of parameter name.
${#name[*]}, ${#name[@]}
The number of elements in the array name.
${name#pattern}, ${name##pattern}
If pattern matches the beginning of the value of parameter name, the matched text
is deleted from the result of substitution. A single # results in the shortest
match, two #'s results in the longest match.
${name%pattern}, ${name%%pattern}
Like ${..#..} substitution, but it deletes from the end of the value.
The following special parameters are implicitly set by the shell and cannot be set
directly using assignments:
! Process id of the last background process started. If no background processes have
been started, the parameter is not set.
# The number of positional parameters (i.e., $1, $2, etc.).
$ The process ID of the shell, or the PID of the original shell if it is a subshell.
- The concatenation of the current single letter options (see set command below for
list of options).
? The exit status of the last non-asynchronous command executed. If the last command
was killed by a signal, $? is set to 128 plus the signal number.
0 The name the shell was invoked with (i.e., argv[0]), or the command-name if it was
invoked with the -c option and the command-name was supplied, or the file argument,
if it was supplied. If the posix option is not set, $0 is the name of the current
function or script.
1 ... 9
The first nine positional parameters that were supplied to the shell, function or
.-script. Further positional parameters may be accessed using ${number}.
* All positional parameters (except parameter 0), i.e., $1 $2 $3.... If used outside
of double quotes, parameters are separate words (which are subjected to word split-
ting); if used within double quotes, parameters are separated by the first charac-
ter 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 loos-
ing null arguments or splitting arguments with spaces).
The following parameters are set and/or used by the shell:
_ (underscore)
When an external command is executed by the shell, this parameter is set in the
environment of the new process to the path of the executed command. In interactive
use, this parameter is also set in the parent shell to the last word of the
previous command. When MAILPATH messages are evaluated, this parameter contains
the name of the file that changed (see MAILPATH parameter below).
CDPATH Search path for the cd built-in command. Works the same way as PATH for those
directories not beginning with / in cd commands. Note that if CDPATH is set and
does not contain . nor an empty path, the current directory is not searched.
COLUMNS
Set to the number of columns on the terminal or window. Currently set to the cols
value as reported by stty(1) if that value is non-zero. This parameter is used by
the interactive line editing modes, and by select, set -o and kill -l commands to
format information in columns.
EDITOR If the VISUAL parameter is not set, this parameter controls the command line edit-
ing mode for interactive shells. See VISUAL parameter below for how this works.
ENV If this parameter is found to be set after any profile files are executed, the
expanded value is used as a shell start-up file. It typically contains function
and alias definitions.
ERRNO Integer value of the shell's errno variable -- indicates the reason the last system
call failed.
Not implemented yet.
EXECSHELL
If set, this parameter is assumed to contain the shell that is to be used to exe-
cute commands that execve(2) fails to execute and which do not start with a '#!
shell' sequence.
FCEDIT The editor used by the fc command (see below).
FPATH Like PATH, but used when an undefined function is executed to locate the file
defining the function. It is also searched when a command can't be found using
PATH. See Functions below for more information.
HISTFILE
The name of the file used to store history. When assigned to, history is loaded
from the specified file. Also, several invocations of the shell running on the
same machine will share history if their HISTFILE parameters all point at the same
file.
NOTE: if HISTFILE isn't set, no history file is used. This is different from the
original Korn shell, which uses $HOME/.sh_history; in future, pdksh may also use a
default history file.
HISTSIZE
The number of commands normally stored for history, default 128.
HOME The default directory for the cd command and the value substituted for an unquali-
fied ~ (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.
KSH_VERSION
The version of shell and the date the version was created (readonly). See also the
version commands in Emacs Editing Mode and Vi Editing Mode sections, below.
LINENO The line number of the function or shell script that is currently being executed.
LINES Set to the number of lines on the terminal or window.
Not implemented yet.
MAIL If set, the user will be informed of the arrival of mail in the named file. This
parameter is ignored if the MAILPATH parameter is set.
MAILCHECK
How often, in seconds, the shell will check for mail in the file(s) specified by
MAIL or MAILPATH. If 0, the shell checks before each prompt. The default is 600
(10 minutes).
MAILPATH
A list of files to be checked for mail. The list is colon separated, and each file
may be followed by a ? and a message to be printed if new mail has arrived. Com-
mand, parameter and arithmetic substitution is performed on the message, and, dur-
ing substitution, the parameter $_ contains the name of the file. The default mes-
sage is you have mail in $_.
OLDPWD The previous working directory. Unset if cd has not successfully changed directo-
ries since the shell started, or if the shell doesn't know where it is.
OPTARG When using getopts, it contains the argument for a parsed option, if it requires
one.
OPTIND The index of the last argument processed when using getopts. Assigning 1 to this
parameter causes getopts to process arguments from the beginning the next time it
is invoked.
PATH A colon separated list of directories that are searched when looking for commands
and .'d files. An empty string resulting from a leading or trailing colon, or two
adjacent colons is treated as a '.', the current directory.
POSIXLY_CORRECT
If set, this parameter causes the posix option to be enabled. See POSIX Mode
below.
PPID The process ID of the shell's parent (readonly).
PS1 PS1 is the primary prompt for interactive shells. Parameter, command and arith-
metic substitutions are performed, and ! is replaced with the current command num-
ber (see fc command below). A literal ! can be put in the prompt by placing !! in
PS1. Note that since the command line editors try to figure out how long the
prompt is (so they know how far it is to edge of the screen), escape codes in the
prompt tend to mess things up. You can tell the shell not to count certain
sequences (such as escape codes) by prefixing your prompt with a non-printing char-
acter (such as control-A) followed by a carriage return and then delimiting the
escape codes with this non-printing character. If you don't have any non-printing
characters, you're out of luck... BTW, don't blame me for this hack; it's in the
original ksh. Default is '$ ' for non-root users, '# ' for root..
PS2 Secondary prompt string, by default '> ', used when more input is needed to com-
plete a command.
PS3 Prompt used by select statement when reading a menu selection. Default is '#? '.
PS4 Used to prefix commands that are printed during execution tracing (see set -x com-
mand below). Parameter, command and arithmetic substitutions are performed before
it is printed. Default is '+ '.
PWD The current working directory. Maybe unset or null if shell doesn't know where it
is.
RANDOM A simple random number generator. Every time RANDOM is referenced, it is assigned
the next number in a random number series. The point in the series can be set by
assigning a number to RANDOM (see rand(3)).
REPLY Default parameter for the read command if no names are given. Also used in select
loops to store the value that is read from standard input.
SECONDS
The number of seconds since the shell started or, if the parameter has been
assigned an integer value, the number of seconds since the assignment plus the
value that was assigned.
TMOUT If set to a positive integer in an interactive shell, it specifies the maximum num-
ber of seconds the shell will wait for input after printing the primary prompt
(PS1). If the time is exceeded, the shell exits.
TMPDIR The directory shell temporary files are created in. If this parameter is not set,
or does not contain the absolute path of a writable directory, temporary files are
created in /tmp.
VISUAL If set, this parameter controls the command line editing mode for interactive
shells. If the last component of the path specified in this parameter contains the
string vi, emacs or gmacs, the vi, emacs or gmacs (Gosling emacs) editing mode is
enabled, respectively.
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 (those preceding a simple-command or those occurring in the argu-
ments of alias, export, readonly, and typeset), tilde expansion is done after any unquoted
colon (:), and login names are also delimited by colons.
The home directory of previously expanded login names are cached and re-used. The alias
-d command may be used to list, change and add to this cache (e.g., 'alias -d
fac=/usr/local/facilities; cd ~fac/bin').
Brace Expansion (alternation)
Brace expressions, which take the form
prefix{str1,...,strN}suffix
are expanded to N words, each of which is the concatenation of prefix, stri and suffix
(e.g., 'a{c,b{X,Y},d}e' expands to four word: ace, abXe, abYe, and ade). As noted in the
example, brace expressions can be nested and the resulting words are not sorted. Brace
expressions must contain an unquoted comma (,) for expansion to occur (i.e., {} and {foo}
are not expanded). Brace expansion is carried out after parameter substitution and before
file name generation.
File Name Patterns
A file name pattern is a word containing one or more unquoted ? or * characters or [..]
sequences. Once brace expansion has been performed, the shell replaces file name patterns
with the sorted names of all the files that match the pattern (if no files match, the word
is left unchanged). The pattern elements have the following meaning:
? matches any single character.
* matches any sequence of characters.
[..] matches any of the characters inside the brackets. Ranges of characters can be
specified by separating two characters by a -, e.g., [a0-9] matches the letter a or
any digit. In order to represent itself, a - must either be quoted or the first or
last character in the character list. Similarly, a ] must be quoted or the first
character in the list if it is represent itself instead of the end of the list.
Also, a ! appearing at the start of the list has special meaning (see below), so
to represent itself it must be quoted or appear later in the list.
[!..] like [..], except it matches any character not inside the brackets.
*(pattern| ... |pattern)
matches any string of characters that matches zero or more occurances of the speci-
fied patterns. Example: the pattern *(foo|bar) matches the strings '', 'foo',
'bar', 'foobarfoo', etc..
+(pattern| ... |pattern)
matches any string of characters that matches one or more occurances of the speci-
fied patterns. Example: the pattern +(foo|bar) matches the strings 'foo', 'bar',
'foobarfoo', etc..
?(pattern| ... |pattern)
matches the empty string or a string that matches one of the specified patterns.
Example: the pattern ?(foo|bar) only matches the strings '', 'foo' and 'bar'.
@(pattern| ... |pattern)
matches a string that matches one of the specified patterns. Example: the pattern
@(foo|bar) only matches the strings 'foo' and 'bar'.
!(pattern| ... |pattern)
matches any string that does not match one of the specified patterns. Examples:
the pattern !(foo|bar) matches all strings except 'foo' and 'bar'; the pattern !(*)
matches no strings; the pattern !(?)* matches all strings (think about it).
Note that pdksh currently never matches . and .., but the original ksh, Bourne sh and bash
do, so this may have to change (too bad).
Note that none of the above pattern elements match either a period (.) at the start of a
file name or a slash (/), even if they are explicitly used in a [..] sequence; also, the
names . and .. are never matched, even by the pattern .*.
If the markdirs option is set, any directories that result from file name generation are
marked with a trailing /.
The POSIX character classes (i.e., [:class-name:] inside a [..] expression) are not yet
implemented.
Input/Output Redirection
When a command is executed, its standard input, standard output and standard error (file
descriptors 0, 1 and 2, respectively) are normally inherited from the shell. Three excep-
tions 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 dis-
abled, for which standard input is initially set to be from /dev/null, and commands for
which any of the following redirections have been specified:
> file standard output is redirected to file. If file does not exist, it is created; if
it does exist, is a regular file and the noclobber option is set, an error occurs,
otherwise the file is truncated. Note that this means the command cmd < foo > foo
will open foo for reading and then truncate it when it opens it for writing, before
cmd gets a chance to actually read foo.
>| file
same as >, except the file is truncated, even if the noclobber option is set.
>> file
same as >, except the file an existing file is appended to instead of being trun-
cated. 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 reading.
<> 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 substitu-
tions 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 char-
acter -, 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 sin-
gle digit. Parameter, command and arithmetic substitutions, tilde substitutions and (if
the shell is interactive) file name generation are all performed on the file, marker and
fd arguments of redirections. Note however, that the results of any file name generation
are only used if a single file is matched; if multiple files match, the word with the
unexpanded file name generation characters is used. Note that in restricted shells, redi-
rections which can create files cannot be used.
For simple-commands, redirections may appear anywhere in the command, for compound-com-
mands (if statements, etc.), any redirections must appear at the end. Redirections are
processed after pipelines are created and in the order they are given, so
cat /foo/bar 2>&1 > /dev/null | cat -n
will print an error with a line number prepended to it.
Arithmetic Expressions
Integer arithmetic expressions can be used with the let command, inside $((..)) expres-
sions, inside array references (e.g., name[expr]), as numeric arguments to the test com-
mand, and as the value of an assignment to an integer parameter.
Expression may contain alpha-numeric parameter identifiers, array references, and integer
constants and may be combined with the following C operators (listed and grouped in
increasing order of precedence).
Unary operators:
+ - ! ~ ++ --
Binary operators:
,
= *= /= %= += -= <<= >>= &= ^= |=
||
&&
|
^
&
== !=
< <= >= >
<< >>
+ -
* / %
Ternary operator:
?: (precedence is immediately higher than assignment)
Grouping operators:
( )
Integer constants may be specified with arbitrary bases using the notation base#number,
where base is a decimal integer specifying the base, and number is a number in the speci-
fied base.
The operators are evaluated as follows:
unary +
result is the argument (included for completeness).
unary -
negation.
! 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 expres-
sion) - the parameter is incremented by 1. When used as a prefix operator,
the result is the incremented value of the parameter, when used as a postfix
operator, the result is the original value of the parameter.
++ similar to ++, except the paramter is decremented by 1.
, separates two arithmetic expressions; the left hand side is evaluated first,
then the right. The result is value of the expression on the right hand
side.
= assignment; variable on the left is set to the value on the right.
*= /= %= += -= <<= >>= &= ^= |=
assignment operators; = is the same as = (
).
|| 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) exclusive-or.
& arithmetic (bit-wise) and.
== equal; the result is 1 if both arguments are equal, 0 if not.
!= 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 is non-zero, the result is , otherwise .
Co-Processes
A co-process, which is a pipeline created with the |& operator, is an asynchronous process
that the shell can both write to (using print -p) and read from (using read -p). The
input and output of the co-process can also be manipulated using >&p and <&p redirections,
respectively. Once a co-process has been started, another can't be started until the co-
process exits, or until the co-process input has been redirected using an exec n>&p redi-
rection. If a co-process's input is redirected in this way, the next co-process to be
started will share the output with the first co-process, unless the output of the initial
co-process has been redirected using an exec n<&p redirection.
Some notes concerning co-processes:
? the only way to close the co-process input (so the co-process reads an end-of-file)
is to redirect the input to a numbered file descriptor and then close that file
descriptor (e.g., exec 3>&p;exec 3>&-).
? in order for co-processes to share a common output, the shell must keep the write
portion of the output pipe open. This means that end of file will not be detected
until all co-processes sharing the co-process output have exited (when they all
exit, the shell closes its copy of the pipe). This can be avoided by redirecting
the output to a numbered file descriptor (as this also causes the shell to close
its copy). Note that this behaviour is slightly different from the original Korn
shell which closes its copy of the write portion of the co-processs output when the
most recently started co-process (instead of when all sharing co-processes) exits.
? print -p will ignore SIGPIPE signals during writes if the signal is not being
trapped or ignored; the same is not true if the co-process input has been dupli-
cated to another file descriptor and print -un is used.
Functions
Functions are defined using either Korn shell function name syntax or the Bourne/POSIX
shell name() syntax (see below for the difference between the two forms). Functions are
like .-scripts in that they are executed in the current environment, however, unlike
.-scripts, shell arguments (i.e., positional parameters, $1, etc.) are never visible
inside them. When the shell is determining the location of a command, functions are
searched after special built-in commands, and 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.
autoload (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 exe-
cuted. If after executing the file, the named function is found to be defined, the func-
tion 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 undoc-
umented 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 functions 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 executed.
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:
? the $0 parameter is set to the name of the function (Bourne-style functions leave
$0 untouched).
? parameter assignments preceeding function calls are not kept in the shell environ-
ment (executing Bourne-style functions will keep assignments).
? 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 function). In the future, the following differences will also
be added:
? 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 function.
? 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, how-
ever this is usually not desirable).
The following is a list of things that are affected by the state of the posix option:
? \" inside double quoted '..' command substitutions: in posix mode, the \" is inter-
preted 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.
? kill -l output: in posix mode, signal names are listed one a single line; in non-
posix mode, signal numbers, names and descriptions are printed in columns. In
future, a new option (-v perhaps) will be added to distinguish the two behaviours.
? 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.
? eval exit status: if eval gets to see an empty command (e.g., eval "'false'"), its
exit status in posix mode will be 0. In non-posix mode, it will be the exit status
of the last command substitution that was done in the processing of the arguments
to eval (or 0 if there were no command substitutions).
? getopts: in posix mode, options must start with a -; in non-posix mode, options can
start with either - or +.
? brace expansion (also known as alternation): in posix mode, brace expansion is dis-
abled; in non-posix mode, brace expansion enabled. Note that set -o posix (or set-
ting the POSIXLY_CORRECT parameter) automatically turns the braceexpand option off,
however it can be explicitly turned on later.
? set -: in posix mode, this does not clear the verbose or xtrace options; in non-
posix mode, it does.
? 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 $?' prints 0 in
posix mode, 1 in non-posix mode. This construct is used in most shell scripts that
use the old getopt(1) command.
? argument expansion of alias, export, readonly, and typeset commands: in posix mode,
normal argument expansion done; in non-posix mode, field splitting, file globing,
brace expansion and (normal) tilde expansion are turned off, and assignment tilde
expansion is turned on.
? signal specification: in posix mode, signals can be specified as digits only if
signal numbers match POSIX values (i.e., HUP=1, INT=2, QUIT=3, ABRT=6, KILL=9,
ALRM=14, and TERM=15); in non-posix mode, signals can be always digits.
? alias expansion: in posix mode, alias expansion is only carried out when reading
command words; in non-posix mode, alias expansion is carried out on any word fol-
lowing an alias that ended in a space. For example, the following for loop
alias a='for ' i='j'
a i in 1 2; do echo i=$i j=$j; done
uses parameter i in posix mode, j in non-posix mode.
? 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 (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 param-
eter 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 set command below) some special commands are very special in that no field splitting,
file globing, brace expansion nor tilde expansion is preformed 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
. continue exit return trap
: eval export set unset
break exec readonly shift
Additional ksh special commands
builtin times typeset
Very special commands (non-posix mode)
alias readonly set typeset
POSIX regular commands
alias command fg kill umask
bg false getopts read unalias
cd fc jobs true wait
Additional ksh regular commands
[ let pwd ulimit
echo print test whence
In the future, the additional ksh special and regular commands may be treated differently
from the POSIX special and regular commands.
Once the type of the 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 [arg1 ...]
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] ] [?px] [?] [name1[=value1] ...]
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. In addition, if the -p option is
used, each alias is prefixed with the string "alias ".
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
affect).
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 -d causes directory aliases, which are used in tilde expansion, to be listed or
set (see Tilde Expansion above).
bg [job ...]
Resume the specified stopped job(s) in the background. If no jobs are specified,
%+ is assumed. This command is only available on systems which support job con-
trol. See Job Control below for more information.
bind [-m] [key[=editing-command] ...]
Set or view the current emacs command editing key bindings/macros. See Emacs Edit-
ing Mode below for a complete description.
break [level]
break exits the levelth inner most for, select, until, or while loop. level
defaults to 1.
builtin command [arg1 ...]
Execute the built-in command command.
cd [-LP] [dir]
Set the working directory to dir. If the parameter CDPATH is set, it lists direc-
tories to search in for dir. dir. An empty entry in the CDPATH entry means the
current directory. If a non-empty directory from CDPATH is used, the resulting
full path is printed to standard output. If dir is missing, the home directory
$HOME is used. If dir is -, the previous working directory is used (see OLDPWD
parameter). If -L option (logical path) is used or if the physical option (see set
command below) isn't set, references to .. in dir are relative to the path used get
to the directory. If -P option (physical path) is used or if the physical option
is set, .. is relative to the filesystem directory tree. The PWD and OLDPWD param-
eters are updated to reflect the current and old wording 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 [-pvV] cmd [arg1 ...]
If neither the -v nor -V options are given, cmd is executed exactly as if the com-
mand had not been specified, with two exceptions: first, cmd cannot be a shell
function, and second, special built-in commands lose their specialness (i.e., redi-
rection 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 sys-
tem dependent: on POSIXish systems, it is the value returned by
getconf CS_PATH
).
If the -v option is given, instead of executing cmd, information about what would
be executed is given (and the same is done for arg1 ...): for special and regular
built-in commands and functions, their names are simply printed, for aliases, a
command that defines them is printed, and for commands found by searching the PATH
parameter, the full path of the command is printed. If no command is be found,
(i.e., the path search fails), nothing is printed and command exits with a non-zero
status. The -V option is like the -v option, except it is more verbose.
continue [levels]
continue jumps to the beginning of the levelth inner most for, select, until, or
while loop. level defaults to 1.
echo [-neE] [arg ...]
Prints its arguments (separated by spaces) followed by a newline, to standard out.
The newline is suppressed if any of the arguments contain the backslash sequence
\c. See print command below for a list of other backslash sequences that are rec-
ognized.
The options are provided for compatibility with BSD shell scripts: -n suppresses
the trailing newline, -e enables backslash interpretation (a no-op, since this is
normally done), and -E which suppresses backslash interpretation.
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 process.
If no arguments are given, any IO redirection is permanent and the shell is not
replaced. Any file descriptors greater than 2 which are opened or dup(2)-ed in
this way are not made available to other executed commands (i.e., commands that are
not built-in to the shell). Note that the Bourne shell differs here: it does pass
these file descriptors on.
exit [status]
The shell exits with the specified exit status. If status is not specified, the
exit status is the current value of the ? parameter.
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 param-
eters 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 editor | -l [-n]] [-r] [first [last]]
first and last select commands from the history. Commands can be selected by his-
tory number, or a string specifying the most recent command starting with that
string. The -l option lists the command on stdout, and -n inhibits the default
command numbers. The -r option reverses the order of the list. Without -l, the
selected commands are edited by the editor specified with the -e option, or if no
-e is specified, the editor specified by the FCEDIT parameter (if this parameter is
not set, /bin/ed is used), and then executed by the shell.
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. 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. This command is only available on systems which support job control. See
Job Control below for more information.
getopts optstring name [arg ...]
getopts is 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 next argument to be processed 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 ques-
tion 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. An error message is also printed to standard error if optstring does not
begin with a colon.
When the end of the options is encountered, getopts exits with a non-zero exit sta-
tus. 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 invoked).
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 unex-
pected 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 where a command name and added to the hash table if it is an exe-
cutable command.
jobs [-lpn] [job ...]
Display information about the specified jobs; 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 pro-
cess-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 job.
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 signal TERM 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 name of the signal that killed a process which exited with the specified
exit-statuses. If no arguments are specified, a list of all the signals, their
numbers and a short description of them are printed.
let [expression ...]
Each expression is evaluated, see Arithmetic Expressions above. If all expressions
are successfully evaluated, the exit status is 0 (1) if the last expression evalu-
ated to non-zero (zero). If an error occurs during the parsing or evaluation of an
expression, the exit status is greater than 1. Since expressions may need to be
quoted, (( expr )) is syntactic sugar for let "expr".
print [-nprsun | -R [-en]] [argument ...]
Print prints its arguments on the standard output, separated by spaces, and termi-
nated 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, the -u option prints to file descrip-
tor n (n defaults to 1 if omitted), and the -p option prints to the co-process (see
Co-Processes above).
The -R option is used to emulate, to some degree, the BSD echo command, which does
not process \ sequences unless the -e option is given. As above, the -n option
suppresses the trailing newline.
pwd [-LP]
Print the present working directory. If -L option is used or if the physical
option (see set command below) isn't set, the logical path is printed (i.e., the
path used to cd to the current directory). If -P option (physical path) is used or
if the physical option is set, the path determined from the filesystem (by follow-
ing .. directories to the root directory) is printed.
read [-prsun] [parameter ...]
Reads a line of input from standard input, separate the line into fields using the
IFS parameter (see Substitution above), and assign 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 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 (e.g., read nfoo?'number of foos: ').
The -un and -p options cause input to be read from file descriptor n or the current
co-process (see Co-Processes above for comments on this), respectively. If the -s
option is used, input is saved to the history file.
readonly [-p] [parameter[=value]] ...
Sets the readonly attribute of the named parameters. If values are given, parame-
ters 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 readonly
attribute are printed one per line, unless the -p option is used, in which case
readonly commands defining all readonly 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 pro-
files as . scripts.
set [?abCefhkmnpsuvxX] [?o [option]] [?A name] [--] [arg ...]
The set command can be used to set (-) or clear (+) shell options, set the posi-
tional 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 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 args), the rest are left
untouched.
-a allexport all new parameters are created
with the export attribute
-b notify Print job notification mes-
sages asynchronously, instead
of just before the prompt.
Only used if job control is
enabled (-m).
-C noclobber Prevent > redirection from
overwriting existing files (>|
must be used to force an over-
write).
-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 || state-
ments.
-f noglob Do not expand file name pat-
terns.
-h trackall Create tracked aliases for all
executed commands (see Aliases
above). On by default for
non-interactive shells.
-i interactive Enable interactive mode - this
can only be set/unset when the
shell is invoked.
-k keyword Parameter assignments are rec-
ognized anywhere in a command.
-l login The shell is a login shell -
this can only be set/unset
when the shell is invoked (see
Shell Startup above).
-m monitor Enable job control (default
for interactive shells).
-n noexec Do not execute any commands -
useful for checking the syntax
of scripts (ignored if inter-
active).
-p privileged Set automatically if, when the
shell starts, the read uid or
gid does not match the effec-
tive uid or gid, respectively.
See Shell Startup above for a
description of what this
means.
-r restricted Enable restricted mode -- this
option can only be used when
the shell is invoked. See
Shell Startup 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 in the set
command, it causes the speci-
fied 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 param-
eter is treated as an error,
unless one of the -, + or =
modifiers is used.
-v verbose Write shell input to standard
error as it is read.
-x xtrace Print commands and parameter
assignments when they are exe-
cuted, preceded by the value
of PS4.
-X markdirs Mark directories with a trail-
ing / during file name genera-
tion.
bgnice Background jobs are run with
lower priority.
braceexpand Enable brace expansion (aka,
alternation).
emacs Enable BRL emacs-like command
line editing (interactive
shells only); see Emacs Edit-
ing Mode.
gmacs Enable gmacs-like (Gosling
emacs) command line editing
(interactive shells only);
currently identical to emacs
editing except that transpose
(^T) acts slightly differ-
ently.
ignoreeof The shell will not (easily)
exit on when end-of-file is
read, exit must be used. To
avoid infinite loops, the
shell will exit if eof is read
13 times in a row.
nohup Do not kill running jobs with
a HUP signal when a login
shell exists. 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
HUP 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' directo-
ries (i.e., the shell handles
.., which allows the user to
be obliveous of symlink links
to directories). Clear by
default. Note that setting
this option does not effect
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.
vi Enable vi-like command line
editing (interactive shells
only).
viraw No effect - in the original
Korn shell, unless viraw was
set, the vi command line mode
would let the tty driver do
the work until ESC (^[) was
entered. pdksh is always in
viraw mode.
vi-esccomplete In vi command line editing, do
command / 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, char-
acters in the range 128-160
are printed as is, which may
cause problems.
vi-tabcomplete In vi command line editing, do
command / file name completion
when tab (^I) is entered in
insert 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 are ended with -- and
there are no remaining arguments, all positional parameters are cleared. If no
options or arguments are given, then 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, and 1 status if
false and greater than 1 if there was an error. It is normally used as the condi-
tion command of if and while statements. The following basic expressions are
available:
str str has non-zero length.
Note that there is the
potential for problems if
str turns out to be an oper-
ator (e.g., -r) - it is gen-
erally better to use a test
like
[ X"str" != X
]
instead (double
quotes are used in
case str contains
spaces or file glob-
ing characters).
-r file file exists and is readable.
-w file file exists and is writable.
-x file file exists and is exe-
cutable.
-a file file exists.
-e file file exists.
-f file file is a regular file.
-d file file is a directory.
-c file file is a character special
device.
-b file file is a block special
device.
-p file file is a named pipe.
-u file file's mode has setuid bit
set.
-g file file's mode has setgid bit
set.
-k file file's mode has sticky bit
set.
-s file file is not empty.
-O file file's owner is the shell's
effective user-ID.
-G file file's group is the shell's
effective group-ID.
-h file file is a symbolic link.
-H file file is a context dependent
directory (only useful on
HP-UX).
-L file file is a symbolic link.
-S file file is a socket.
-o option shell option is set (see set
command above for 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 (thus
[ -o foo -o -o
!foo ]
returns true if and
only if option foo
exists).
file -nt file first file is newer than
second file or first file
exists and the second file
does not.
file -ot file first file is older than
second file or second file
exists and the first file
does not.
file -ef file first file is the same file
as second file.
-t [fd] file descriptor is a tty
device. If the posix option
(set -o posix, see POSIX
Mode above) 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 below).
string string is not empty.
-z string string is empty.
-n string string is not empty.
string = string strings are equal.
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). I.e., [ -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 argu-
ments 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 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.
time [-p] [ pipeline ]
If a pipeline is given, the times used to execute the pipeline are reported. If no
pipeline is given, then the user and system time used by the shell itself, and all
the commands it has run since it was started, are reported. The times reported are
the real time (elapsed time from start to finish), the user cpu time (time spent
running in user mode) and the system cpu time (time spent running in kernel mode).
Times are reported to standard error; the format of the output is:
0.00s real 0.00s user 0.00s system
unless the -p option is given (only possible if pipeline is a simple command), in
which case the output is slightly longer:
real 0.00
user 0.00
sys 0.00
(the number of digits after the decimal may vary from system to system). Note that
simple redirections of standard error do not effect the output of the time command:
time sleep 1 2> afile
{ time sleep 1; } 2> afile
times for the first command do not go to afile, but those of the second command do.
times Print the accumulated user and system times used by the shell and by processes
which have exited that the shell started.
trap [handler signal ...]
Sets 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 (-), indicating that the default action is to be taken for the
signals (see signal(2 or 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 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 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
can not 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 [[?Ulprtux] [-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 arg used, the current attributes of all parameters are
printed as typeset commands; if an option is given (or - wi
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