set, unset, setenv, unsetenv, export - shell built-in functions to determine the characteristics for environmental variables of the current shell and its descendents
SYNOPSIS
sh
set [--aefhkntuvx [argument]]...
unset [name]...
export [name]...
csh
set [var [= value]]
setvar [n] = word
unsetpattern
setenv [VAR [word]]
unsetenvvariable
ksh
set [±abCefhkmnopstuvx] [±o option]... [±A name]
[arg]...
The set built-in command has the following options:
--
Does not change any of the flags. This option is useful in setting $1 to -.
-a
Marks variables which are modified or created for export.
-e
Exits immediately if a command exits with a non-zero exit status.
-f
Disables file name generation.
-h
Locates and remembers function commands as functions are defined. Function commands are normally located when the function is executed.
-k
All keyword arguments are placed in the environment for a command, not just those that precede the command name.
-n
Reads commands but does not execute them.
-t
Exits after reading and executing one command.
-u
Treats unset variables as an error when substituting.
-v
Prints shell input lines as they are read.
-x
Prints commands and their arguments as they are executed.
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 can be found in $-. The remaining arguments are positional
parameters and are assigned, in order, to $1, $2, .... If no arguments are specified the values of all names are printed.
For each name, unset removes the corresponding variable or function value. The variables PATH, PS1, PS2, MAILCHECK, and IF cannot be unset.
With the export built-in, the specified names are marked for automatic export to the environment of subsequently executed commands. If no arguments are specified, variable names that have been marked for export during
the current shell's execution are listed. Function names are not exported.
csh
With no arguments, set displays the values of all shell variables. Multiword values are displayed as a parenthesized list. With the var argument alone, set assigns an empty (null) value to the variable var.
With arguments of the form var=valueset assigns value to var, where value is one of:
word
A single word (or quoted string).
(wordlist)
A space-separated list of words enclosed in parentheses.
Values are command and filename expanded before being assigned. The form setvar[n]=word replaces the n'th word in a multiword
value with word.
unset removes variables whose names match (filename substitution) pattern. All variables are removed by `unset *'.
With no arguments, setenv displays all environment variables. With the VAR argument, setenv sets the environment variable VAR to an empty (null) value. (By convention,
environment variables are normally specified upper-case names.) With both VAR and word arguments specified, setenv sets VAR to word, which must be either a single word
or a quoted string. The PATH variable can take multiple word arguments, separated by colons (see EXAMPLES). The most commonly used environment variables, USER, TERM, and PATH, are automatically imported to and
exported from the csh variables user, term, and path. Use setenv if you need to change these variables. In addition, the shell sets the PWD environment variable from the csh variable cwd whenever the latter changes.
The environment variables LC_CTYPE, LC_MESSAGES, LC_TIME, LC_COLLATE, LC_NUMERIC, and LC_MONETARY take immediate effect when changed within the C shell. See environ(5) for descriptions of these environment variables.
unsetenv removes variable from the environment. As with unset, pattern matching is not performed.
ksh
The flags for the set built-in have meaning as follows:
-A
Array assignment. Unsets the variable name and assigns values sequentially from the list arg. If +A is used, the variable name is not unset first.
-a
All subsequent variables that are defined are automatically exported.
-b
Causes the shell to notify the user asynchronously of background job completions.
-C
Prevents existing files from being overwritten by the shell's > redirection operator. The >| redirection operator overrides this noclobber option for an individual file.
-e
If a command has a non-zero exit status, executes the ERR trap, if set, and exits. This mode is disabled while reading profiles.
-f
Disables file name generation.
-h
Each command becomes a tracked alias when first encountered.
-k
All variable assignment arguments are placed in the environment for a command, not just those that precede the command name.
-m
Background jobs run in a separate process group and a line prints upon completion. The exit status of background jobs is reported in a completion message. On systems with job control, this flag is turned on automatically for interactive shells.
-n
Reads commands and checks them for syntax errors, but does not execute them. Ignored for interactive shells.
+o
Writes the current option stettings to standard output in a format that is suitable for reinput to the shell as commands that achieve the same option settings.
-ooption
The option argument can be one of the following option names:
allexport
Same as -a.
errexit
Same as -e.
bgnice
All background jobs are run at a lower priority. This is the default mode. emacs Puts you in an emacs style in-line editor for command entry.
gmacs
Puts you in a gmacs style in-line editor for command entry.
ignoreeof
The shell does not exit on end-of-file. The command exit must be used.
keyword
Same as -k.
markdirs
All directory names resulting from file name generation have a trailing / appended.
monitor
Same as -m.
noclobber
Prevents redirection operator > from truncating existing files. Requires the >| operator to truncate a file when turned on. Same as -C.
noexec
Same as -n.
noglob
Same as -f.
nolog
Does not save function definitions in history file.
notify
Same as -b.
nounset
Same as -u.
privileged
Same as -p.
verbose
Same as -v.
trackall
Same as -h.
vi
Puts you in insert mode of a vi style in-line editor until you hit escape character 033. This puts you in control mode. A return sends the line.
viraw
Each character is processed as it is typed in vi mode.
xtrace
Same as -x.
If no option name is supplied then the current option settings are printed.
-p
Disables processing of the $HOME/.profile file and uses the file /etc/suid_profile instead of the ENV file. This mode is on whenever the effective uid is not equal to the real uid, or when the effective gid is not equal to
the real gid. Turning this off causes the effective uid and gid to be set to the real uid and gid.
-s
Sorts the positional parameters lexicographically.
-t
Exits after reading and executing one command.
-u
Treats unset parameters as an error when substituting.
-v
Prints shell input lines as they are read.
-x
Prints commands and their arguments as they are executed.
-
Turns off -x and -v flags and stops examining arguments for flags.
-
Does not change any of the flags. This option 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 can 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 specified then the names and values of all variables are printed on the standard output.
The variables specified by the list of names are unassigned, that is, their values and attributes are erased. readonly variables cannot be unset. If the -f flag 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.
When using unset, the variables specified by the list of names are unassigned, i.e., their values and attributes are erased. readonly variables cannot be unset. If the -f, flag 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.
With the export built-in, the specified names are marked for automatic export to the environment of subsequently-executed commands.
When -p is specified, export writes to the standard output the names and values of all exported variables in the following format:
"export %s=%s\n", name, value
if name is set, and:
"export %s\n", name
if name is unset.
The shell formats the output, including the proper use of quoting, so that it is suitable for reinput to the shell as commands that achieve the same exporting results, except for the following:
1.
Read-only variables with values cannot be reset.
2.
Variables that were unset at the time they were output are not reset to the unset state if a value is assigned to the variable between the time the state was saved and the time at which the saved output is reinput to the shell.
On this manual page, ksh(1) commands that are preceded by one or two * (asterisks) are treated specially in the following ways:
1.
Variable assignment lists preceding the command remain in effect when the command completes.
2.
I/O redirections are processed after variable assignments.
3.
Errors cause a script that contains them to abort.
4.
Words, following a command preceded by ** that are in the format of a variable assignment, are expanded with the same rules as a variable assignment. This means that tilde substitution is performed after the = sign and word splitting and file
name generation are not performed.
ksh93
set sets or unsets options and positional parameters. Options that are specified with a - cause the options to be set. Options that are specified with a + cause the option to be unset.
set without any options or arguments displays the names and values of all shell variables in the order of the collation sequence in the current locale. The values are quoted so that they are suitable for input again to the shell.
If no arguments are specified, not even the end of options argument --, the positional parameters are unchanged. Otherwise, unless the -A option has been specified, the positional parameters are replaced by the list of arguments. A first argument of -- is ignored when setting positional parameters.
For backwards compatibility, a set command without any options specified, whose first argument is - turns off the -v and -x options. If any additional arguments are specified, they replace the positional parameters.
The options for set in ksh93 are:
-a
Set the export attribute for each variable whose name does not contain a . that you assign a value in the current shell environment.
-Aname
Assign the arguments sequentially to the array named by name starting at subscript 0 rather than to the positional parameters.
-b
The shell writes a message to standard error as soon it detects that a background job completes rather than waiting until the next prompt.
-B
Enable {...} group expansion. On by default.
-C
Prevents existing regular files from being overwritten using the > redirection operator. The >| redirection overrides this noclobber option.
-e
A simple command that has a non-zero exit status causes the shell to exit unless the simple command is:
o
contained in an && or || list
o
the command immediately following if, while, or until
o
contained in the pipeline following !
-f
Pathname expansion is disabled.
-G
Causes ** by itself to also match all sub-directories during pathname expansion.
-h
Obsolete. Causes each command whose name has the syntax of an alias to become a tracked alias when it is first encountered.
-H
Enable !-style history expansion similar to csh.
-k
This is obsolete. All arguments of the form name=value are removed and placed in the variable assignment list for the command. Ordinarily, variable assignments must precede command arguments.
-m
When enabled, the shell runs background jobs in a separate process group and displays a line upon completion. This mode is enabled by default for interactive shells on systems that support job control.
-n
The shell reads commands and checks for syntax errors, but does not execute the command. Usually specified on command invocation.
-o [option]
If option is not specified, the list of options and their current settings is written to standard output. When invoked with a + the options are written in a format that can be input again to the shell to restore the settings. This option can be repeated to enable
or disable multiple options.
The value of option must be one of the following:
allexport
Same as -a.
bgnice
All background jobs are run at lower priorities.
braceexpand
Same as -B.
emacs
Enables or disables emacs editing mode.
errexit
Same as -e.
globstar
Equivalent to -G.
gmacs
Enables or disables gmacs. gmacs editing mode is the same as emacs editing mode, except for the handling of CTRL-T.
histexpand
Same as -H.
ignoreeof
The interactive shell does not exit on end-of-file.
keyword
Same as -k.
markdirs
All directory names resulting from file name generation have a trailing / appended.
monitor
Same as -m.
multiline
Use multiple lines when editing lines that are longer than the window width.
noclobber
Same as -C.
noexec
Same as -n.
noglob
Same as -f.
nolog
This has no effect. It is provided for backward compatibility.
notify
Same as -b.
nounset
Same as -u.
pipefail
A pipeline does not complete until all components of the pipeline have completed, and the exit status of the pipeline is the value of the last command to exit with non-zero exit status, or is zero if all commands return zero exit status.
privileged
Same as -p.
showme
Simple commands preceded by a ; are traced as if -x were enabled but not executed.
trackall
Same as -h.
verbose
Same as -v.
vi
Enables or disables vi editing mode.
viraw
Does not use canonical input mode when using vi edit mode
xtrace
Same as -x.
-p
Privileged mode. Disabling -p sets the effective user id to the real user id, and the effective group id to the real group id. Enabling -p restores the effective user and group ids to their values when the shell was invoked. The -p option
is on whenever the real and effective user id is not equal or the real and effective group id is not equal. User profiles are not processed when -p is enabled.
-r
Restricted. Enables restricted shell. This option cannot be unset once enabled.
-s
Sort the positional parameters
-t
Obsolete. The shell reads one command and then exits.
-u
If enabled, the shell displays an error message when it tries to expand a variable that is unset.
-v
Verbose. The shell displays its input onto standard error as it reads it.
-x
Execution trace. The shell displays each command after all expansion and before execution preceded by the expanded value of the PS4 parameter.
The following exit values are returned by set in ksh93:
0
Successful completion.
>0
An error occurred.
For each name specified, unset unsets the variable, or function if -f is specified, from the current shell execution environment. Read-only variables cannot be unset.
The options for unset in ksh93 are:
-f
Where name refers to a function name, the shell unsets the function definition.
-n
If name refers to variable that is a reference, the variable name is unset rather than the variable it references. Otherwise, this option is equivalent to the -v option.
-v
Where name refers to a variable name, the shell unsets it and removes it from the environment. This is the default behavior.
The following exit values are returned by unset in ksh93:
0
Successful completion. All names were successfully unset.
>0
An error occurred, or one or more name operands could not be unset
export sets the export attribute on each of the variables specified by name which causes them to be in the environment of subsequently executed commands. If =value is specified, the variable name is
set to value.
If no name is specified, the names and values of all exported variables are written to standard output.
export is built-in to the shell as a declaration command so that field splitting and pathname expansion are not performed on the arguments. Tilde expansion occurs on value.
The options for export in ksh93 are:
-p
Causes the output to be in the form of export commands that can be used as input to the shell to recreate the current exports.
The following exit values are returned by export in ksh93:
0
Successful completion.
>0
An error occurred.
On this manual page, ksh93(1) commands that are preceded by one or two + are treated specially in the following ways:
1.
Variable assignment lists preceding the command remain in effect when the command completes.
2.
I/O redirections are processed after variable assignments.
3.
Errors cause a script that contains them to abort.
4.
They are not valid function names.
5.
Words, following a command preceded by ++ that are in the format of a variable assignment, are expanded with the same rules as a variable assignment. This means that tilde substitution is performed after the = sign and field splitting and file
name generation are not performed.
EXAMPLES
csh
The following example sets the PATH variable to search for files in the /bin, /usr/bin, /usr/sbin, and /usr/ucb/bin directories, in that order:
setenv PATH "/bin:/usr/bin:/usr/sbin:usr/ucb/bin"
ATTRIBUTES
See attributes(5) for descriptions of the following attributes:
