= Set built-in
:encoding: UTF-8
:lang: en
//:title: Yash manual - Set built-in

The dfn:[set built-in] sets shell options and positional parameters.

[[syntax]]
== Syntax

- +set [{{option}}s] [{{operand}}s]+
- +set -o+
- +set +o+

The set built-in requires that all options precede operands.
Any command line arguments after the first operand are all treated as
operands.

[[description]]
== Description

When executed without any command arguments, the built-in prints a list of all
existing link:params.html#variables[variables] to the standard input in a form
that can be reused as commands that will restore the variable definitions.

When +-o+ is the only command argument, the built-in prints a list of shell
options with their current settings.
When `+o` is the only command argument, the built-in prints commands that can
be reused to restore the current shell option settings.

In other cases, the built-in changes shell option settings and/or
link:params.html#positional[positional parameters].

[[options]]
== Options

When one or more options are specified, the built-in enables or disables the
shell options.
A normal hyphen-prefixed option enables a shell option.
An option that is prefixed with a plus (`+`) instead of a hyphen disables a
shell option.
For example, options +-m+, +-o monitor+, and +--monitor+ enable the monitor
option and options `+m`, `+o monitor`, `++monitor` disable it.

The name of a long option is case-insensitive and may include irrelevant
non-alphanumeric characters, which are ignored.
For example, options +--le-comp-debug+ and +--LeCompDebug+ are equivalent.
If +no+ is prepended to the name of a long option, the meaning is reversed.
For example, +--noallexport+ is equivalent to `++allexport` and `++nonotify`
to +--notify+.

An option can be specified in one of the following forms:

- a long option e.g. +--allexport+
- an +-o+ option with a option name specified as the argument
  e.g. +-o allexport+
- a single-character option e.g. +-a+

Not all options can be specified as single-character options.

The available options are:

[[so-allexport]]all-export (+-a+)::
When enabled, all link:params.html#variables[variables] are automatically
link:_export.html[exported] when assigned.

[[so-braceexpand]]brace-expand::
This option enables link:expand.html#brace[brace expansion].

[[so-caseglob]]case-glob::
(Enabled by default)
When enabled, pattern matching is case-insensitive in
link:expand.html#glob[pathname expansion].

[[so-clobber]]clobber (`+C`)::
(Enabled by default)
When enabled, the +>+ link:redir.html#file[redirection] behaves the same as
the +>|+ redirection.

[[so-curasync]]cur-async::
[[so-curbg]]cur-bg::
[[so-curstop]]cur-stop::
(Enabled by default)
These options affect choice of the current job
(cf. link:job.html#jobid[job ID]).

[[so-dotglob]]dot-glob::
When enabled, periods at the beginning of filenames are not treated specially
in link:expand.html#glob[pathname expansion].

[[so-emacs]]emacs::
This option enables link:lineedit.html[line-editing] in the
link:lineedit.html#modes[emacs mode].

[[so-errexit]]err-exit (+-e+)::
When enabled, if a link:syntax.html#pipelines[pipeline] ends with a non-zero
exit status, the shell immediately exits unless the pipeline is a condition of
an link:syntax.html#if[if command] or link:syntax.html#while-until[while or
until loop] or is prefixed by +!+.

[[so-exec]]exec (`+n`)::
(Enabled by default)
Commands are actually executed only when this option is enabled.
Otherwise, commands are just parsed and not executed.
Disabling this option may be useful for syntax checking.
In an link:interact.html[interactive shell], this option is always assumed
enabled.

[[so-extendedglob]]extended-glob::
This option enables link:expand.html#extendedglob[extension in pathname
expansion].

[[so-glob]]glob (`+f`)::
(Enabled by default)
This option enables link:expand.html#glob[pathname expansion].

[[so-hashondef]]hash-on-def (+-h+)::
When a link:exec.html#function[function] is defined when this option is
enabled, the shell immediately performs link:exec.html#search[command path
search] for each command that appears in the function and caches the command's
full path.

[[so-histspace]]hist-space::
When enabled, command lines that start with a whitespace are not saved in
link:interact.html#history[command history].

[[so-ignoreeof]]ignore-eof::
When enabled, an link:interact.html[interactive shell] does not exit when EOF
(end of file) is input.
This prevents the shell from exiting when you accidentally hit Ctrl-D.

[[so-lealwaysrp]]le-always-rp::
[[so-lecompdebug]]le-comp-debug::
[[so-leconvmeta]]le-conv-meta::
[[so-lenoconvmeta]]le-no-conv-meta::
[[so-lepromptsp]]le-prompt-sp::
[[so-levisiblebell]]le-visible-bell::
See link:lineedit.html#options[shell options on line-editing].

[[so-markdirs]]mark-dirs::
When enabled, resulting directory names are suffixed by a slash in
link:expand.html#glob[pathname expansion].

[[so-monitor]]monitor (+-m+)::
This option enables link:job.html[job control].
This option is enabled by default for an link:interact.html[interactive
shell].

[[so-notify]]notify (+-b+)::
When the status of a link:job.html[job] changes when this option is enabled,
the shell immediately notifies at any time.
This option overrides the notify-le option.

[[so-notifyle]]notify-le::
This option is similar to the notify option, but the status change is notified
only while the shell is waiting for input with
link:lineedit.html[line-editing].

[[so-nullglob]]null-glob::
When enabled, in link:expand.html#glob[pathname expansion], patterns that do
not match any pathname are removed from the command line rather than left as
is.

[[so-posixlycorrect]]posixly-correct::
This option enables the link:posix.html[POSIXly-correct mode].

[[so-unset]]unset (`+u`)::
(Enabled by default)
When enabled, undefined parameters are expanded to empty strings in
link:expand.html#params[parameter expansion].
When disabled, expansion of undefined parameter results in an error.

[[so-verbose]]verbose (+-v+)::
When enabled, the shell prints each command line to the standard error before
parsing and executing it.

[[so-vi]]vi::
This option enables link:lineedit.html[line-editing] in the
link:lineedit.html#modes[vi mode].
This option is enabled by default in an link:interact.html[interactive shell]
if the standard input and error are both terminals.

[[so-xtrace]]x-trace (+-x+)::
When enabled, the results of link:expand.html[expansion] are printed to the
standard error for each link:syntax.html#simple[simple command] being
executed.
When printed, each line is prepended with an expansion result of the
link:params.html#sv-ps4[+PS4+ variable].

[[operands]]
== Operands

If one or more operands are passed to the set built-in, current
link:params.html#positional[positional parameters] are all removed and the
operands are set as new positional parameters.
If the +--+ separator (cf. link:builtin.html#argsyntax[syntax of command
arguments]) is passed, the positional parameters are set even when there are
no operands, in which case new positional parameters will be nothing.

[[exitstatus]]
== Exit status

The exit status of the set built-in is zero unless there is any error.

[[notes]]
== Notes

The set built-in is a link:builtin.html#types[special built-in].

In the POSIX standard, available shell options are much limited.
The standard does not define:

- long options such as +--allexport+,
- prepending +no+ to negate an option,
- using uppercase alphabets and/or non-alphanumeric characters in option names

The options defined in the standard are:

- +-a+, +-o allexport+
- +-e+, +-o errexit+
- +-m+, +-o monitor+
- +-C+, +-o noclobber+
- +-n+, +-o noexec+
- +-f+, +-o noglob+
- +-b+, +-o notify+
- +-u+, +-o nounset+
- +-v+, +-o verbose+
- +-x+, +-o xtrace+
- +-h+
- +-o ignoreeof+
- +-o nolog+
- +-o vi+

Yash does not support the nolog option, which prevents
link:syntax.html#funcdef[function definitions] from being added to
link:interact.html#history[command history].

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