If no options or arguments are specified, set shall write the
names and values of all shell variables in the collation sequence
of the current locale. Each name shall start on a separate line,
using the format:
"%s=%s\n", <name>, <value>
The value string shall be written with appropriate quoting; see
the description of shell quoting in Section 2.2, Quoting. The
output shall be suitable for reinput to the shell, setting or
resetting, as far as possible, the variables that are currently
set; read-only variables cannot be reset.
When options are specified, they shall set or unset attributes of
the shell, as described below. When arguments are specified, they
cause positional parameters to be set or unset, as described
below. Setting or unsetting attributes and positional parameters
are not necessarily related actions, but they can be combined in
a single invocation of set.
The set special built-in shall support the Base Definitions
volume of POSIX.1‐2017, Section 12.2, Utility Syntax Guidelines
except that options can be specified with either a leading
<hyphen-minus> (meaning enable the option) or <plus-sign>
(meaning disable it) unless otherwise specified.
Implementations shall support the options in the following list
in both their <hyphen-minus> and <plus-sign> forms. These options
can also be specified as options to sh.
-a When this option is on, the export attribute shall be set
for each variable to which an assignment is performed; see
the Base Definitions volume of POSIX.1‐2017, Section 4.23,
Variable Assignment. If the assignment precedes a utility
name in a command, the export attribute shall not persist
in the current execution environment after the utility
completes, with the exception that preceding one of the
special built-in utilities causes the export attribute to
persist after the built-in has completed. If the assignment
does not precede a utility name in the command, or if the
assignment is a result of the operation of the getopts or
read utilities, the export attribute shall persist until
the variable is unset.
-b This option shall be supported if the implementation
supports the User Portability Utilities option. It shall
cause the shell to notify the user asynchronously of
background job completions. The following message is
written to standard error:
"[%d]%c %s%s\n", <job-number>, <current>, <status>, <job-name>
where the fields shall be as follows:
<current> The character '+' identifies the job that would
be used as a default for the fg or bg
utilities; this job can also be specified using
the job_id "%+" or "%%". The character '-'
identifies the job that would become the
default if the current default job were to
exit; this job can also be specified using the
job_id "%-". For other jobs, this field is a
<space>. At most one job can be identified
with '+' and at most one job can be identified
with '-'. If there is any suspended job, then
the current job shall be a suspended job. If
there are at least two suspended jobs, then the
previous job also shall be a suspended job.
<job-number>
A number that can be used to identify the
process group to the wait, fg, bg, and kill
utilities. Using these utilities, the job can
be identified by prefixing the job number with
'%'.
<status> Unspecified.
<job-name> Unspecified.
When the shell notifies the user a job has been completed,
it may remove the job's process ID from the list of those
known in the current shell execution environment; see
Section 2.9.3.1, Examples. Asynchronous notification shall
not be enabled by default.
-C (Uppercase C.) Prevent existing files from being
overwritten by the shell's '>' redirection operator (see
Section 2.7.2, Redirecting Output); the ">|" redirection
operator shall override this noclobber option for an
individual file.
-e When this option is on, when any command fails (for any of
the reasons listed in Section 2.8.1, Consequences of Shell
Errors or by returning an exit status greater than zero),
the shell immediately shall exit, as if by executing the
exit special built-in utility with no arguments, with the
following exceptions:
1. The failure of any individual command in a multi-
command pipeline shall not cause the shell to exit.
Only the failure of the pipeline itself shall be
considered.
2. The -e setting shall be ignored when executing the
compound list following the while, until, if, or elif
reserved word, a pipeline beginning with the !
reserved word, or any command of an AND-OR list other
than the last.
3. If the exit status of a compound command other than a
subshell command was the result of a failure while -e
was being ignored, then -e shall not apply to this
command.
This requirement applies to the shell environment and each
subshell environment separately. For example, in:
set -e; (false; echo one) | cat; echo two
the false command causes the subshell to exit without
executing echo one; however, echo two is executed because
the exit status of the pipeline (false; echo one) | cat is
zero.
-f The shell shall disable pathname expansion.
-h Locate and remember utilities invoked by functions as those
functions are defined (the utilities are normally located
when the function is executed).
-m This option shall be supported if the implementation
supports the User Portability Utilities option. All jobs
shall be run in their own process groups. Immediately
before the shell issues a prompt after completion of the
background job, a message reporting the exit status of the
background job shall be written to standard error. If a
foreground job stops, the shell shall write a message to
standard error to that effect, formatted as described by
the jobs utility. In addition, if a job changes status
other than exiting (for example, if it stops for input or
output or is stopped by a SIGSTOP signal), the shell shall
write a similar message immediately prior to writing the
next prompt. This option is enabled by default for
interactive shells.
-n The shell shall read commands but does not execute them;
this can be used to check for shell script syntax errors.
An interactive shell may ignore this option.
-o Write the current settings of the options to standard
output in an unspecified format.
+o Write the current option settings to standard output in a
format that is suitable for reinput to the shell as
commands that achieve the same options settings.
-o option
This option is supported if the system supports the User
Portability Utilities option. It shall set various options,
many of which shall be equivalent to the single option
letters. The following values of option shall be supported:
allexport Equivalent to -a.
errexit Equivalent to -e.
ignoreeof Prevent an interactive shell from exiting on end-
of-file. This setting prevents accidental logouts
when <control>‐D is entered. A user shall
explicitly exit to leave the interactive shell.
monitor Equivalent to -m. This option is supported if
the system supports the User Portability
Utilities option.
noclobber Equivalent to -C (uppercase C).
noglob Equivalent to -f.
noexec Equivalent to -n.
nolog Prevent the entry of function definitions into
the command history; see Command History List.
notify Equivalent to -b.
nounset Equivalent to -u.
verbose Equivalent to -v.
vi Allow shell command line editing using the built-
in vi editor. Enabling vi mode shall disable any
other command line editing mode provided as an
implementation extension.
It need not be possible to set vi mode on for
certain block-mode terminals.
xtrace Equivalent to -x.
-u When the shell tries to expand an unset parameter other
than the '@' and '*' special parameters, it shall write a
message to standard error and the expansion shall fail with
the consequences specified in Section 2.8.1, Consequences
of Shell Errors.
-v The shell shall write its input to standard error as it is
read.
-x The shell shall write to standard error a trace for each
command after it expands the command and before it executes
it. It is unspecified whether the command that turns
tracing off is traced.
The default for all these options shall be off (unset) unless
stated otherwise in the description of the option or unless the
shell was invoked with them on; see sh.
The remaining arguments shall be assigned in order to the
positional parameters. The special parameter '#' shall be set to
reflect the number of positional parameters. All positional
parameters shall be unset before any new values are assigned.
If the first argument is '-', the results are unspecified.
The special argument "--" immediately following the set command
name can be used to delimit the arguments if the first argument
begins with '+' or '-', or to prevent inadvertent listing of all
shell variables when there are no arguments. The command set --
without argument shall unset all positional parameters and set
the special parameter '#' to zero.
