Originální popis anglicky:
set - set or unset options and positional parameters
Návod, kniha: POSIX Programmer's Manual
set [-abCefmnuvx][-h][-o
option ][argument...]
set
[+abCefmnuvx][+h
][+o
option][argument...]
set --
[argument...]
set -o
set +o
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
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
IEEE Std 1003.1-2001, Section 12.2, Utility Syntax Guidelines
except that options can be specified with either a leading hyphen (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 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 IEEE Std 1003.1-2001, Section 4.21,
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
Asynchronous Lists . Asynchronous notification shall
not be enabled by default.
- -C
- (Uppercase C.) Prevent existing files from being
overwritten by the shell's '>' redirection operator (see
Redirecting Output ); the ">|" redirection
operator shall override this noclobber option for an individual
file.
- -e
- When this option is on, if a simple command fails for any
of the reasons listed in Consequences of Shell Errors or returns an
exit status value >0, and is not part of the compound list following a
while, until, or if keyword, and is not a part of an
AND or OR list, and is not a pipeline preceded by the ! reserved
word, then the shell shall immediately exit.
- -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
- The shell shall write a message to standard error when it
tries to expand a variable that is not set and immediately exit. An
interactive shell shall not exit.
- -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.
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.
See the DESCRIPTION.
See the DESCRIPTION.
Not used.
None.
None.
Default.
See the DESCRIPTION.
The standard error shall be used only for diagnostic messages.
None.
None.
Zero.
Default.
The following sections are informative.
None.
Write out all variables and their values:
Set $1, $2, and $3 and set
"$#" to 3:
Turn on the
-x and
-v options:
Unset all positional parameters:
Set $1 to the value of
x, even if it begins with
'-' or
'+'
:
Set the positional parameters to the expansion of
x, even if
x
expands with a leading
'-' or
'+' :
The
set -- form is listed specifically in the SYNOPSIS even though this
usage is implied by the Utility Syntax Guidelines. The explanation of this
feature removes any ambiguity about whether the
set -- form might be
misinterpreted as being equivalent to
set without any options or
arguments. The functionality of this form has been adopted from the KornShell.
In System V,
set -- only unsets parameters if there is at least one
argument; the only way to unset all parameters is to use
shift. Using
the KornShell version should not affect System V scripts because there should
be no reason to issue it without arguments deliberately; if it were issued as,
for example:
and there were in fact no arguments resulting from
"$@" ,
unsetting the parameters would have no result.
The
set + form in early proposals was omitted as being an unnecessary
duplication of
set alone and not widespread historical practice.
The
noclobber option was changed to allow
set -C as well as
the
set -o noclobber option. The single-letter version
was added so that the historical
"$-" paradigm would not be
broken; see
Special Parameters .
The
-h flag is related to command name hashing and is only required on
XSI-conformant systems.
The following
set flags were omitted intentionally with the following
rationale:
- -k
- The -k flag was originally added by the author of
the Bourne shell to make it easier for users of pre-release versions of
the shell. In early versions of the Bourne shell the construct set
name= value had to be used to assign values to shell
variables. The problem with -k is that the behavior affects
parsing, virtually precluding writing any compilers. To explain the
behavior of -k, it is necessary to describe the parsing algorithm,
which is implementation-defined. For example:
and:
behave differently. The interaction with functions is even more complex. What is
more, the
-k flag is never needed, since the command line could have
been reordered.
- -t
- The -t flag is hard to specify and almost never
used. The only known use could be done with here-documents. Moreover, the
behavior with ksh and sh differs. The reference page says
that it exits after reading and executing one command. What is one
command? If the input is date; date, sh executes both
date commands while ksh does only the first.
Consideration was given to rewriting
set to simplify its confusing
syntax. A specific suggestion was that the
unset utility should be used
to unset options instead of using the non-
getopt() -able +
option syntax. However, the conclusion was reached that the historical
practice of using +
option was satisfactory and that there was no
compelling reason to modify such widespread historical practice.
The
-o option was adopted from the KornShell to address user needs. In
addition to its generally friendly interface,
-o is needed to provide
the
vi command line editing mode, for which historical practice yields
no single-letter option name. (Although it might have been possible to invent
such a letter, it was recognized that other editing modes would be developed
and
-o provides ample name space for describing such extensions.)
Historical implementations are inconsistent in the format used for
-o
option status reporting. The
+o format without an option-argument was
added to allow portable access to the options that can be saved and then later
restored using, for instance, a dot script.
Historically,
sh did trace the command
set +x, but
ksh did not.
The
ignoreeof setting prevents accidental logouts when the end-of-file
character (typically <control>-D) is entered. A user shall explicitly
exit to leave the interactive shell.
The
set -m option was added to apply only to the UPE because it
applies primarily to interactive use, not shell script applications.
The ability to do asynchronous notification became available in the 1988 version
of the KornShell. To have it occur, the user had to issue the command:
The C shell provides two different levels of an asynchronous notification
capability. The environment variable
notify is analogous to what is
done in
set -b or
set -o notify. When set,
it notifies the user immediately of background job completions. When unset,
this capability is turned off.
The other notification ability comes through the built-in utility
notify.
The syntax is:
By issuing
notify with no operands, it causes the C shell to notify the
user asynchronously when the state of the current job changes. If given
operands,
notify asynchronously informs the user of changes in the
states of the specified jobs.
To add asynchronous notification to the POSIX shell, neither the KornShell
extensions to
trap, nor the C shell
notify environment variable
seemed appropriate (
notify is not a proper POSIX environment variable
name).
The
set -b option was selected as a compromise.
The
notify built-in was considered to have more functionality than was
required for simple asynchronous notification.
None.
Special Built-In Utilities
Portions of this text are reprinted and reproduced in electronic form from IEEE
Std 1003.1, 2003 Edition, Standard for Information Technology -- Portable
Operating System Interface (POSIX), The Open Group Base Specifications Issue
6, Copyright (C) 2001-2003 by the Institute of Electrical and Electronics
Engineers, Inc and The Open Group. In the event of any discrepancy between
this version and the original IEEE and The Open Group Standard, the original
IEEE and The Open Group Standard is the referee document. The original
Standard can be obtained online at http://www.opengroup.org/unix/online.html
.
