set man page on Archlinux

Man page or keyword search:  
man Server   11224 pages
apropos Keyword Search (all sections)
Output format
Archlinux logo
[printable version]

SET(1P)			   POSIX Programmer's Manual		       SET(1P)

       This  manual  page is part of the POSIX Programmer's Manual.  The Linux
       implementation of this interface may differ (consult the	 corresponding
       Linux  manual page for details of Linux behavior), or the interface may
       not be implemented on Linux.

       setset or unset options and positional parameters

       set [−abCefhmnuvx] [−o option] [argument...]

       set [+abCefhmnuvx] [+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 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

       The  set	 special built-in shall support the Base Definitions volume of
       POSIX.1‐2008, 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 speci‐

       Implementations shall support the options in the following list in both
       their <hyphen> and <plus-sign> forms. These options can also be	speci‐
       fied 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.1‐2008,  Section  4.22,  Variable
	     Assignment.  If the assignment precedes a utility name in a  com‐
	     mand,  the export attribute shall not persist in the current exe‐
	     cution environment after the utility completes, with  the	excep‐
	     tion  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.

			 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 prefix‐
			 ing 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,	 Exam‐
	     ples.  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,	 Redi‐
	     recting  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 immedi‐
	     ately shall exit 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  sub‐
		 shell	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  sub‐
	     shell 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 func‐
	     tions 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 Porta‐
	     bility Utilities option. It shall set various  options,  many  of
	     which  shall be equivalent to the single option letters. The fol‐
	     lowing 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 sys‐
		       tem 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 com‐
		       mand 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  com‐
		       mand  line  editing  mode provided as an implementation

		       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 stan‐
	     dard  error  and  shall  not  execute  the command containing the
	     expansion, but for the  purposes  of  setting  the	 '?'   special
	     parameter	and  the exit status of the shell the command shall be
	     treated as having been executed and returned an  exit  status  of
	     between  1 and 125 inclusive. A non-interactive shell shall imme‐
	     diately 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 num‐
       ber 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

       See the DESCRIPTION.

       See the DESCRIPTION.

       Not used.




       See the DESCRIPTION.

       The standard error shall be used only for diagnostic messages.





       The following sections are informative.

       Application writers should avoid relying on set	−e  within  functions.
       For example, in the following script:

	   set -e
	   start() {
	       echo some_server started successfully
	   start || echo >&2 some_server failed

       the  −e	setting is ignored within the function body (because the func‐
       tion is a command in an AND-OR list other than the last). Therefore, if
       some_server fails, the function carries on to echo "some_serverstarted‐
       successfully", and the exit status of the function is zero (which means
       "some_serverfailed" is not output).

       Write out all variables and their values:


       Set $1, $2, and $3 and set "$#" to 3:

	   set c a b

       Turn on the −x and −v options:

	   set −xv

       Unset all positional parameters:

	   set −−

       Set $1 to the value of x, even if it begins with '−' or '+':

	   set −− "$x"

       Set  the positional parameters to the expansion of x, even if x expands
       with a leading '−' or '+':

	   set −− $x

       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	delib‐
       erately; if it were issued as, for example:

	   set −− "$@"

       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  his‐
       torical	"$−"  paradigm would not be broken; see Section 2.5.2, Special

       The description of the −e option is intended to match the  behavior  of
       the 1988 version of the KornShell.

       The −h flag is related to command name hashing. See hash.

       The  following  set flags were omitted intentionally with the following

       −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,	virtu‐
	     ally precluding writing any compilers. To explain the behavior of
	     −k, it is necessary to describe the parsing algorithm,  which  is
	     implementation-defined. For example:

		 set −k; echo name=value


		 set −k
		 echo name=value

	     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 behav‐
	     ior  with	ksh  and  sh  differs. The reference page says that it
	     exits after reading and executing one command. What is  one  com‐
	     mand?  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 syn‐
       tax. 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

       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:

	   trap "jobs −n" CLD

       The  C shell provides two different levels of an asynchronous notifica‐
       tion 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:

	   notify [%job ... ]

       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 Korn‐
       Shell extensions to trap, nor the C shell notify	 environment  variable
       seemed  appropriate  (notify is not a proper POSIX environment variable

       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.

       Historically,  some  shells  applied  the  −u  option to all parameters
       including $@ and $*.  The standard developers felt that this was a mis‐
       feature since it is normal and common for $@ and $* to be used in shell
       scripts regardless of whether they were passed any arguments.  Treating
       these  uses  as an error when no arguments are passed reduces the value
       of −u for its intended purpose of finding spelling mistakes in variable
       names and uses of unset positional parameters.


       Section 2.14, Special Built-In Utilities, hash

       The  Base  Definitions  volume  of POSIX.1‐2008, Section 4.22, Variable
       Assignment, Section 12.2, Utility Syntax Guidelines

       Portions of this text are reprinted and reproduced in  electronic  form
       from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
       -- Portable Operating System Interface (POSIX),	The  Open  Group  Base
       Specifications Issue 7, Copyright (C) 2013 by the Institute of Electri‐
       cal and Electronics Engineers,  Inc  and	 The  Open  Group.   (This  is
       POSIX.1-2008  with  the	2013  Technical Corrigendum 1 applied.) 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 .

       Any  typographical  or  formatting  errors that appear in this page are
       most likely to have been introduced during the conversion of the source
       files  to  man page format. To report such errors, see https://www.ker‐ .

IEEE/The Open Group		     2013			       SET(1P)

List of man pages available for Archlinux

Copyright (c) for man pages and the logo by the respective OS vendor.

For those who want to learn more, the polarhome community provides shell access and support.

[legal] [privacy] [GNU] [policy] [cookies] [netiquette] [sponsors] [FAQ]
Polarhome, production since 1999.
Member of Polarhome portal.
Based on Fawad Halim's script.
Vote for polarhome
Free Shell Accounts :: the biggest list on the net