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BG(1P)			   POSIX Programmer's Manual			BG(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.

       bg — run jobs in the background

       bg [job_id...]

       If job control is enabled (see the description of set −m), the bg util‐
       ity  shall resume suspended jobs from the current environment (see Sec‐
       tion 2.12, Shell Execution Environment) by running them	as  background
       jobs.  If  the  job specified by job_id is already a running background
       job, the bg utility shall have no effect and shall exit successfully.

       Using bg to place a job into the background shall cause its process  ID
       to  become  ``known in the current shell execution environment'', as if
       it had been started as an asynchronous list; see Section, Exam‐


       The following operand shall be supported:

       job_id	 Specify  the  job  to	be  resumed as a background job. If no
		 job_id operand is given,  the	most  recently	suspended  job
		 shall	be used. The format of job_id is described in the Base
		 Definitions volume of POSIX.1‐2008, Section 3.204,  Job  Con‐
		 trol Job ID.

       Not used.


       The following environment variables shall affect the execution of bg:

       LANG	 Provide  a  default  value for the internationalization vari‐
		 ables that are unset or null. (See the Base Definitions  vol‐
		 ume  of POSIX.1‐2008, Section 8.2, Internationalization Vari‐
		 ables for the precedence  of  internationalization  variables
		 used to determine the values of locale categories.)

       LC_ALL	 If  set  to  a non-empty string value, override the values of
		 all the other internationalization variables.

       LC_CTYPE	 Determine the locale for the interpretation of	 sequences  of
		 bytes of text data as characters (for example, single-byte as
		 opposed to multi-byte characters in arguments).

		 Determine the locale that should be used to affect the format
		 and  contents	of  diagnostic	messages  written  to standard

       NLSPATH	 Determine the location of message catalogs for the processing


       The output of bg shall consist of a line in the format:

	   "[%d] %s\n", <job-number>, <command>

       where the fields are as follows:

		 A  number  that  can be used to identify the job to the wait,
		 fg, and kill utilities. Using these utilities, the job can be
		 identified by prefixing the job number with '%'.

       <command> The associated command that was given to the shell.

       The standard error shall be used only for diagnostic messages.



       The following exit values shall be returned:

	0    Successful completion.

       >0    An error occurred.

       If job control is disabled, the bg utility shall exit with an error and
       no job shall be placed in the background.

       The following sections are informative.

       A job is generally suspended by typing the SUSP character  (<control>‐Z
       on  most	 systems);  see	 the  Base Definitions volume of POSIX.1‐2008,
       Chapter 11, General Terminal Interface.	At that point, bg can put  the
       job into the background. This is most effective when the job is expect‐
       ing no terminal input and its output has been redirected to  non-termi‐
       nal  files. A background job can be forced to stop when it has terminal
       output by issuing the command:

	   stty tostop

       A background job can be stopped with the command:

	   kill −s stop job ID

       The bg utility does not work as expected when it is  operating  in  its
       own  utility execution environment because that environment has no sus‐
       pended jobs. In the following examples:

	   ... | xargs bg

       each bg operates in a different environment and does not share its par‐
       ent  shell's  understanding  of	jobs. For this reason, bg is generally
       implemented as a shell regular built-in.


       The extensions to the shell specified in this  volume  of  POSIX.1‐2008
       have  mostly  been based on features provided by the KornShell. The job
       control features provided by bg, fg, and jobs are  also	based  on  the
       KornShell.  The standard developers examined the characteristics of the
       C shell versions of these utilities and found that  differences	exist.
       Despite	widespread  use	 of  the  C shell, the KornShell versions were
       selected for this volume of POSIX.1‐2008 to maintain a degree  of  uni‐
       formity	with  the rest of the KornShell features selected (such as the
       very popular command line editing features).

       The bg utility is expected to wrap its output if the output exceeds the
       number of display columns.


       Section, Examples, fg, kill, jobs, wait

       The Base Definitions volume of POSIX.1‐2008, Section 3.204, Job Control
       Job ID, Chapter 8, Environment Variables, Chapter 11, General  Terminal

       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				BG(1P)

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