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

NAME
       bg - run jobs in the background

SYNOPSIS
       bg [job_id ...]

DESCRIPTION
       If  job	control  is  enabled (see the description of set -m), the bg utility shall resume
       suspended jobs from the current environment (see 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 Asynchronous Lists .

OPTIONS
       None.

OPERANDS
       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 IEEE Std 1003.1-2001, Section 3.203, Job Control Job
	      ID.

STDIN
       Not used.

INPUT FILES
       None.

ENVIRONMENT VARIABLES
       The following environment variables shall affect the execution of bg:

       LANG   Provide  a  default  value for the internationalization variables that are unset or
	      null. (See the Base Definitions volume of IEEE Std 1003.1-2001, Section 8.2, Inter-
	      nationalization Variables 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  interna-
	      tionalization 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  argu-
	      ments).

       LC_MESSAGES
	      Determine the locale that should be used to affect the format and contents of diag-
	      nostic messages written to standard error.

       NLSPATH
	      Determine the location of message catalogs for the processing of LC_MESSAGES .

ASYNCHRONOUS EVENTS
       Default.

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

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

       where the fields are as follows:

       <job-number>
	      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.

STDERR
       The standard error shall be used only for diagnostic messages.

OUTPUT FILES
       None.

EXTENDED DESCRIPTION
       None.

EXIT STATUS
       The following exit values shall be returned:

	0     Successful completion.

       >0     An error occurred.

CONSEQUENCES OF ERRORS
       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.

APPLICATION USAGE
       A  job  is generally suspended by typing the SUSP character (<control>-Z on most systems);
       see the Base Definitions volume of  IEEE Std 1003.1-2001,  Chapter  11,	General  Terminal
       Interface.   At that point, bg can put the job into the background. This is most effective
       when the job is expecting no terminal input and its output has been redirected to non-ter-
       minal 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 suspended jobs. In the following examples:

	      ... | xargs bg
	      (bg)

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

EXAMPLES
       None.

RATIONALE
       The  extensions	to the shell specified in this volume of IEEE Std 1003.1-2001 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 charac-
       teristics 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 vol-
       ume of IEEE Std 1003.1-2001 to maintain a degree of uniformity with the rest of the  Korn-
       Shell 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.

FUTURE DIRECTIONS
       None.

SEE ALSO
       Asynchronous Lists , fg , kill() , jobs , wait()

COPYRIGHT
       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 orig-
       inal Standard can be obtained online at http://www.opengroup.org/unix/online.html .

IEEE/The Open Group			       2003					    BG(P)
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