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

PROLOG
       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.

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 util-
       ity 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,  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).

       LC_MESSAGES
              Determine the locale that should be used to  affect  the  format
              and contents of diagnostic 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 iden-
              tified 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-terminal 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
              (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.

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 char-
       acteristics  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 IEEE Std 1003.1-2001 to main-
       tain a degree of uniformity 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.

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 original Standard can be obtained online
       at http://www.opengroup.org/unix/online.html .

IEEE/The Open Group                  2003                               BG(1P)
 

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