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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,    Internationalization
              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 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
              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-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
       suspended jobs. In the following examples:

              ... | xargs bg
              (bg)

       each bg operates in a different environment  and  does  not  share  its
       parent  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
       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
       IEEE Std 1003.1-2001  to  maintain 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 .