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 .