bg

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.

              "[%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
       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(P)