linux man page for bg

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, 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
", <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  effec-
       tive  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 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 Technol-
       ogy -- 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)