FG(1P) POSIX Programmer's Manual FG(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.
NAMEfg — run jobs in the foreground
SYNOPSISfg [job_id]
DESCRIPTION
If job control is enabled (see the description of set −m), the fg util‐
ity shall move a background job from the current environment (see Sec‐
tion 2.12, Shell Execution Environment) into the foreground.
Using fg to place a job into the foreground shall remove its process ID
from the list of those ``known in the current shell execution environ‐
ment''; see Section 2.9.3.1, Examples.
OPTIONS
None.
OPERANDS
The following operand shall be supported:
job_id Specify the job to be run as a foreground job. If no job_id
operand is given, the job_id for the job that was most
recently suspended, placed in the background, or run as a
background job shall be used. The format of job_id is
described in the Base Definitions volume of POSIX.1‐2008,
Section 3.204, Job Control Job ID.
STDIN
Not used.
INPUT FILES
None.
ENVIRONMENT VARIABLES
The following environment variables shall affect the execution of fg:
LANG Provide a default value for the internationalization vari‐
ables that are unset or null. (See the Base Definitions vol‐
ume of POSIX.1‐2008, 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 fg utility shall write the command line of the job to standard out‐
put in the following format:
"%s\n", <command>
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 fg utility shall exit with an error and
no job shall be placed in the foreground.
The following sections are informative.
APPLICATION USAGE
The fg utility does not work as expected when it is operating in its
own utility execution environment because that environment has no
applicable jobs to manipulate. See the APPLICATION USAGE section for
bg. For this reason, fg is generally implemented as a shell regular
built-in.
EXAMPLES
None.
RATIONALE
The extensions to the shell specified in this volume of POSIX.1‐2008
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 POSIX.1‐2008 to maintain a degree of uni‐
formity with the rest of the KornShell features selected (such as the
very popular command line editing features).
FUTURE DIRECTIONS
None.
SEE ALSO
Section 2.9.3.1, Examples, Section 2.12, Shell Execution Environment,
bg, kill, jobs, wait
The Base Definitions volume of POSIX.1‐2008, Section 3.204, Job Control
Job ID, Chapter 8, Environment Variables
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 7, Copyright (C) 2013 by the Institute of Electri‐
cal and Electronics Engineers, Inc and The Open Group. (This is
POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) 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.unix.org/online.html .
Any typographical or formatting errors that appear in this page are
most likely to have been introduced during the conversion of the source
files to man page format. To report such errors, see https://www.ker‐
nel.org/doc/man-pages/reporting_bugs.html .
IEEE/The Open Group 2013 FG(1P)
