BG(1P)

💖 BG(1P) — the POSIX Programmer's Manual, bestie edition 💖

okay so real quick before we dive in: this page lives in the POSIX Programmer's Manual, which is its whole ~thing~. Heads up though — the Linux implementation of this interface may be different from what's written here (so go check the matching Linux manual page for the deets on Linux behavior), or honestly the interface might not even be implemented on Linux at all. 🙈

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✨ PROLOG ✨

so yeah, like I just said: 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. That's the vibe check, moving on bestie 🫶

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🌸 NAME 🌸

bg — run jobs in the background. that's it, that's the whole name section. iconic behavior honestly.

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🎀 SYNOPSIS 🎀

bg [job_id...]

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🦋 DESCRIPTION 🦋

okay so here's the tea ☕ — if job control is enabled (peep the description of set -m for that), then the bg utility shall resume suspended jobs from the current environment by running them as background jobs. She's a resume button, basically. Main character energy.

If the job specified by job_id is already a running background job? Then bg shall have no effect and shall exit successfully. like okay we see you, already thriving, no notes 💅

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 Section 2.9.3.1, Examples for that whole situation.)

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💅 OPTIONS 💅

None. literally zero options, she's unbothered, she's minimal, she ate ✨

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👑 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. (default behavior, we love a fallback 💖) The format of job_id is described in the Base Definitions volume of POSIX.1‐2017, Section 3.204, Job Control Job ID.

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🍓 STDIN 🍓

Not used. she doesn't want your input, respectfully.

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🌈 INPUT FILES 🌈

None.

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🧚 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 POSIX.1‐2017, 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. she overrides. periodt.
• 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.

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⭐ ASYNCHRONOUS EVENTS ⭐

Default. no drama here.

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💜 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 '%'. so like %1 energy.
• command — The associated command that was given to the shell.

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😭 STDERR 😭

The standard error shall be used only for diagnostic messages. no random yapping on stderr please.

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🎀 OUTPUT FILES 🎀

None.

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🫶 EXTENDED DESCRIPTION 🫶

None. (yes queen, keep it simple)

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🔥 EXIT STATUS 🔥

The following exit values shall be returned:

1. 0 — Successful completion.
2. >0 — An error occurred.

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💀 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. like, nothing happens, sorry babe 😭

The following sections are informative.

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🌸 APPLICATION USAGE 🌸

A job is generally suspended by typing the SUSP character (<control>‐Z on most systems); see the Base Definitions volume of POSIX.1‐2017, 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. (iykyk)

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

Now, the important part bestie: 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. so like, don't pipe it, she won't know what you're talking about 💀

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🌈 EXAMPLES 🌈

None.

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⭐ RATIONALE ⭐

The extensions to the shell specified in this volume of POSIX.1‐2017 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.1‐2017 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. so she's polite about your terminal width, we stan.

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🦋 FUTURE DIRECTIONS 🦋

None.

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💖 SEE ALSO 💖

• Section 2.9.3.1, Examples
• fg
• kill
• jobs
• wait
• The Base Definitions volume of POSIX.1‐2017, Section 3.204, Job Control Job ID
• The Base Definitions volume of POSIX.1‐2017, Chapter 8, Environment Variables
• The Base Definitions volume of POSIX.1‐2017, Chapter 11, General Terminal Interface

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👑 COPYRIGHT 👑

Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1-2017, Standard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 7, 2018 Edition, Copyright (C) 2018 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 .

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.kernel.org/doc/man-pages/reporting_bugs.html .

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and that's the whole page bestie!! brought to you by IEEE/The Open Group, dated 2017, for BG(1P) — go run your jobs in the background and slay 💅✨🫶