Editing Bash (Unix shell) (section)

=== Process Management (a.k.a., "Job control") ===
The Bash shell has two modes of execution for commands: batch (asynchronous), and concurrent (synchronous).

To execute commands in batch mode (i.e., in sequence) they must be separated by the character ";", or on separate lines:

<syntaxhighlight lang="bash">
command1; command2
command3
</syntaxhighlight>

In this example, when command1 is finished, command2 is executed, and when command2 has completed, command3 will execute.

A [[Background process|background execution]] of command1 can occur using (symbol &) at the end of an execution command, and process will be executed in background while immediately returning control to the shell and allowing continued execution of commands.
<syntaxhighlight lang="bash">command1 &</syntaxhighlight>

Or to have a concurrent execution of command1 and command2, they must be executed in the Bash shell in the following way:

<syntaxhighlight lang="bash">
command1 & command2
</syntaxhighlight>

In this case command1 is executed in the background ''&'' symbol, returning immediately control to the shell that executes command2 in the foreground.

A process can be stopped and control returned to bash by typing {{Key press|Ctrl|z}} while the process is running in the foreground.<ref>{{Cite web |title=Bash Reference Manual     |url=https://www.gnu.org/software/bash/manual/bash.html#index-background     |url-status=live     |archive-url=https://web.archive.org/web/20180315115230/http://www.gnu.org/software/bash/manual/bash.html#index-background     |archive-date=March 15, 2018     |access-date=March 27, 2018     |publisher=[[GNU Project]]  }}</ref>

A list of all processes, both in the background and stopped, can be achieved by running <code>jobs</code>:
<syntaxhighlight lang="console">
$ jobs
[1]-  Running                  command1 &
[2]+  Stopped                  command2
</syntaxhighlight>

In the output, the number in brackets refers to the job id. The plus sign signifies the default process for <code>bg</code> and <code>fg</code>. The text "Running" and "Stopped" refer to the [[process state]]. The last string is the command that started the process.

The state of a process can be changed using various commands. The <code>fg</code> command brings a process to the foreground, while <code>bg</code> sets a stopped process running in the background. <code>bg</code> and <code>fg</code> can take a job id as their first argument, to specify the process to act on. Without one, they use the default process, identified by a plus sign in the output of <code>jobs</code>. The <code>[[Kill (command)|kill]]</code> command can be used to end a process prematurely, by sending it a [[Signal (IPC)|signal]]. The job id must be specified after a percent sign:

<syntaxhighlight lang="bash">
kill %1
</syntaxhighlight>