When Job Control is enabled, the Bourne shell built-in jobs reports all jobs that are stopped or executing in the background. If %job_id is omitted, all jobs that are stopped or running in the background will be reported. The following options will modify/enhance the output of jobs:

-l

Reports the process group ID and working directory of the jobs.

-p

Reports only the process group ID of the jobs.

-x

Replaces any job_id found in command or arguments with the corresponding process group ID, and then executes command passing it arguments.

When the shell is invoked as jsh, Job Control is enabled in addition to all of the functionality described previously for sh. Typically Job Control is enabled for the interactive shell only. Non-interactive shells typically do not benefit from the added functionality of Job Control.

With Job Control enabled every command or pipeline the user enters at the terminal is called a job_id. All jobs exist in one of the following states: foreground, background or stopped. These terms are defined as follows:

1. A job in the foreground has read and write access to the controlling terminal.
2. A job in the background is denied read access and has conditional write access to the controlling terminal (see stty(1))
3. A stopped job is a job that has been placed in a suspended state, usually as a result of a SIGTSTP signal (see signal(3HEAD)).

Every job that the shell starts is assigned a positive integer, called a job_id number which is tracked by the shell and will be used as an identifier to indicate a specific job. Additionally, the shell keeps track of the current and previous jobs. The current job is the most recent job to be started or restarted. The previous job is the first non-current job.

The acceptable syntax for a Job Identifier is of the form:

%job_id

where job_id may be specified in any of the following formats:

% or +

for the current job

-

for the previous job

?<string>

specify the job for which the command line uniquely contains string.

n

for job number n, where n is a job number

pref

where pref is a unique prefix of the command name (for example, if the command ls -l name were running in the background, it could be referred to as %ls); pref cannot contain blanks unless it is quoted.

When Job Control is enabled, fg resumes the execution of a stopped job in the foreground, also moves an executing background job into the foreground. If %job_id is omitted the current job is assumed.

When Job Control is enabled, bg resumes the execution of a stopped job in the background. If %job_id is omitted the current job is assumed.

stop stops the execution of a background job(s) by using its job_id, or of any process by using its pid; see ps(1).

The C shell built-in, jobs, without an argument, lists the active jobs under job control.

-l

List process IDs, in addition to the normal information.

The shell associates a numbered job_id with each command sequence to keep track of those commands that are running in the background or have been stopped with TSTP signals (typically Control-Z). When a command or command sequence (semicolon-separated list) is started in the background using the & metacharacter, the shell displays a line with the job number in brackets and a list of associated process numbers:

[1] 1234

To see the current list of jobs, use the jobs built-in command. The job most recently stopped (or put into the background if none are stopped) is referred to as the current job and is indicated with a `+'. The previous job is indicated with a `-'; when the current job is terminated or moved to the foreground, this job takes its place (becomes the new current job).

To manipulate jobs, refer to the bg, fg, kill, stop, and % built-in commands.

A reference to a job begins with a `%'. By itself, the percent sign refers to the current job.

% %+ %%

The current job.

%-

The previous job.

%j

Refer to job j as in: `kill -9 %j'. j can be a job number, or a string that uniquely specifies the command line by which it was started; `fg %vi' might bring a stopped vi job to the foreground, for instance.

%?string

Specify the job for which the command line uniquely contains string.

A job running in the background stops when it attempts to read from the terminal. Background jobs can normally produce output, but this can be suppressed using the `stty tostop' command.

fg brings the current or specified job_id into the foreground.

bg runs the current or specified jobs in the background.

stop stops the execution of a background job(s) by using its job_id, or of any process by using its pid; see ps(1).

notify will notify the user asynchronously when the status of the current job or specified jobs changes.

jobs displays the status of the jobs that were started in the current shell environment. When jobs reports the termination status of a job, the shell removes its process ID from the list of those "known in the current shell execution environment."

job_id specifies the jobs for which the status is to be displayed. If no job_id is given, the status information for all jobs will be displayed.

The following options will modify/enhance the output of jobs:

-l

(The letter ell.) Provides more information about each job listed. This information includes the job number, current job, process group ID, state and the command that formed the job.

-n

Displays only jobs that have stopped or exited since last notified.

-p

Displays only the process IDs for the process group leaders of the selected jobs.

By default, jobs displays the status of all the stopped jobs, running background jobs, and all jobs whose status has changed and have not been reported by the shell.

If the monitor option of the set command is turned on, an interactive shell associates a job with each pipeline. It keeps a table of current jobs, printed by the jobs command, and assigns them small integer numbers. When a job is started asynchronously with &, the shell prints a line which looks like:

[1] 1234

indicating that the job, which was started asynchronously, was job number 1 and had one (top-level) process, whose process id was 1234.

If you are running a job and wish to do something else you may hit the key ^Z (Control-Z) which sends a STOP signal to the current job. The shell will then normally indicate that the job has been "Stopped" (see OUTPUT below), and print another prompt. You can then manipulate the state of this job, putting it in the background with the bg command, or run some other commands and then eventually bring the job back into the foreground with the foreground command fg. A ^Z takes effect immediately and is like an interrupt, in that pending output and unread input are discarded when it is typed.

There are several ways to refer to jobs in the shell. A job can be referred to by the process id of any process of the job or by one of the following:

%number

The job with the given number.

%string

Any job whose command line begins with string; works only in the interactive mode when the history file is active.

%?string

Any job whose command line contains string; works only in the interactive mode when the history file is active.

%%

Current job.

%+

Equivalent to %%.

%-

Previous job.

The shell learns immediately whenever a process changes state. It normally informs you whenever a job becomes blocked so that no further progress is possible, but only just before it prints a prompt. This is done so that it does not otherwise disturb your work. When the monitor mode is on, each background job that completes triggers any trap set for CHLD. When you try to leave the shell while jobs are running or stopped, you will be warned that `You have stopped (running) jobs.' You may use the jobs command to see what they are. If you do this or immediately try to exit again, the shell will not warn you a second time, and the stopped jobs will be terminated.

fg will move a background job from the current environment into the foreground. Using fg to place a job in the foreground will remove its process ID from the list of those "known in the current shell execution environment." The fg command is available only on systems that support job control. If job_id is not specified, the current job is brought into the foreground.

bg resumes suspended jobs from the current environment by running them as background jobs. If the job specified by job_id is already a running background job, bg has no effect and will exit successfully. Using bg to place a job into the background causes its process ID to become ``known in the current shell execution environment'', as if it had been started as an asynchronous list. The bg command is available only on systems that support job control. If job_id is not specified, the current job is placed in the background.

stop stops the execution of a background job(s) by using its job_id, or of any process by using its pid. See ps(1).