Jobs


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Jobs
The 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 suspend
key (usually `^Z'),
which sends a STOP signal to the current job. The shell will then normally
indicate that the job has been `Suspended' and print another prompt.
If the listjobs shell variable is set, all jobs will be listed
like the jobs builtin command; if it is set to `long' the listing will
be in long format, like `jobs -l'.
You can then manipulate the state of the suspended job.
You can put it in the
``background'' with the bg command or run some other commands and
eventually bring the job back into the ``foreground'' with fg.
(See also the run-fg-editor editor command.)
A `^Z' takes effect immediately and is like an interrupt
in that pending output and unread input are discarded when it is typed.
The wait builtin command causes the shell to wait for all background
jobs to complete.

The `^]' key sends a delayed suspend signal, which does not generate a STOP
signal until a program attempts to read(2) it, to the current job.
This can usefully be typed ahead when you have prepared some commands for a
job which you wish to stop after it has read them.
The `^Y' key performs this function in csh(1); in tcsh,
`^Y' is an editing command. (+)

A job being run in the background stops if it tries to read from the
terminal. Background jobs are normally allowed to produce output, but this can
be disabled by giving the command `stty tostop'. If you set this tty option,
then background jobs will stop when they try to produce output like they do
when they try to read input.

There are several ways to refer to jobs in the shell. The character `%'
introduces a job name. If you wish to refer to job number 1, you can name it
as `%1'. Just naming a job brings it to the foreground; thus `%1' is a synonym
for `fg %1', bringing job 1 back into the foreground. Similarly, saying `%1 &'
resumes job 1 in the background, just like `bg %1'. A job can also be named
by an unambiguous prefix of the string typed in to start it: `%ex' would
normally restart a suspended ex(1) job, if there were only one suspended
job whose name began with the string `ex'. It is also possible to say
`%?string' to specify a job whose text contains string, if there
is only one such job.

The shell maintains a notion of the current and previous jobs. In output
pertaining to jobs, the current job is marked with a `+' and the previous job
with a `-'. The abbreviations `%+', `%', and (by analogy with the syntax of
the history mechanism) `%%' all refer to the current job, and `%-' refers
to the previous job.

The job control mechanism requires that the stty(1) option `new' be set
on some systems. It is an artifact from a `new' implementation of the tty
driver which allows generation of interrupt characters from the keyboard to
tell jobs to stop. See stty(1) and the setty builtin command for
details on setting options in the new tty driver.

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