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<H1> 9. Jobs & Signals </H1>
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<H2> 9.1 Jobs </H2>
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<A NAME="IDX100"></A>
If the <TT>MONITOR</TT> option is set,
an interactive shell associates a <EM>job</EM> with each pipeline.
It keeps a table of current jobs, printed by the <TT>jobs</TT>
command, and assigns them small integer numbers.
When a job is started asynchronously with `<TT>&</TT>',
the shell prints a line which looks like:
<P>
<TABLE><tr><td> </td><td class=example><pre>[1] 1234
</pre></td></tr></table><P>
indicating that the job which was started asynchronously was job number
1 and had one (top-level) process, whose process ID was 1234.
</P>
<P>
If a job is started with `<TT>&|</TT>' or `<TT>&!</TT>',
then that job is immediately disowned. After startup, it
does not have a place in the job table, and is not subject
to the job control features described here.
</P>
<P>
If you are running a job and wish to do something else you may hit the key
^Z (control-Z) which sends a <TT>TSTP</TT> signal to the current job: this key
may be redefined by the <TT>susp</TT> option of the external <TT>stty</TT> command.
<A NAME="IDX101"></A>
<A NAME="IDX102"></A>
The shell will then normally indicate that the job has been `suspended',
and print another prompt. You can then manipulate the state of this job,
<A NAME="IDX103"></A>
putting it in the background with the <TT>bg</TT> command, or run some other
commands and then eventually bring the job back into the foreground with
<A NAME="IDX104"></A>
the foreground command <TT>fg</TT>. A ^Z takes effect immediately and
is like an interrupt in that pending output and unread input are discarded
when it is typed.
</P>
<P>
A job being run in the background will suspend if it tries to read
from the terminal.
<A NAME="IDX105"></A>
<A NAME="IDX106"></A>
Background jobs are normally allowed to produce output,
but this can be disabled by giving the command `<TT>stty tostop</TT>'.
If you set this
tty option, then background jobs will suspend when they try to produce
output like they do when they try to read input.
</P>
<P>
When a command is suspended and continued later with the <TT>fg</TT> or
<TT>wait</TT> builtins, zsh restores tty modes that were in effect when it was
suspended. This (intentionally) does not apply if the command is
continued via `<TT>kill -CONT</TT>', nor when it is continued with <TT>bg</TT>.
</P>
<P>
<A NAME="IDX107"></A>
<A NAME="IDX108"></A>
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:
</P>
<P>
</P>
<DL COMPACT>
<DT><TT>%</TT><VAR>number</VAR>
<DD>The job with the given number.
<DT><TT>%</TT><VAR>string</VAR>
<DD>Any job whose command line begins with <VAR>string</VAR>.
<DT><TT>%?</TT><VAR>string</VAR>
<DD>Any job whose command line contains <VAR>string</VAR>.
<DT><TT>%%</TT>
<DD>Current job.
<DT><TT>%+</TT>
<DD>Equivalent to `<TT>%%</TT>'.
<DT><TT>%-</TT>
<DD>Previous job.
</DL>
<P>
The shell learns immediately whenever a process changes state.
<A NAME="IDX109"></A>
It normally informs you whenever a job becomes blocked so that
no further progress is possible. If the <TT>NOTIFY</TT> option is not set,
it waits until just before it prints a prompt before it informs you.
</P>
<P>
When the monitor mode is on, each background job that completes
triggers any trap set for <TT>CHLD</TT>.
</P>
<P>
When you try to leave the shell while jobs are running or suspended, you will
be warned that `You have suspended (running) jobs'.
You may use the <TT>jobs</TT> 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; the suspended
jobs will be terminated, and the running jobs will be sent
a <TT>SIGHUP</TT> signal, if the <TT>HUP</TT> option is set.
<A NAME="IDX110"></A>
</P>
<P>
<A NAME="IDX111"></A>
<A NAME="IDX112"></A>
<A NAME="IDX113"></A>
To avoid having the shell terminate the running jobs, either
use the <CITE>nohup</CITE> command (see man page nohup(1))
or the <TT>disown</TT> builtin.
</P>
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<H2> 9.2 Signals </H2>
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The <TT>INT</TT> and <TT>QUIT</TT> signals for an invoked
command are ignored if the command is followed by
`<TT>&</TT>' and the <TT>MONITOR</TT> option is not active.
Otherwise, signals have the values
inherited by the shell from its parent
(but see the <TT>TRAP</TT><VAR>NAL</VAR> special functions in <A HREF="zsh_8.html#SEC31">8. Functions</A>).
<A NAME="Arithmetic Evaluation"></A>
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