Job Control Builtins

Job Control Builtins#

bg

bg

bg [jobspec …]

Resume each suspended job \<jobspec> in the background, as if it had been started with ‘&’. If \<jobspec> is not supplied, the shell uses its notion of the current job. bg returns zero unless it is run when job control is not enabled, or, when run with job control enabled, any \<jobspec> was not found or specifies a job that was started without job control.

fg

fg

fg [jobspec]

Resume the job \<jobspec> in the foreground and make it the current job. If \<jobspec> is not supplied, fg resumes the current job. The return status is that of the command placed into the foreground, or non-zero if run when job control is disabled or, when run with job control enabled, \<jobspec> does not specify a valid job or \<jobspec> specifies a job that was started without job control.

jobs

jobs

jobs [-lnprs] [jobspec]
jobs -x command [arguments]

The first form lists the active jobs. The options have the following meanings:

-l
List process IDs in addition to the normal information.

-n
Display information only about jobs that have changed status since the user was last notified of their status.

-p
List only the process ID of the job’s process group leader.

-r
Display only running jobs.

-s
Display only stopped jobs.

If \<jobspec> is supplied, jobs restricts output to information about that job. If \<jobspec> is not supplied, jobs lists the status of all jobs. The return status is zero unless an invalid option is encountered or an invalid \<jobspec> is supplied.

If the -x option is supplied, jobs replaces any \<jobspec> found in \<command> or \<arguments> with the corresponding process group ID, and executes \<command>, passing it \<argument>s, returning its exit status.

kill

kill

kill [-s sigspec] [-n signum] [-sigspec] id […]
kill -l|-L [exit_status]

Send a signal specified by \<sigspec> or \<signum> to the processes named by each \<id>. Each \<id> may be a job specification \<jobspec> or process ID \<pid>. \<sigspec> is either a case-insensitive signal name such as SIGINT (with or without the SIG prefix) or a signal number; \<signum> is a signal number. If \<sigspec> and \<signum> are not present, kill sends SIGTERM.

The -l option lists the signal names. If any arguments are supplied when -l is supplied, kill lists the names of the signals corresponding to the arguments, and the return status is zero. \<exit_status> is a number specifying a signal number or the exit status of a process terminated by a signal; if it is supplied, kill prints the name of the signal that caused the process to terminate. kill assumes that process exit statuses are greater than 128; anything less than that is a signal number. The -L option is equivalent to -l.

The return status is zero if at least one signal was successfully sent, or non-zero if an error occurs or an invalid option is encountered.

wait

wait

wait [-fn] [-p varname] [id …]

Wait until the child process specified by each \<id> exits and return the exit status of the last \<id>. Each \<id> may be a process ID \<pid> or a job specification \<jobspec>; if a jobspec is supplied, wait waits for all processes in the job.

If no options or \<id>s are supplied, wait waits for all running background jobs and the last-executed process substitution, if its process id is the same as \<\$!>, and the return status is zero.

If the -n option is supplied, wait waits for any one of the \<id>s or, if no \<id>s are supplied, any job or process substitution, to complete and returns its exit status. If none of the supplied \<id>s is a child of the shell, or if no arguments are supplied and the shell has no unwaited-for children, the exit status is 127.

If the -p option is supplied, wait assigns the process or job identifier of the job for which the exit status is returned to the variable \<varname> named by the option argument. The variable, which cannot be readonly, will be unset initially, before any assignment. This is useful only when used with the -n option.

Supplying the -f option, when job control is enabled, forces wait to wait for each \<id> to terminate before returning its status, instead of returning when it changes status.

If none of the \<id>s specify one of the shell’s an active child processes, the return status is 127. If wait is interrupted by a signal, any \<varname> will remain unset, and the return status will be greater than 128, as described above (see Signals). Otherwise, the return status is the exit status of the last \<id>.

disown

disown

disown [-ar] [-h] [id …]

Without options, remove each \<id> from the table of active jobs. Each \<id> may be a job specification \<jobspec> or a process ID \<pid>; if \<id> is a \<pid>, disown uses the job containing \<pid> as \<jobspec>.

If the -h option is supplied, disown does not remove the jobs corresponding to each id from the jobs table, but rather marks them so the shell does not send SIGHUP to the job if the shell receives a SIGHUP.

If no \<id> is supplied, the -a option means to remove or mark all jobs; the -r option without an \<id> argument removes or marks running jobs. If no \<id> is supplied, and neither the -a nor the -r option is supplied, disown removes or marks the current job.

The return value is 0 unless an \<id> does not specify a valid job.

suspend

suspend

suspend [-f]

Suspend the execution of this shell until it receives a SIGCONT signal. A login shell, or a shell without job control enabled, cannot be suspended; the -f option will override this and force the suspension. The return status is 0 unless the shell is a login shell or job control is not enabled and -f is not supplied.

When job control is not active, the kill and wait builtins do not accept \<jobspec> arguments. They must be supplied process IDs.