The trap builtin command

Synopsis

trap [-lp] [[ARGUMENT] SIGNAL]

Description

The trap command is used to "trap" signals and other events. In this context, "trapping" means to install handler code.

The shell code ARGUMENT is to be read and executed whenever the shell receives a signal or another event SIGNAL. The given SIGNAL specification can be

the name of a signal with the SIG prefix, e.g. SIGTERM
the name of a signal without the SIG prefix, e.g. TERM
the number of a signal (see trap -l), e.g. 15
the name or number of a special event (see table below), e.g. EXIT

Without any options or operands, trap prints a list of installed traps in a reusable format (equivalent to the -p option).

Special ARGUMENTs

if ARGUMENT is absent or - (dash), the signal/event handler is reset to its original value
if ARGUMENT is the null string, the signal/event is ignored

Special events

Name	Code	Description
`EXIT`	0	executed on shell exit
`DEBUG`		executed before every simple command
`RETURN`		executed when a shell function or a sourced code finishes executing
`ERR`		executed each time a command's failure would cause the shell to exit when the `-e` option (`errexit`) is enabled

Options

Option	Description
`-l`	print a list of signal names and their corresponding numbers
`-p`	display the trap commands associated with each signal specification in a reusable format

Return status

Status	Reason
0	no error/success
!=0	invalid option
!=0	invalid signal specification

Examples

List installed traps

trap

Ignore terminal interrupt (Ctrl-C, SIGINT)

trap '' INT

Portability considerations

trap is specified by POSIX(R) without the -l and -p options
in POSIX(R), beside signals, only EXIT (0) is valid as an event

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