mirror of
https://github.com/flokoe/bash-hackers-wiki.git
synced 2024-11-25 07:43:42 +01:00
63 lines
2.2 KiB
Plaintext
63 lines
2.2 KiB
Plaintext
====== The trap builtin command ======
|
|
|
|
===== Synopsis =====
|
|
<code>trap [-lp] [[ARGUMENT] SIGNAL]</code>
|
|
|
|
===== 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 ''ARGUMENT''s
|
|
* 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 [[commands:builtin:set|''-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 ====
|
|
|
|
<code>
|
|
trap
|
|
</code>
|
|
|
|
==== Ignore terminal interrupt (Ctrl-C, SIGINT) ====
|
|
|
|
<code>
|
|
trap '' INT
|
|
</code>
|
|
|
|
===== 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
|
|
|
|
===== See also =====
|
|
|
|
* [[commands:builtin:set|the set command]] for the ''-e'' (''errexit'') option
|