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63 lines
2.2 KiB
Plaintext
63 lines
2.2 KiB
Plaintext
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====== The trap builtin command ======
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===== Synopsis =====
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<code>trap [-lp] [[ARGUMENT] SIGNAL]</code>
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===== Description =====
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The ''trap'' command is used to "trap" signals and other events. In this context, "trapping" means to install handler code.
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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
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* the name of a signal with the SIG prefix, e.g. ''SIGTERM''
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* the name of a signal without the SIG prefix, e.g. ''TERM''
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* the number of a signal (see ''trap -l''), e.g. ''15''
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* the name or number of a special event (see table below), e.g. ''EXIT''
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Without any options or operands, ''trap'' prints a list of installed traps in a reusable format (equivalent to the ''-p'' option).
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Special ''ARGUMENT''s
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* if ''ARGUMENT'' is absent or ''-'' (dash), the signal/event handler is reset to its original value
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* if ''ARGUMENT'' is the null string, the signal/event is ignored
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Special events
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^Name ^Code ^Description ^
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|''EXIT'' |0 |executed on shell exit |
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|''DEBUG'' | |executed before every simple command |
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|''RETURN'' | |executed when a shell function or a sourced code finishes executing |
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|''ERR'' | |executed each time a command's failure would cause the shell to exit when the [[commands:builtin:set|''-e'' option (''errexit'')]] is enabled |
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==== Options ====
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^Option ^Description ^
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|''-l'' |print a list of signal names and their corresponding numbers |
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|''-p'' |display the trap commands associated with each signal specification in a reusable format |
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==== Return status ====
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^Status ^Reason ^
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|0 |no error/success |
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|!=0 |invalid option |
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|!=0 |invalid signal specification |
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===== Examples =====
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==== List installed traps ====
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<code>
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trap
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</code>
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==== Ignore terminal interrupt (Ctrl-C, SIGINT) ====
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<code>
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trap '' INT
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</code>
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===== Portability considerations =====
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* ''trap'' is specified by POSIX(R) without the ''-l'' and ''-p'' options
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* in POSIX(R), beside signals, only ''EXIT'' (0) is valid as an event
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===== See also =====
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* [[commands:builtin:set|the set command]] for the ''-e'' (''errexit'') option
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