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73 lines
2.3 KiB
Markdown
73 lines
2.3 KiB
Markdown
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# The trap builtin command
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## Synopsis
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trap [-lp] [[ARGUMENT] SIGNAL]
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## Description
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The `trap` command is used to \"trap\" signals and other events. In this
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context, \"trapping\" means to install handler code.
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The shell code `ARGUMENT` is to be read and executed whenever the shell
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receives a signal or another event `SIGNAL`. The given `SIGNAL`
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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
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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
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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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---------- ------ --------------------------------------------------------------------------------------------------------------------------------------------
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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 [`-e` option (`errexit`)](/commands/builtin/set) is enabled
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### Options
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Option Description
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-------- ------------------------------------------------------------------------------------------
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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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-------- ------------------------------
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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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trap
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### Ignore terminal interrupt (Ctrl-C, SIGINT)
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trap '' INT
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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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- [the set command](/commands/builtin/set) for the `-e` (`errexit`)
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option
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