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73 lines
2.0 KiB
Markdown
73 lines
2.0 KiB
Markdown
# 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.md) 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.md) for the `-e` (`errexit`)
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option
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