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73 lines
2.9 KiB
Markdown
73 lines
2.9 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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