Bash Using "trap" to react to signals and system events
Syntax
- trap action sigspec... # Run "action" on a list of signals
- trap sigspec... # Omitting action resets traps for signals
Parameters
| Parameter | Meaning |
|---|---|
| -p | List currently installed traps |
| -l | List signal names and corresponding numbers |
Remarks
The trap utility is a special shell built-in. It's defined in POSIX, but bash adds some useful extensions as well.
Examples that are POSIX-compatible start with #!/bin/sh, and examples that start with #!/bin/bash use a bash extension.
The signals can either be a signal number, a signal name (without the SIG prefix), or the special keyword EXIT.
Those guaranteed by POSIX are:
| Number | Name | Notes |
|---|---|---|
| 0 | EXIT | Always run on shell exit, regardless of exit code |
| 1 | SIGHUP | |
| 2 | SIGINT | This is what ^C sends |
| 3 | SIGQUIT | |
| 6 | SIGABRT | |
| 9 | SIGKILL | |
| 14 | SIGALRM | |
| 15 | SIGTERM | This is what kill sends by default |
