What can you do with the trap command in Bash?
The most common use of the trap command though is to trap the bash-generated psuedo-signal named EXIT. Say, for example, that you have a script that creates a temporary file.
How does the sudo trap work in Bash?
Inside the loop, the if-statement checks to see if the line is a sudo command. If so, it increments a counter. The code before the loop sets a trap for the SIGUSR1 signal, and when it’s received, the “show_opens” functions prints out the number of sudo commands seen since the script was started.
What does the exit signal do in Bash?
There are also “user” events available that are never generated by the system that you can generate to signal your script. Bash also provides a psuedo-signal called “EXIT”, which is executed when your script exits; this can be used to make sure that your script executes some cleanup on exit.
Can you trap a psuedo signal in Bash?
Although, as you’ll see, this is less useful than one might hope. The “SIGUSR1” signal is a “user”-defined signal that you can use however you like. it is never generated by the system. The most common use of the trap command though is to trap the bash-generated psuedo-signal named EXIT.
When to call exit trap handler in Bash?
If is called from the RETURN signal trap handler, then the EXIT trap handler will be called after all the RETURN signal trap handlers in the bash process. If is called from the EXIT signal trap handler, then the EXIT trap handler will change the exit code after the last EXIT signal trap handler is invoked.
When to use return signal trap in Bash?
The RETURN signal trap can support other signal traps to achieve the RAII pattern as in other languages. For example, to temporary disable interruption handling and auto restore it at the end of a function while an initialization code is executing. Protection from call not from a function context in case of the RETURN signal trap.
Can you run multiple traps on the same signal?
About the best you could do is run multiple commands from a single trap for a given signal, but you cannot have multiple concurrent traps for a single signal. For example: The first line sets a trap on signal 2 (SIGINT).