CODEWITHSUNDEEP
linuxbashshellinterceptorprompt
Alfe
Alfe

Reputation: 59616

Can I react on entered command in bash?

I would like to configure my bash in a way so that I react on the event that the user enters a command. The moment they press Enter I would like my bash to run a script I installed first (analog to any PROMPT_COMMAND which is run each time a prompt is given out). This script should be able to

I have not found a proper way to do this. My current implementations are all flawed and use things like debug traps to intervene before executing a command or (HISTTIMEFORMAT='%s '; history 1) to ask the history after the command execution is complete about things when the command was started etc (but that is only hindsight which is not really what I want).

I'd expect something like a COMMAND_INTERCEPTION variable which would work similar to PROMPT_COMMAND but I'm not able to find anything like it.

I also considered to use command line completion to achieve my goal but wasn't able to find anything about reacting on sending a finished command in this, but maybe I just didn't find it.

Any help appreciated :)

Upvotes: 1

Views: 384

Answers (1)

ilkkachu
ilkkachu

Reputation: 6537

You can use the DEBUG trap and the extdebug feature, and peek into BASH_COMMAND from the trap handler to see the running command. (Though as noted in comments, the debug trap is sprung on every simple command, not every command line. Also subshells elude it.)

The debug handler can prevent the command from running, but can't change it directly. Though of course you could run any command inside the debugger, possibly using BASH_COMMAND and eval to build it and then tell the shell to ignore the original command.

This would prevent running anything starting with ls:

$ preventls() { case "$BASH_COMMAND" in ls*) echo "no!"; return 1 ;; esac; }
$ shopt -s extdebug
$ trap preventls DEBUG
$ ls -l
no!

Use trap - DEBUG to remove the trap. Tested on Bash 4.3.30.

Upvotes: 1

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