capture all bash commands as parameters for a custom runner

Question

I have a custom 'runner'-script that I need to use to run all of my terminal commands. Below you can see the general idea in the script.

#!/usr/bin/env bash echo "Running '$@'" # do stuff before running cmd $@ echo "Done" # do stuff after running cmd

I can use the script in bash as follows:

$ ./run.sh echo test Running 'echo test' test Done $

I would like to use it like this:

$ echo test Running 'echo test' test Done $

Bash has the trap ... DEBUG and PROMPT_COMMAND, which lets me execute something before and after a command, but is there something that would allow me to execute instead of the command?

There is also the command_not_found_handle which would work if I had an empty PATH env variable, but that seems too dirty.

As an aside, you are missing obligatory quotes around "$@". Without the double quotes, your code is broken - it cannot handle quoted arguments correctly. — tripleee
– tripleee, Commented Mar 19, 2019 at 10:59
If the purpose of your script is to run arbitrary code, then this is the case where you should use eval. Just use eval "$1" instead of "$@", and run the script as ./run.sh 'echo test' instead. (And make sure that the string you pass to the script is properly quotes, e.g., ./run.sh 'echo "This is an asterisk: *"'. — chepner
– chepner, Commented Mar 19, 2019 at 11:23
Possible duplicate of detecting command not found in bash script — vfalcao
– vfalcao, Commented Mar 19, 2019 at 15:32

Al Hoo · Accepted Answer · 2019-03-20 11:55:00Z

After some digging, I ended up looking at the source code and found that bash does not support custom executors. Below is a patch to add a new handle that works similarly as the command_not_found_handler.

diff --git a/eval.c b/eval.c index f02d6e40..8d32fafa 100644 --- a/eval.c +++ b/eval.c @@ -52,6 +52,10 @@ extern sigset_t top_level_mask; #endif +#ifndef EXEC_HOOK +# define EXEC_HOOK "command_exec_handle" +#endif + static void send_pwd_to_eterm __P((void)); static sighandler alrm_catcher __P((int)); @@ -172,7 +176,15 @@ reader_loop () executing = 1; stdin_redir = 0; - execute_command (current_command); + SHELL_VAR *hookf = find_function (EXEC_HOOK); + if (hookf == 0) { + execute_command (current_command); + } else { + char *command_to_print = make_command_string (current_command); + WORD_LIST *og = make_word_list(make_word(command_to_print), (WORD_LIST *)NULL); + WORD_LIST *wl = make_word_list(make_word(EXEC_HOOK), og); + execute_shell_function (hookf, wl); + } exec_done: QUIT;

One can then define function command_exec_handle() { eval $1; } which will be executed instead of the original command given in the prompt. The original command is fully in the first parameter. The command_exec_handle can be given in .bashrc and it works as expected.

Notice: this is very dangerous! If you mess up and put a bad command_exec_handler in your .bashrc, you might end up with a shell that does not execute commands. It will be quite hard to fix without booting from a live cd.

vfalcao · Accepted Answer · 2019-03-19 15:34:12Z

It seems you have the same problem listed here. If you want to run some commands if your original command was not found, the Bash 4's command_not_found_handler will certainly fit your needs.

Try to be more specific, maybe with some code snippets that do or do not work, in order to help us to help you...

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