Get last executed command in bash - bash

Question

I need to know what was the last command executed while setting my bash prompt in the function corresponding to PROMPT_COMMAND. I have code as follows
function bash_prompt_command () {
...
local last_cmd="$(history | tail -n 2 | head -n 1 | tr -s ' ' | cut -d ' ' -f3-)"
[[ ${last_cmd} =~ .*git\s+checkout.* ]] && ( ... )
...
}
Is there is faster(bash built-in way) to know the what was the command which invoked PROMPT_COMMAND.
I tried using BASH_COMMAND, but that too does not return the command which actually invoked PROMPT_COMMAND.

Answer 1

General case: Collecting all commands
You can use a DEBUG trap to store each command before it's run.
store_command() {
declare -g last_command current_command
last_command=$current_command
current_command=$BASH_COMMAND
return 0
}
trap store_command DEBUG
...and thereafter you can check "$last_command"
Special case: Only trying to shadow one (sub)command
If you only want to change how one command operates, you can just shadow that one command. For git checkout:
git() {
# if $1 is not checkout, just run real git and pretend we weren't here
[[ $1 = checkout ]] || { command git "$#"; return; }
# if $1 _is_ checkout, run real git and do our own thing
local rc=0
command git "$#" || rc=$?
ran_checkout=1 # ...put the extra code you want to run here...
return "$rc"
}
...potentially used from something like:
bash_prompt_command() {
if (( ran_checkout )); then
ran_checkout=0
: "do special thing here"
else
: "do other thing here"
fi
}