Get last executed command in 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
}