How I learned to stop worrying and love bash. ¶

I never really missed fancy syntax highlighting, or the nice globbing features, or most of ZSH really. The one thing I missed immensely was not so much a feature of ZSH as it was a feature of the Pure prompt I had been using: execution time for long-running commands shown in the prompt.

The time(1) command is a command that I never think to run until it’s too late. The Pure prompt is fancy. By default, if a particular command takes longer than 5 seconds to run, Pure calculates the running time of that command, and renders a human-readable version just above your current prompt.

~
❯ sleep 5

~ 5s
❯ sleep 10

~ 10s
❯

Bash it until it works ¶

Command execution time in Pure uses the preexec and precmd feature of ZSH, which doesn’t exist in Bash. Instead Bash has the less intuitive trap command and the PROMPT_COMMAND shell variable.

PROMPT_COMMAND is a variable that can be set in your bash config file that, “is executed as a command prior to issuing each primary prompt.” [bash(1)]

trap [-lp] [arg] [sigspec] can be used to listen for the DEBUG signal. “If a sigspec is DEBUG, the command arg is executed before every simple command”

Using these two tools in conjunction, you can approximate preexec and precmd:

debug() {
    # do nothing if completing
    [ -n "$COMP_LINE" ] && return

    # don't cause a preexec for $PROMPT_COMMAND
    [ "$BASH_COMMAND" = "$PROMPT_COMMAND" ] && return

    echo 'debug'
}

prompt() {
    echo 'prompt'
}

trap 'debug' DEBUG
PROMPT_COMMAND=prompt

So now debug is executed before each “simple command” and prompt is executed before each issuing the primary prompt.

$ echo 'hi'
debug
hi
prompt

Timing each command is then pretty trivial:

debug() {
    # do nothing if completing
    [ -n "$COMP_LINE" ] && return

    # don't cause a preexec for $PROMPT_COMMAND
    [ "$BASH_COMMAND" = "$PROMPT_COMMAND" ] && return

    start_time=$(date +'%s')
}

prompt() {
    end_time=$(date +'%s')

    echo "$(( end_time - start_time )) seconds"
}

trap 'debug' DEBUG
PROMPT_COMMAND=prompt

$ sleep 2
2 seconds
$

Integrating that into the prompt and making it look pretty is just a little-bit of code away:

# Human readable time output
# e.g., 5d 6h 3m 2s
format_time() {
  local _time=$1

  # Don't show anything if time is less than 5 seconds
  (( $_time < 5 )) && return

  local _out
  local days=$(( $_time / 60 / 60 / 24 ))
  local hours=$(( $_time / 60 / 60 % 24 ))
  local minutes=$(( $_time / 60 % 60 ))
  local seconds=$(( $_time % 60 ))
  (( $days > 0 )) && _out="${days}d"
  (( $hours > 0 )) && _out="$_out ${hours}h"
  (( $minutes > 0 )) && _out="$_out ${minutes}m"
  _out="$_out ${seconds}s"
  printf "$_out"
}

debug() {
    # do nothing if completing
    [ -n "$COMP_LINE" ] && return

    # don't cause a preexec for $PROMPT_COMMAND
    [ "$BASH_COMMAND" = "$PROMPT_COMMAND" ] && return

    start_time=$(date +'%s')
}

prompt() {
    end_time=$(date +'%s')
    time_f=$(format_time $(( end_time - start_time )))

    PS1="${time_f} (•◡•)❥"
}

trap 'debug' DEBUG
PROMPT_COMMAND=prompt

 (•◡•)❥ sleep 5
5s (•◡•)❥

Motherfucking magic.