How long do commands run?

• 2024-08-30
• bash,
• uv

One of the most remarkable things about uv is just how fast it is. In fact, Charlie Marsh and the Astral team have been such an inspiration, that I got curious about how long commands take.

So I did the natural thing and updated my ~/.bashrc (I'll update my .zshrc soon) to change my prompt to display the number of milliseconds the previous command took.

At the very top of the file, I define a variable to hold the current time in nanoseconds. Putting this here lets me know how long the .bashrc itself takes to run.

Then I used preexec() to record the start time of every command. To make this work properly, you need to download bash-preexec.

Finally, I used PROMPT_COMMAND which will get called to produce my prompt. To add a splash of color (i.e. red if the previous command failed), I used brush.

Putting it all together:

# very top of ~/.bashrc
_time_cmd=$(date +%s%N)

# <snip>

# https://github.com/metaist/brush
source ~/.local/bin/brush

preexec() { # record command start time
    _time_cmd=$(date +%s%N)
}


PROMPT_COMMAND=__prompt_command
__prompt_command() {
    local code="$?" # must be first line in this function
    PS1="\[\e]0;\w\a\]\n" # set terminal title

    # <snip>

    # add run time of previous command (in red if error)
    PS1+="$(brush reset)"
    if [[ "$code" != "0" ]]; then
        PS1+=$(brush bgRed)
    fi
    PS1+=$(( ( $(date +%s%N) - $_time_cmd ) / 1000000 ))ms
    PS1+="$(brush reset)"

    # <snip>

    PS1+="\n\$ "
}

# <snip>

# https://github.com/rcaloras/bash-preexec
source ~/.bash-preexec.sh # must be last import

# very bottom