Command durations in Powerline

Powerline is an easy way to make your shell prompt more informative (and fancy). One of the things it shows is the exit code (if non-zero) of the last command. It seems also useful to show the duration of the last command.

The fish shell conveniently provides an environment variable CMD_DURATION that stores the duration of the last command in milliseconds, and someone on GitHub showed how to display that in Powerline. I wanted to make this a little nicer by displaying the duration only if the command actually took, say, more than half a second to run, and also by converting the time to seconds.

The following fish function does just that:

function fish_postexec --on-event fish_postexec
    if test $CMD_DURATION -gt 500
        set --export --global CMD_DURATION_STR (math --scale=1 $CMD_DURATION / 1000)s
    else
        set --erase CMD_DURATION_STR
    end
    # avoid the duration being shown more than once
    # (this can happen when pressing Enter without entering a command)
    set CMD_DURATION 0
end

To use it, put this segment in your Powerline theme:

{
    "function": "powerline.segments.common.env.environment",
    "priority": 10,
    "args": {
        "variable": "CMD_DURATION_STR"
    }
}

The result