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Alerting long commands in zsh

Posted on 4 mins read

Update (2019-10-03): I fleshed this out into a plugin! Check it out https://github.com/kevinywlui/zlong_alert.zsh!

I often find myself running commands that take a long time and then coming back to it later. For example, when I’m running a long computation for my research or when I’m building a package. I recently discovered this zbell gist which seems to be almost exactly what I want! I’m trying to learn more shell scripting so I’m going to reimplement this and explain what I’m doing. The final version will be this

# Ignore commands if they start with the follow
zlong_ignore_cmds='vim ssh'

# Define what a long duration is
zlong_duration=60

# Need to set an initial timestamps otherwise, we'll be comparing an empty
# string with an integer.
zlong_timestamp=$EPOCHSECONDS

# Define the alerting function, do the text processing here
zlong_alert_func() {
    local cmd=$1
    local secs=$2
    local ftime=$(printf '%dh:%dm:%ds\n' $(($secs / 3600)) $(($secs % 3600 / 60)) $(($secs % 60)))
    notify-send "Done: $1" "Time: $ftime"
    echo "\a"
}

zlong_alert_pre() {
    zlong_timestamp=$EPOCHSECONDS
    zlong_last_cmd=$1
}

zlong_alert_post() {
    local duration=$(($EPOCHSECONDS - $zlong_timestamp))
    local lasted_long=$(($duration - $zlong_duration))
    local cmd_head=$(echo $zlong_last_cmd | cut -d ' ' -f 1)
    if [[ $lasted_long -gt 0 && ! -z $zlong_last_cmd && ! *"$cmd_head"*==zlong_ignore_cmds ]]; then
        zlong_alert_func $zlong_last_cmd duration
    fi
    zlong_last_cmd=''
}

add-zsh-hook preexec zlong_alert_pre
add-zsh-hook precmd zlong_alert_post

Overview

The goal of this script is to alert me whenever a command, that has taken over 60 seconds, is complete. I will be use notify-send to alert me and also send a bell character.

For my particular desktop setup, notify-send will alert me via dunst and the bell will set my kitty terminal to urgent which i3wm will pick up on and turn the workspace indicator red.

So my alert function will send me the command that was ran, the duration formatted nicely, and a bell character.

zlong_alert_func() {
    local cmd=$1
    local secs=$2
    local ftime=$(printf '%dh:%dm:%ds\n' $(($secs / 3600)) $(($secs % 3600 / 60)) $(($secs % 60)))
    notify-send "Done: $1" "Time: $ftime"
    echo "\a"
}

Timing commands

The zsh/datetime module gives us the EPOCHSECONDS parameter which is the number of seconds since the unix epoch. To determine the duration, we just need to subtract EPOCHSECONDS when the command is complete from EPOCHSECONDS when the command started. We will use zsh hooks for this.

Zsh hooks

One of the advantages of zsh over bash is that you get hooks. For this script, we’re interested in

  • preexec which “executed just after a command has been read and is about to be executed.”

  • precmd which “executed before each prompt.”

zlong_alert_pre() {
    zlong_timestamp=$EPOCHSECONDS
    zlong_last_cmd=$1
}

zlong_alert_post() {
    local duration=$(( $EPOCHSECONDS - $zlong_timestamp ))
    local lasted_long=$(( $duration - $zlong_duration ))
    if [[ $lasted_long -gt 0 ]]; then
        zlong_alert_func $zlong_last_cmd duration
    fi
}

add-zsh-hook preexec zlong_alert_pre
add-zsh-hook precmd zlong_alert_post

Ignore some commands

I use vim and ssh often and it doesn’t really make sense to count them as a long command. I store the commands I want to ignore in a comma separated list at the top, I can extract the head of a command as follows:

cmd_head=\$(echo $zlong_last_cmd | cut -d ' ' -f 1)
and substring testing is done using the star wildcard

*"$cmd_head"*==zlong_ignore_cmds

Fixing a zbell bug

In the zbell gist, there was a super annoying bug! If you run ls, wait long enough, then press ctrl-c, it’ll alert you! This is because preexec did not get a chance to run again but precmd did so it’ll count the duration as the time since the ls command. This was fix by setting zlong_last_cmd to be the empty string at the end of preexec then checking to see if the string is non-empty before sending it to the alert function.

Alternatives

One alternative to alerting the end of long commands that I should mention is using Pushbullet. Pushbullet is an app that I have installed on my phone that can send me notifications. The best part about Pushbullet is that it has an API. I’ve use https://github.com/Red5d/pushbullet-bash to send me an alert of my phone whenever a long computation I was doing for my research has finished.

Another cool zsh feature is REPORTTIME. This won’t alert you but it’ll tell you how long a command has run for. For example, by setting REPORTTIME=3, zsh will tell me the run duration of any command that takes more than 3 second.

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