~/bin: until-same

Imagine you've started downloading a large file from a server which doesn't support resuming. It's taking ages and you want to go to bed, but you also don't want the computer to stay on unnecessarily after completion of the download. What do you do?

You use until-same: a simple shell command that repeats a command until it's output is the same twice in a row.

$ until-same -h
usage: until-same [ -v ] <interval> <command>

$ until-same 1m ls -l large.iso ; hibernate

<interval> uses the same syntax as the sleep command (not the shell builtin). -v simply prints the output of each command execution to stdout.

And here's the script:

#!/bin/sh

verbose=0
if [[ "$1" == "-v" ]]; then
    verbose=1
    shift
fi

if [[ "$1" == "-h" ]] || [[ -z "$1" ]] || [[ -z "$2" ]]; then
    echo "usage: until-same [ -v ] <interval> <command>"
    exit 1
fi

interval="$1"
shift
curr=`$@`
prev="$curr NOTTHESAME"

while [[ "$curr" != "$prev" ]]; do
    env sleep "$interval"
    prev="$curr"
    curr=`$@`
    [[ $verbose == 1 ]] && echo "$curr"
done