usr/sbin/runonce

#!/bin/bash

# Expansions of unset variables cause an error
set -u

# Given a script and it's content SHA-1, determine if it should run based upon
# whether its content has changed.
#
# Returns 0 if the script should run, other values indicate it should not run.
#
function should-run-script {
    local script="$1"; shift
    local script_sha1="$1"; shift
    local script_basename=$(basename "${script}")
    
    if [[ -f /var/cache/runonce/$script_basename ]]; then
        previous_sha1=$(cat /var/cache/runonce/$script_basename)

        if [[ $script_sha1 == $previous_sha1 ]]; then
            return 1
        fi
    fi

    return 0
}

function main {
    local script=""

    for script in /etc/runonce.d/*; do
        local script_sha1=$(sha1sum $script |awk '{ print $1 }')

        if ! should-run-script $script $script_sha1; then
            continue;
        fi

        $script

        if [[ $? == 0 ]]; then
            local script_basename=$(basename $script)
            echo $script_sha1 > /var/cache/runonce/$script_basename
            sync /var/cache/runonce/$script_basename
        fi
    done
}

main