cron-unfuck

#!/usr/bin/env bash

# Usage: cron-unfuck PROG [ARG...]
#
# Just stick "cron-unfuck" in front of every line in your crontab, and
# watch problems go away. Basically, this script attempts to restore a
# somewhat more sane execution environment than cron natively
# provides, and then runs the provided command. Note that it exec's
# directly, so if you have a shell cmdline, provide the shell too.
#
# Things this does:
# * Eat all the output so that cron won't spam your MTA, and redirect
#   it to a logfile instead.
# * Add timestamps and metadata about command being executed to the
#   log.
# * Rotate the logfile if it gets too big.
# * Execute your ~/.profile so normal $PATH and envvars get setup.
# * Setup envvars for connecting to graphical environment, so stuff
#   like zenity will work out of the box.

if [[ -f /tmp/cron.log ]]; then
    logfile_mb="$(du -m /tmp/cron.log | awk '{print $1}')"
    if (( "${logfile_mb}" > 10 )); then
        tail < /tmp/cron.log -c5000000 > /tmp/cron.log.new
        mv /tmp/cron.log.new /tmp/cron.log
    fi
fi

{
    echo
    echo "[$(date)] cron-unfuck: invoking:" "$@"

    if uid="$(id -u)"; then
        export DBUS_SESSION_BUS_ADDRESS="unix:path=/run/user/${uid}/bus"
        export XDG_RUNTIME_DIR="/run/user/${uid}"
    fi

    if command -v systemd-run &>/dev/null; then
        env="$(systemd-run --user --pipe --collect -- env | (grep -E '^(DISPLAY|XAUTHORITY)=' ||:))"
        while IFS='=' read -r var val; do
            export "${var}=${val}"
        done <<< "${env}"
    else
        export DISPLAY=":0"
    fi

    # shellcheck disable=SC1091
    . "${HOME}/.profile"

    "$@" 2>&1

    echo "[$(date)] cron-unfuck: return code $?, finished invoking:" "$@"
} 2>&1 >>/tmp/cron.log