start process if not running, else ignore. Prevents cronjob overlap

lazycron.bash

#!/bin/bash
# portable way to ensure :              
#
#   * only one process at the time (prevents process-overlap, handy for cron workers)
#   * reverse cron's email behaviour (only emails on error)
#   * ultraportable: only reliest on flock, not on debians 'start-stop-daemon' or centos 'daemon'
#   * readable process names in top     
# 
# usage: ./lazycron <my-unique-id> <application> [args]
# example: ./lazycron cron-my-process php foo.php
#          ./lazycron cron-my-process bash /home/foo/myscript
#          ./lazycron cron-my-process bash /home/foo/myscript
# 
# there's is no output unless there are errors. This is handy in respect to cron's MAILTO variable:
# the stdout/stderr output will be suppressed (so cron will not send mails) *unless* the given process
# has an exitcode > 0                   
# 
# tests: https://gist.github.com/coderofsalvation/11254628
PROCESSNAME="$1"
BIN="$(which "$2")"
PROCESSBIN="/tmp/$(basename $2).$PROCESSNAME"
STARTDIR="$(dirname "$(readlink -f "$0")" )/../"
EXITCODE=0
STDOUT="/tmp/.lazycron.$PROCESSNAME"    
LOCKFILE="$STDOUT.lock"
NICELEVEL=10

[[ ! -f "$PROCESSBIN" ]] && cp "$BIN" "$PROCESSBIN"
shift; shift; # delete the first args   

trap "rm $LOCKFILE" 0 1 2 3 13 15 # cleanup upon EXIT HUP INT QUIT PIPE TERM

cd "$STARTDIR"; exec nice -n $NICELEVEL /usr/bin/flock -w 0 "$LOCKFILE" "$PROCESSBIN" "$@" > "$STDOUT"

# output stdout to cron *only* on error 
EXITCODE=$$; [[ ! $EXITCODE == 0 ]] && cat "$STDOUT"

exit $EXITCODE