A locking cron job?! In bash?! You're joking right??

Because its one of those things that people often times need to do, and because usually people are at a complete loss as to HOW to accomplish this feat, here's a very simple template which you can use to add locking to a cron job (or any script, really).

It's got a decent feature set for the code-size: A) custom lock file, B) lock expiration, C) decent log type output, D) easily used to wrap another script, or set of scripts inside

#!/bin/bash

###
### Simple bash script locking illustration
###
### By: Demitrious S. Kelly
###
### FWIW: YMMV: Use at your own risk
###

LOCKFILE=/var/lib/locks/this_job.lock
LOCKEXPIRE=600
NOW=$(date +%s)
CONT=1

if [ -f $LOCKFILE ]
 then
  echo -e $(date)"\tLock Found"
  CONT=0
  LOCKTIME=$(cat $LOCKFILE)
  let LOCKELAPSED=$NOW-$LOCKTIME
  if [ $LOCKELAPSED -gt $LOCKEXPIRE ]
   then
    CONT=1
    echo -e $(date)"\tLock Expired ($LOCKELAPSED), Contnuing"
   else
    echo -e $(date)"\tLock Not Yet Expired ($LOCKELAPSED), Aborting"
  fi
 else
  echo -e $(date)"\tLock Not Found"
fi

if [ $CONT -eq 0 ]
 then
  exit 1
fi

echo -e $(date)"\tCreating Lockfile"
echo $NOW > $LOCKFILE

###
### Job goes below here, inside the lockfile wrapper
###

        echo $(date +%s) > $LOCKFILE
 ## do stuff
 ## ...
        echo $(date +%s) > $LOCKFILE
 ## do stuff
 ## ...
        echo $(date +%s) > $LOCKFILE
 ## do stuff
 ## ...

###
### Job goes above here, inside the lockfile wrapper
###

echo -e $(date)"\tRemoving Lockfile\r\n\r\n"
rm $LOCKFILE