[CentOS] if the file changes send email about diff

Sun Feb 6 13:33:35 UTC 2011
kellyremo <kellyremo at zoho.com>

I have 2 script. Script "A", Script "B".

Script "A" is regulary watching the "dhcpacks" [dhcp release is configured to 2mins] in the logs, for the past 2 minutes. it writes the MAC addresses to a file [/dev/shm/dhcpacks-in-last-2min.txt] every 2 minutes. Ok, this is working, active clients are in this file. Super!

Script "B": http://pastebin.com/raw.php?i=wvhwhPWu
I'm trying to create a script, that watches the changes in "/dev/shm/dhcpacks-in-last-2min.txt" file [in every 1 sec]. Ok. But: my "watcher" script [the pastebined] is not working fine...sometime it works, sometime it send that someone "XY logged out", but it's not true! nothing happened, and the problem is not in the Script "A".

Can someone help me point out, what am i missing? How can i watch a file [in every sec], that contains only MAC addresses, and if someone doesn't get dhcpack in 2 minutes, the file "/dev/shm/dhcpacks-in-last-2min.txt" changes, and that clients MAC address will be gone from it, and i need to know, who was it [pastebined my script..but somethings wrong with it].

Thank you for any help..i've been pathing my script for days now.. :\

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