Hello guys,
this script partially works but it's still pretty ugly and, moreover, if the month is jan/feb/mar... it doesn't work at all.

Could anyone say me how to correct, cut and clean a little bit?

#!/usr/bin/ksh
[...]
egrep -v -e "^\s*#" /file/permission | awk '{ print $1 }' | sort | uniq | while read USER

do
LASTMONTH=`date "+%m"
let FIRSTMONTH=$LASTMONTH-3
let i=$FIRSTMONTH

 while [ $i -eq $LASTMONTH ]
  do
   n=`printf "%02d\n" $i`
   egrep $USER /var/log/access.2009$n >/dev/null || echo $USER >> $FILE
   let i=$i+1
  done
done

first thing i see is a missing ` at the end of the LASTMONTH line. next is the $LASTMONTH-3 should not work... should be something like "FIRSTMONTH=$(expr $LASTMONTH - 3)".
this isn't tested and so only a guess...

Not sure what you're trying to achieve, maybe you can do the whole stuff with one awk command.

for ` it was just a digit error.

I'm trying to verify if I could find a specific string ($USER) on last three months logs.
My logs files are like:

/var/log/access.200901
/var/log/access.200902
/var/log/access.200903
/var/log/access.200904