Shell Programming and Scripting

Say I do a date command and get the time from 15 minutes ago.

I have a text file with the date printed out every minute or so and I want to cut the file at the date stamp given to me by the 15 minute ago time stamp.

Is there an easy way to do this?

Example:

date +%M gives me 56

I stick that in a variable.

Then I want to scroll through some text file and say "Oh, here is the first 56 in a line. Cut here and stick the remainder in some other file."

Seems so easy... just dont know the command.

Code:

#!/bin/ksh

INPUTFILE=$1
OUTPUTFILE=$2
TIMESTAMP=$(date +%M)

sed -n 's/.*\('${TIMESTAMP}'.*\)/\1/p' ${INPUTFILE} > ${OUTPUTFILE}

Similar problem, I have a log file with some lines contain timestamp but some don't. I want to search only the last 15 min log. Since not all lines have timestamp, the sed solution won't work cause will filter out some info that doesn't have timestamp. Any suggestion ?