Suggested starting point

• Read the file into an array
• if $log_file[7]=~ /matches this/
• then $date = $log_file[0]
• else splice(@files,0,8) (Updated on the wise advice of moritz below)

Code that up, and see if it works, if not we can have a look, however without code or sample data we can only really have a punt @ this, the line to match may have unique characteristics, the other records may be different lengths, etc..