Hi, something you could try:

• Use of undefinded/empty/mistyped variable? → add use strict; use warnings; at the begin of your program and run again
• Reading from STDIN? → enter Ctrl-D (Ctrl-Z on Windows) and see if the script continues
• What is read? → add a print "Reading: ($DIR_INPUT/$FILE)\n"; before the cat call
• Whitespace or special shell-characters in filename? → use `cat "$DIR_INPUT/$FILE" `
• Reading from FIFO? → check if the file your reading from is a regular one (e.g. warn("not a plain file - $FILE!") unless -f "$DIR_INPUT/$FILE");)

Seeing something unusual?

Update: Do it all with Perl - forget the cat and slurp the file; see How can I read in an entire file all at once?
Update2: If your environment/requirements allows that: Forget the slurp and read the page directly into $fileContent using e.g. LWP::Simple...