1. You open the file and you close it, never read nor write from it. You should try and read up on file handles and loops.

Something ala..

while(my $line = <INHANDLE>)
{
   $line=~s/word1/word2/;
   print OUTHANDLE $line;
}
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2. If you are processing one file and wishing to change it, i might advise opening one file to read from as your original, and a tempfile as your output. modifying the file you are reading from works /sometimes/. Anyway, read your file in, and write out your changes to a temp file created via File::Temp.

When you are done closing your original and temp files, remove the original and rename the new to the old one.