The file you are opening for read/write (+<) appears to be a text file with variable length records. You can't easily replace text records in place unless they are fixed length. There is really no such thing as a text file with records, it is just a string of characters, some of which happen to be new-line characters (that applies to UNIX and Windows anyway, some older systems did have real records).
I suggest you change your approach and write out a new file, then rename it on completion.
Please, don't use $a and $b, they are special variables in Perl and cause confusion.
Remember to place ^ and $ around your RE when describing a whole line.
Update: I misunderstood, and realise you are replacing strings of the same length. Your seek should probably be:
seek(FILE2, -(length $a), 1); (and you should chomp $file). But it is still messy.
Q. Are your data files realy double-spaced (\n\n between each record) or is that an aberation of cut-and-paste?

In reply to Re: how to match the pattern by using regexp for the below task by cdarke
in thread how to match the pattern by using regexp for the below task by Anonymous Monk

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