Use "-s FILENAME" to return the size (in bytes) of a file, see perlfunc for more info. You'd want something like this

if (-s $fileOne != -s $fileTwo) {
    print "have different sizes\n";
} else {
    print "the same size\n";
};
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Some other things to think about:

• You are trying to read all of file2 every time find a match in file1. It's probably simpler to read file2 once and cache the results.
• Since you're not re-opening INfile2 that inner loop is probably not doing what you want...
• The regex you have will ignore the full path since it won't match the "/" character - this may or may not be what you want...

Hope this helps.