There are a number of different ways of doing this. The biggest problem to overcome is that normally, you can not have a file open for both reading and writing. You have to read the file in, make modifications, write to a new file, and then copy back over the original. There is a better way!!! I would recommend you use Tie::File (or learn $^I) Go to Tie::File

for (@array) {
 s/PERL/Perl/g;# Replace PERL with Perl everywhere in the file
}
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Changes you make to the array are reflected in the file immediately!