Update: A regular expression would allow you to modify the text "in place" in your arrays. Others have suggested using split to break the text apart, which would work fine (and more efficiently) if you're wanting to just get at the text on either side of the equals sign. You could make your changes and re-combine the new left side and the old right side when you were done if you wanted. Otherwise...

I'm assuming that you mean that you have a list built sorta like this:

@listA = ('This=That', 'Some=Song');
@listB = ('Other=That', 'Corny=Song');
[download]

If you wish to change the text, you'd start off with this regular expression:

$text =~ s/.+?=/$new_text=/;
[download]

This will replace everything up to the equal sign with the text in $new_text. Now, to adapt it to modify the items in your arrays:

foreach (@listA, @listB) {   # or just one of the two, whatever
   # set $new_text to whatever you want
   s/.+?=/$new_text=/;
}
[download]

The trailing = sign after $new_text is necessary because my pattern (trying to keep it simple) also included an equal sign. You could just as easily do this:

s/.+?(?==)/$new_text/;
[download]

Hope this answers your question.