It means that you can't modify $&. It's a read-only copy of the previous match.

You can use a substitution instead: 

$word =~ s/(whatever)U(whatever)/$1Ú$2/

[download]

Notice that you can't modify $$ either, which is the current process ID.

In reply to Re: $& as a read-only value by moritz
in thread $& as a read-only value by frasco

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