If you meant how to treat a scalar like a file, then you want to use open with a reference to the scalar:

my $data = 'Hello World';
open my $fh, '>', \$data
    or die "Couldn't open \$data as a file";
seek $fh, 6;
print <$fh>
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But then again, your question is a bit vague, so I don't know if that's what you're looking for.