You cannot avoid using a different variable.

The usual idiom is:

    ($tmp = $string) =~ s/foo/blah/;
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If you want to combine it with calling a function, use Perls do:

    func do {(my $tmp = $string) =~ s/foo/blah; $tmp};
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Or

    func do {local $_ = $string; s/foo/blah; $_};
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-- Abigail