That is not a consequence of passing by reference, in fact. It is a consequence of aliasing. See perlsub for details. This would not happen if you use a different variable than @_: 
sub foo
{
    my $x = $_[0];
    print "$x\n";
    $x =~ /(.)/;
    print "$x\n\n";
}

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In reply to Re: Side effect of passing matched values by reference by choroba
in thread Side effect of passing matched values by reference by puterboy

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