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The following subroutine returns its argument with any leading newline
+s
removed:

    sub xxx {
        my $s = shift;
        $s =~ s/^\n+//;
        $s;
    }

However, if this function is called from the replacement part of
a s///em, the /m semantics is carried over, and internal newlines
will be deleted.

I've confirmed the bug to be present in 5.000, 5.004_0[45], 5.005_0x,
5.6.x and 5.8.x, including 5.8.7. However, the bug isn't present in
any of the 5.9.x versions of perl.

Full test:

    #!/usr/bin/perl

    use strict;
    use warnings;
    no warnings qw /syntax/;

    use Test::More tests => 1;

    #
    # Delete any leading newlines.
    #
    sub xxx {
        my $s =  shift;
        $s =~ s/^\n+//;
        $s;
    }

    my $a = "A\n\nB"; $a =~ s/([\s\w]+)/xxx $1/e;
    my $b = "A\n\nB"; $b =~ s/([\s\w]+)/xxx $1/em;

    is ($b, $a);

    __END__

    1..1
    not ok 1
    #     Failed test (eep at line 21)
    #          got: 'A
    # B'
    #     expected: 'A
    #
    # B'
    # Looks like you failed 1 test of 1.
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Update::  

        (his previous SoPW is 'my' with 'if 0' retains old value, which probably wasn't on p5p as it has been beaten to death already),

Guess again ... Re: 'my' with 'if 0' retains old value, points to the p5p site from which jesuashok plagiarized it.