‘Gotcha’s 

• Or in Perl 5.14 ...

my @month = qw(Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec);

my @ymd = qw( 2001-08-31 1987-02-05 2003-03-12 1993-11-18 );

my @dmy = map {
    s/(\d\d\d\d)-(\d\d)-(\d\d)/$3 $month[$2 - 1] $1/r;
} @ymd;

say "$ymd[$_] => $dmy[$_]" foreach 0 .. 3;

2001-08-31 => 31 Aug 2001
1987-02-05 => 05 Feb 1987
2003-03-12 => 12 Mar 2003
1993-11-18 => 18 Nov 1993