‘Gotcha’s 

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/;
} @ymd;

say $_ foreach @dmy;

1
1
1
1