Perhaps this will work better for you (UNTESTED):

sub GROOMLDIF {
    # Delete LDAP-internal fields

    my $erasethese = qr/\A(?:structuralObjectClass|entryUUID|creatorsN
+ame|modifiersName|createTimestamp|modifyTimestamp|entryCSN):/;

    open my $IN,  '<', 'data/all.ldif'     or die "Cannot open 'data/a
+ll.ldif' $!";
    open my $OUT, '>', 'data/groomed.ldif' or die "Cannot open 'data/g
+roomed.ldif' $!";

    while ( <$IN> ) {
        print $OUT $_ unless /$erasethese/;
    }
}
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