Poor man's schema comparison Given two database definitions, it displays the difference in their schemas

schema_comparison

#!/usr/bin/perl
use strict;
use warnings;
use DBI;

my @dsn;
$dsn[0] = shift or help('no dns1');
$dsn[1] = shift or help('no dns1');

my @dbh;
my @schemas;

for my $i (0 .. 1) {
    my ($username, $password, $host, $port, $db) ;
    if ($dsn[$i] =~ m[
                mysql://
                (\S+)  # username
                :
                (\S+)  # password
                \@
                (\S+)  # hostname
                :
                (\d+)  # port number
                /
                (\w+)  # database
            ]x ) {
        ($username, $password, $host, $port, $db) = ($1, $2, $3 , $4, $5);
    }
    else {
        die "malformed identifier ($dsn[$i])\n";
    }
    my $dh = DBI->connect(sprintf( 'DBI:mysql:%s;host=%s;port=%s',
                $db, $host, $port),
      $username, $password, {RaiseError => 1})
	or die q{can't connect\n};
    print "ok $dsn[$i]\n";
    $dbh[$i] = $dh;
    $schemas[$i] = "$host:$port/$db";
}

for my $i ( 0 .. 1 ) {
    open my $FH, '>', "/tmp/tmp_schema$i.sql"
        or die "can't create schema$i.sql\n";
    print $FH "#\n# schema: ", $schemas[$i], "\n#\n\n";
    my $tables = $dbh[$i]->selectcol_arrayref(qq{SHOW TABLES});
    unless (@$tables) {
        die "no tables in dbh # $i\n";
    }
    for my $table (@$tables) {
        my $result = $dbh[$i]->selectall_arrayref(
                qq{SHOW CREATE TABLE `$table`});
        unless ($result) {
            die "can't get DDL for $table\n";
        }
        #use Data::Dumper;
        #print Dumper($result,"\n"); exit;
        my $create =  $result->[0][1];
        next unless $create =~ /^CREATE\s+TABLE/;
        print $FH "#\n# $table\n#\n\n";
        print $FH "$create;\n";
    }
    close $FH;
}

exec "vimdiff -o /tmp/tmp_schema0.sql /tmp/tmp_schema1.sql";

sub help {
    my ($msg) = @_;
    if ($msg) {
        print "*** $msg\n";
    }
    print "syntax: get_schema source target\n",
          "where source and target are \n",
          "mysql://username:password\@hostname:port/database\n";
    exit(1);
}

At lines 7 and 8:

$dsn[0] = shift or help('no dns1');
$dsn[1] = shift or help('no dns1');

The help message has a typo: "dns1"