perl -alne 'print $F[1] if /user\@example.com/' /home/bob/db.txt

##</code><code>##

use warnings;
use strict;

open my $FH, '<', '/home/bob/db.txt' or die $!;

while (local $_ = <$FH>)
{
    chomp;
    print((split ' ')[1], "\n") if /user\@example.com/;
}