WHERE login_name=$user_login_name");

That's your problem. It should be

my $user_login_name = 'name.surname@company.com';

my $sth = $dbh->prepare("SELECT userid, login_name, realname FROM prof
+iles WHERE login_name = ? "); 

$sth->execute($user_login_name);
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Please read up on placeholders in the DBI manual.