expressionengine - Conditional using site_url is always false -

i trying use following conditional statement in template:

{if "{site_url}" == "http://dev.site.com" }     true {if:else}     false {/if} 

when test outputting site_url in template http://dev.site.com, expression evaluates false.

i've tried variations without brackets , quotes no luck.

try adding custom variable config.php (/system/expressionengine/config/ folder):

//###   custom variables   ### global $assign_to_config; $protocol = (isset($_server["https"]) && $_server["https"] == "on") ? "https://" : "http://"; $assign_to_config['global_vars'] = array(     "root_url"      => $protocol.$_server['http_host'],     "domain"        => $_server['http_host'] ); 

then change template be:

{if "{root_url}" == "http://dev.site.com" }     true {if:else}     false {/if} 

or

{if "{domain}" == "dev.site.com" }