用逗号分隔字符串

i have string

$string=" Tag tag1 tag2";

i want to output string with comma in form of:

OUTPUT:

Tag,tag1,tag2

$string=" Tag tag1 tag2";

print implode(',',explode(' ',trim($string)));
//or 
print str_replace(' ',',',trim($string));
//or 
print preg_replace('#( )#',',',trim($string));

http://php.net/manual/en/ref.strings.php