正则表达式负前缀和后缀

Question

I have these strings for example:

download-google-chrome-free
download-mozilla-firefox-free

And also these strings:

google-chrome
mozilla-firefox

My prefix is ​​download- and my suffix is ​​-free , I need a regular expression to capture the words google-chrome , If the input string does not have download- and -free prefix and suffix, the group captured is the string itself.

String 1 = download-google-chrome-free (with prefix and sufix)

String 1 Group 1 = download-
String 1 Group 2 = google-chrome
String 1 Group 3 = -free

String 2 = google-chrome (without prefix and sufix)

String 2 Group 1 = '' (empty)
String 2 Group 2 = google-chrome (empty)
String 2 Group 3 = '' (empty)

You can do that? I am using PHP using preg_match .

Answer 1

preg_match('/(download-)?(google-chrome|mozilla-firefox)(-free)?/', $string, $match);

The ? indicates that the group before it is optional. If the prefix or suffix isn't in the string, those capture groups will be empty in $match .

If you don't actually want to return the groups with the optional prefix and suffix, make them non-capturing groups by putting ?: at the beginning of the group:

preg_match('/(?:download-)?(google-chrome|mozilla-firefox)(?:-free)?/', $string, $match);

Now $match[1] will contain the browser name that you want.