ruby, using regex to find something in between two strings

Using Ruby + regex, given:

starting-middle+31313131313@mysite.com

I want to obtain just: 31313131313

ie, what is betwe开发者_StackOverflow中文版en starting-middle+ and mysite.com

Here's what I have so far:

to = 'starting-middle+31313131313@mysite.com'

to.split(/\+/@mysite.com.*/).first.strip

Between 1st + and 1st @:

to[/\+(.*?)@/,1]

Between 1st + and last @:

to[/\+(.*)@/,1]

Between last + and last @:

to[/.*\+(.*)@/,1]

Between last + and 1st @:

to[/.*\+(.*?)@/,1]

Here is a solution without regex (much easier for me to read):

i = to.index("+")
j = to.index("@")
to[i+1..j-1]

If you care about readability, i suggest to just use "split", like so: string.split("from").last.split("to").first or, in your case:

to.split("+").last.split("@").first

use the limit 2 if there are more occurancies of '+' or '@' to only care about the first occurancy: to.split("+",2).last.split("@",2).first

Here is a solution based on regex lookbehind and lookahead.

email = "starting-middle+31313131313@mysite.com"
regex = /(?<=\+).*(?=@)/
regex.match(email)
=> #<MatchData "31313131313">

Explanation

1. Lookahead is indispensable if you want to match something followed by something else. In your case, it's a position followed by @, which express as (?=@)

2. Lookbehind has the same effect, but works backwards. It tells the regex engine to temporarily step backwards in the string, to check if the text inside the lookbehind can be matched there. In your case, it's a position after +, which express as (?<=\+)

so we can combine those two conditions together.

lookbehind   (what you want)   lookahead
    ↓              ↓             ↓
 (?<=\+)           .*          (?=@)

Reference

Regex: Lookahead and Lookbehind Zero-Length Assertions