preg match - Regex: Specify "space or start of string" and "space or end of string"

Question

Imagine you are trying to pattern match "stackoverflow".

You want the following:

 this is stackoverflow and it rocks [MATCH]

 stackoverflow is the best [MATCH]

 i love stackoverflow [MATCH]

 typostackoverflow rules [NO MATCH]

 i love stackoverflowtypo [NO MATCH]

I know how to parse out stackoverflow if it has spaces on both sites using:

/s(stackoverflow)s/

Same with if its at the start or end of a string:

/^(stackoverflow)s/

/s(stackoverflow)$/

But how do you specify "space or end of string" and "space or start of string" using a regular expression?

Answer 1

You can use any of the following:

      #A word break and will work for both spaces and end of lines.
(^|s)  #the | means or. () is a capturing group. 


/(stackoverflow)/

Also, if you don't want to include the space in your match, you can use lookbehind/aheads.

(?<=s|^)         #to look behind the match
(stackoverflow)   #the string you want. () optional
(?=s|$)          #to look ahead.