27. Metacharacters - Grouping Revisited

• Remember how we could use brackets to group, limiting the scope of alternation?

    gr(e|a)y
          

• Well, grouping also has some other neat uses.
• Firstly, we can use grouping to specify a set of multiple characters that we want to apply a quantifier to. For example, say that we want to search a list of phone numbers for numbers that have "8989" in them. Here's our list of numbers (example04.txt):

    8989 4325
    8998 0897
    8234 9889
    8715 8989
          

• We can run:

    egrep '(89){2}' example04.txt
          

  and we get:

    8989 4325
    8715 8989
          

• What? Why suddenly egrep? What's wrong with plain old grep?
• Sorry, but as we've seen before, not all regex tools are the same - grep doesn't support the use of plus and intervals on a group! We'll look at some tools and what they support later.