Regular expressions in Ruby

regexp_ruby.md

Regexp and match groups in ruby

There is multiple ways to use regular expressions with ruby.

Simple example

We're going to use the following pattern: /\A\d{3}-[\w-]+\.\w{3,4}\z/

pattern = /\A\d{3}-[\w-]+\.\w{3,4}\z/
pattern =~ "215-hello-world.avi"     # => 0
pattern =~ "test.mp3"                # => 0

Match Groups

A usefull feature is to group each matched string. For this we're going to use parentheses:

pattern = /\A(\d{3})-([\w-]+)\.(\w{3,4})\z/
pattern =~ "215-hello-world.avi"     # => 0
$1                                   # => "215"
$2                                   # => "hello-name"
$3                                   # => "avi"

MatchData object

If we use the match method we can look up match groups on the resulting MatchData object

pattern = /\A(\d{3})-([\w-]+)\.(\w{3,4})\z/
match_groups = pattern.match("215-hello-world.avi")
# => #<MatchData "215-hello-world...

match_groups[2]
# => "hello-world"

match_groups.captures
# => ["215", "hello-world", "avi"]

Named match groups

And what if we need to name our match groups?

pattern = /\A(?<num>\d{3})-(?<name>[\w-]+)\.(?<ext>\w{3,4})\z/
filename = "215-hello-world.avi"
match_groups = pattern.match(filename)
# => <MatchData "215-hello-world.avi" num:"215" name:"hello-world" ext:"avi">

match_groups[:ext]                        
# => "avi"