Ruby Language Regular Expressions and Regex Based Operations Common quick usage


Regular expressions are often used in methods as parameters to check if other strings are present or to search and/or replace strings.

You'll often see the following:

string = "My not so long string"
string[/so/] # gives so
string[/present/] # gives nil
string[/present/].nil? # gives true

So you can simply use this as a check if a string contains a substring

puts "found" if string[/so/]

More advanced but still short and quick: search for a specific group by using the second parameter, 2 is the second in this example because numbering starts at 1 and not 0, a group is what is enclosed in parentheses.

string[/(n.t).+(, 2] # gives long

Also often used: search and replace with sub or gsub, \1 gives the first found group, \2 the second:

string.gsub(/(n.t).+(, '\1 very \2') # My not very long string

The last result is remembered and can be used on the following lines

$2 # gives long