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).+(l.ng)/, 2] # gives long
Also often used: search and replace with
\1 gives the first found group,
\2 the second:
string.gsub(/(n.t).+(l.ng)/, '\1 very \2') # My not very long string
The last result is remembered and can be used on the following lines
$2 # gives long