Regular Expressions

• Don't use regular expressions if you just need plain text search in string: string["text"] ^[link]

• For simple constructions you can use regexp directly through string index. ^[link]

  match = string[/regexp/]             # get content of matched regexp
  first_group = string[/text(grp)/, 1] # get content of captured group
  string[/text (grp)/, 1] = "replace"  # string => "text replace"
  

• Use non-capturing groups when you don't use the captured result. ^[link]

  # bad
  /(first|second)/
  
  # good
  /(?:first|second)/
  

• Avoid using numbered groups as it can be hard to track what they contain. Named groups can be used instead. ^[link]

  # bad
  /(regexp)/ =~ string
  ...
  process Regexp.last_match(1)
  
  # good
  /(?<meaningful_var>regexp)/ =~ string
  ...
  process meaningful_var
  

• Character classes have only a few special characters you should care about: ^, -, \, ], so don't escape . or brackets in []. ^[link]

• Be careful with ^ and $ as they match start/end of line, not string endings. If you want to match the whole string use: \A and \z (not to be confused with \Z which is the equivalent of /\n?\z/). ^[link]

  string = "some injection\nusername"
  string[/^username$/]   # matches
  string[/\Ausername\z/] # doesn't match
  

• Use x modifier for complex regexps. This makes them more readable and you can add some useful comments. Just be careful as spaces are ignored. ^[link]

  regexp = /
    start         # some text
    \s            # white space char
    (group)       # first group
    (?:alt1|alt2) # some alternation
    end
  /x
  

• For complex replacements sub/gsub can be used with a block or a hash. ^[link]

  words = "foo bar"
  words.sub(/f/, "f" => "F") # => "Foo bar"
  words.gsub(/\w+/) { |word| word.capitalize } # => "Foo Bar"