sub(...) public

Returns a copy of str with the first occurrence of pattern replaced with either replacement or the value of the block. The pattern will typically be a Regexp; if it is a String then no regular expression metacharacters will be interpreted (that is /\d/ will match a digit, but '\d' will match a backslash followed by a ‘d’).

If the method call specifies replacement, special variables such as $& will not be useful, as substitution into the string occurs before the pattern match starts. However, the sequences \1, \2, etc., may be used.

In the block form, the current match string is passed in as a parameter, and variables such as $1, $2, $`, $&, and $' will be set appropriately. The value returned by the block will be substituted for the match on each call.

The result inherits any tainting in the original string or any supplied replacement string.

   "hello".sub(/[aeiou]/, '*')               #=> "h*llo"
   "hello".sub(/([aeiou])/, '<\1>')          #=> "h<e>llo"
   "hello".sub(/./) {|s| s[0].to_s + ' ' }   #=> "104 ello"
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February 10, 2009
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Cheat Sheet

I have written a short introduction and a colorful cheat sheet for Perl Compatible Regular Expressions (PCRE) as used by Ruby’s Regexp class: