flex-old 2.5.4a-10ubuntu1 (amd64 binary) in ubuntu precise

 flex is a tool for generating scanners: programs which recognize lexical
 patterns in text. This is the old 2.5.4a version, which is no longer
 being developed. You should normally choose flex, unless you have
 legacy lexer files that do not work with a modern flex.
 .
 This product includes software developed by the University of California,
 Berkeley and its contributors. The upstream source code can be found at
 http://flex.sourceforge.net/