Renowned mathematician Stephen Kleene built a model in the year 1956 using finite automata for simple algebra. He described regular languages using his mathematical notation called regular sets. Computer programmers started using regular expressions in the 1970s when the Unix operating system and some of its text editors and text processing utilities such as ed, sed, emacs, lex, vi, grep, awk, and so on were built. Regular expressions gained more popularity with the arrival of Perl and Tcl scripting languages in the 1980s and 1990s. Since then, all the popular programming languages, such as Java, Python, Ruby, R, PHP, and .NET have built very good support of regular expressions.