However, the semantics differ considerably. Wildcards, also known as globbing, look very similar in their syntax to regular expressions. There is another mechanism in operating systems, which shouldn't be mistaken for regular expressions. The first programs which had incorporated the capability to use regular expressions were the Unix tools ed (editor), the stream editor sed and the filter grep. Python, Perl, Java, SED, AWK and even X#. A great thing about regular expressions: The syntax of regular expressions is the same for all programming and script languages, e.g. It's possible to check, if a text or a string matches a regular expression. Regular Expressions are used in programming languages to filter texts or textstrings. You can find an implementation of a Finite State Machine in Python on our website. A finite state machine (FSM), which accepts language defined by a regular expression, exists for every regular expression. In theoretical computer science, they are used to define a language family with certain characteristics, the so-called regular languages. The term "regular expression", sometimes also called regex or regexp, has originated in theoretical computer science. This introduction will explain the theoretical aspects of regular expressions and will show you how to use them in Python scripts. The aim of this chapter of our Python tutorial is to present a detailed and descriptive introduction into regular expressions.
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