other programming environments as well. Induction Regular expressions can often be created ("induced" or "learned") based on a set of example strings. This is known as the induction of regular languages and is part of the general problem of grammar induction in computational learning theory. Formally, given examples of strings in a regular language, and perhaps also given examples of strings not in that regular language, it is possible to induce a grammar for the language, i.e., a regular expression that generates that language. Not all regular languages can be induced in this way (see language identification in the limit), but many can. For example, the set of examples {1, 10, 100}, and negative set (of counterexamples) {11, 1001, 101, 0} can be used to induce the regular expression 1⋅0* (1 followed by zero or more 0s). See also Comparison of regular-expression engines Extended Backus–Naur form Matching wildcards Regular tree grammar Thompson's construction – converts a regular expression into an equivalent nondeterministic finite automaton (NFA) Notes References External links ISO/IEC 9945-2:1993 Information technology – Portable Operating System Interface (POSIX) – Part 2: Shell and Utilities ISO/IEC 9945-2:2002 Information technology – Portable Operating System Interface (POSIX) – Part 2: System Interfaces ISO/IEC 9945-2:2003 Information technology – Portable Operating System Interface (POSIX) – Part 2: System Interfaces ISO/IEC/IEEE 9945:2009 Information technology – Portable Operating System Interface (POSIX) Base Specifications, Issue 7 Regular Expression, IEEE Std 1003.1-2017, Open Group 1951 introductions Articles with example code Automata (computation) Formal languages Pattern matching Programming constructs