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A metacharacter is a character that has a special meaning to a computer program, such as a shell interpreter or a regular expression (regex) engine.. In POSIX extended regular expressions, there are 14 metacharacters that must be escaped — preceded by a backslash (\) — in order to drop their special meaning and be treated literally inside an expression: opening and closing square brackets ...
An escape sequence starts with a backslash (\) called the escape character and subsequent characters define the meaning of the escape sequence. For example, \n denotes a newline character. The same or similar escape sequences are used in other, related languages such C++, C#, Java and PHP.
Perl Compatible Regular Expressions (PCRE) is a library written in C, which implements a regular expression engine, inspired by the capabilities of the Perl programming language. Philip Hazel started writing PCRE in summer 1997. [ 3 ]
Java Apache java.util.regex Java's User manual: Java GNU GPLv2 with Classpath exception jEdit: JRegex JRegex: Java BSD MATLAB: Regular Expressions: MATLAB Language: Proprietary Oniguruma: Kosako: C BSD Atom, Take Command Console, Tera Term, TextMate, Sublime Text, SubEthaEdit, EmEditor, jq, Ruby: Pattwo Stevesoft Java (compatible with Java 1.0 ...
Regular expressions are used in search engines, in search and replace dialogs of word processors and text editors, in text processing utilities such as sed and AWK, and in lexical analysis. Regular expressions are supported in many programming languages. Library implementations are often called an "engine", [4] [5] and many of these are ...
Bracket matching, also known as brace matching or parentheses matching, is a syntax highlighting feature of certain text editors and integrated development environments that highlights matching sets of brackets (square brackets, curly brackets, or parentheses) in languages such as Java, JavaScript, and C++ that use them. The purpose is to help ...
For certain regular expression operators like | (the operator for alternation or logical disjunction) it is superior to PCRE. Unlike PCRE, which supports features such as lookarounds, backreferences and recursion , RE2 is only able to recognize regular languages due to its construction using the Thompson DFA [ 4 ] algorithm.
Extreme examples occur when these are combined – Uniform Naming Convention paths begin with \\, and thus an escaped regular expression matching a UNC name begins with 8 backslashes, "\\\\\", due to needing to escape the string and the regular expression. Using raw strings reduces this to 4 (escaping in the regular expression), as in C# @"\\\\".