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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 ...
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 ...
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 ]
The character sequence of two slash characters (//) after the string file: denotes that either a hostname or the literal term localhost follows, [3] although this part may be omitted entirely, or may contain an empty hostname. [4] The single slash between host and path denotes the start of the local-path part of the URI and must be present. [5]
Similarly, the vertical bar may see use as a delimiter for regular expression operations (e.g. in sed). This is useful when the regular expression contains instances of the more common forward slash (/) delimiter; using a vertical bar eliminates the need to escape all instances of the forward slash. However, this makes the bar unusable as the ...
The pgrep utility, for instance, displays the processes whose names match a given regular expression. [15] In the Perl programming language, grep is a built-in function that finds elements in a list that satisfy a certain property. [16] This higher-order function is typically named filter or where in other languages.
A slash placed through another operator is the same as placed in front. The prime symbol is placed after the negated thing, e.g. p ′ {\displaystyle p'} [ 2 ] ¬ ( ¬ A ) ⇔ A {\displaystyle \neg (\neg A)\Leftrightarrow A}
Also, a major portion of the utility commands packaged with MS-DOS 1.0 came from IBM and their command line syntax used the slash character as a 'switch' prefix. For example, dir /w runs the dir command with the wide list format option. This use of slash can still be found in the command interface under Microsoft Windows.