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A regular expression (shortened as regex or regexp), [1] sometimes referred to as rational expression, [2] [3] is a sequence of characters that specifies a match pattern in text. Usually such patterns are used by string-searching algorithms for "find" or "find and replace" operations on strings , or for input validation .
For example, an en dash is entered using ⌥ Opt+-; an em dash (—) is entered using ⇧ Shift+ ⌥ Opt+-. Also on a Macintosh pressing and holding certain letters (the vowels and a few other letters) brings up a pop-up menu of related special characters, such as accented versions of vowels, which can be clicked on or selected numerically.
Combining Diacritical Marks is a Unicode block containing the most common combining characters. It also contains the character " Combining Grapheme Joiner ", which prevents canonical reordering of combining characters, and despite the name, actually separates characters that would otherwise be considered a single grapheme in a given context.
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 ...
This is the "regular expression" (or regexp, or regex). Its metacharacters can represent multiple possibilities for a character position or a range of character positions within a page, using metacharacters for truth logic, grouping, counting, and modifying the characters to be found.
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 ...
Pd, dash Common ⸗ DOUBLE OBLIQUE HYPHEN U+2E17: Pd, dash Common ⸚ HYPHEN WITH DIAERESIS U+2E1A: Pd, dash Common ⸺ TWO-EM DASH U+2E3A: Pd, dash Common ⸻ THREE-EM DASH U+2E3B: Pd, dash Common ⹀ DOUBLE HYPHEN U+2E40: Pd, dash Common 〜 WAVE DASH U+301C: Pd, dash Common 〰 WAVY DASH U+3030: Pd, dash Common ゠ KATAKANA-HIRAGANA DOUBLE ...
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 ]