| Regular Expression |
Article Index for Regular |
Website Links For Regular |
Information AboutRegular Expression |
| CATEGORIES ABOUT REGULAR EXPRESSION | |
| formal languages | |
| pattern matching | |
| programming language topics | |
|
Regular expressions are used by many Text Editor s, utilities, and programming languages to search and manipulate text based on patterns. For example, Perl and Tcl have a powerful regular expression engine built directly into their syntax. Several utilities provided by Unix distributions—including the editor Ed and the filter Grep —were the first to popularize the concept of regular expressions. "Regular expression" is often shortened to regex or '''regexp''' (singular), or '''regexes''', '''regexps''', or '''regexen''' (plural). As an example of the syntax, the regular expression \bex can be used to search for all instances of the string "''ex''" that occur at word boundaries (signified by the \b). Thus in the string, "Texts for experts," \bex matches the "''ex''" in "experts," but not in "Texts" (because the "''ex''" occurs inside the word there and not immediately after a word boundary).Many modern computing systems provide Wildcard Character s in matching filenames from a File System . This is a core capability of many Command-line Shells and is also known as Globbing . Wildcards differ from regular expressions in that they generally only express very restrictive forms of alternation. BASIC CONCEPTS | ||
| (''concatenation'') ''RS'' Denoting The Set { αβ α In ''R'' And β In ''S'' } For Example {"ab", "c"}{"d", "ef"} | {"abd", "abef", "cd", "cef"} |
|
| The Formal Definition Of Regular Expressions Is Purposely Parsimonious And Avoids Defining The Redundant Quantifiers <code></code> And <code>+</code>, Which Can Be Expressed As Follows: <code>a+</code> | <code>aa</code>, and <code>a</code> = <code>(aε)</code> Sometimes the complement operator ~ is added ~''R'' denotes the set of all strings over Σ that are not in ''R'' The complement operator is redundant, as it can always be expressed by using the other operators (although the process for computing such a representation is complex, and the result may be exponentially larger) |
|
| Since The Characters <code>(</code>, <code>)</code>, <code> | "</code>," class="copylinks" target="_blank"><code> </code>, <code></code>, <code></code>, <code></code>, <code>+</code>, <code>^</code>, <code></code>, and <code>$</code> are used as special symbols, they have to be Escaped if they are meant literally This is done by preceding them with <code>\</code>, which therefore also has to be escaped this way if meant literally |
|
| { Class | "wikitable" |
|
|