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Diffstat (limited to 'pcre.html.markdown')
| -rw-r--r-- | pcre.html.markdown | 25 |
1 files changed, 17 insertions, 8 deletions
diff --git a/pcre.html.markdown b/pcre.html.markdown index 3e877a35..9e091721 100644 --- a/pcre.html.markdown +++ b/pcre.html.markdown @@ -3,16 +3,18 @@ language: PCRE filename: pcre.txt contributors: - ["Sachin Divekar", "http://github.com/ssd532"] - + --- -A regular expression (regex or regexp for short) is a special text string for describing a search pattern. e.g. to extract domain name from a string we can say `/^[a-z]+:/` and it will match `http:` from `http://github.com/`. +A regular expression (regex or regexp for short) is a special text string for describing a search pattern. e.g. to extract domain name from a string we can say `/^[a-z]+:/` and it will match `http:` from `http://github.com/`. PCRE (Perl Compatible Regular Expressions) is a C library implementing regex. It was written in 1997 when Perl was the de-facto choice for complex text processing tasks. The syntax for patterns used in PCRE closely resembles Perl. PCRE syntax is being used in many big projects including PHP, Apache, R to name a few. There are two different sets of metacharacters: + * Those that are recognized anywhere in the pattern except within square brackets + ``` \ general escape character with several uses ^ assert start of string (or line, in multiline mode) @@ -32,18 +34,19 @@ There are two different sets of metacharacters: ``` * Those that are recognized within square brackets. Outside square brackets. They are also called as character classes. - + ``` - + \ general escape character ^ negate the class, but only if the first character - indicates character range [ POSIX character class (only if followed by POSIX syntax) ] terminates the character class - -``` -PCRE provides some generic character types, also called as character classes. +``` + +PCRE provides some generic character types, also called as character classes. + ``` \d any decimal digit \D any character that is not a decimal digit @@ -59,7 +62,13 @@ PCRE provides some generic character types, also called as character classes. ## Examples -We will test our examples on following string `66.249.64.13 - - [18/Sep/2004:11:07:48 +1000] "GET /robots.txt HTTP/1.0" 200 468 "-" "Googlebot/2.1"`. It is a standard Apache access log. +We will test our examples on the following string: + +``` +66.249.64.13 - - [18/Sep/2004:11:07:48 +1000] "GET /robots.txt HTTP/1.0" 200 468 "-" "Googlebot/2.1" +``` + + It is a standard Apache access log. | Regex | Result | Comment | | :---- | :-------------- | :------ | |