Regular Expressions in PHP, MySQL by programmerblog.net

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Regular Expressions in PHP

 Regular Expressions
 Regular expressions provide the foundation for describing or matching data according to
defined syntax rules. A regular expression is nothing more than a pattern of characters itself,
matched against a certain parcel of text.
 PHP offers functions specific to two sets of regular expression functions, each
corresponding
to a certain type of regular expression: POSIX and Perl-style.
 Regular Expression Syntax (POSIX)

 Quantifiers
 The frequency or position of bracketed character sequences and single characters can be denoted by a
special character, with each special character having a specific connotation. The +, *, ?, {occurrence_range}
 The frequency or position of bracketed character sequences and single characters can be denoted by a
special character, with each special character having a specific connotation. The +, *, ?,
{occurrence_range} , and $
 Brackets
 Brackets ([]) have a special meaning when used in the context of regular expressions, which are used to
find a range of characters.
 The regular expression [php] will find any string containing the character p or h
 [0-9] matches any decimal digit from 0 through 9.
 [a-z] matches any character from lowercase a through lowercase z.
 [A-Z] matches any character from uppercase A through uppercase Z.
 [A-Za-z] matches any character from uppercase A through lowercase z.
 p+ matches any string containing at least one p.
 p* matches any string containing zero or more p’s.
 p? matches any string containing zero or one p.
 p{2} matches any string containing a sequence of two p’s.
 p{2,3} matches any string containing a sequence of two or three p’s.

Regular Expressions
 p{2,} matches any string containing a sequence of at least two p’s.
 p$ matches any string with p at the end of it.
 Still other flags can precede and be inserted before and within a character sequence:
 ^p matches any string with p at the beginning of it.
 [^a-zA-Z] matches any string not containing any of the characters ranging from a
 through z and A through Z.
 p.p matches any string containing p, followed by any character, in turn followed by
 another p.
 ^.{2}$ matches any string containing exactly two characters.
 (.*) matches any string enclosed within and (presumably HTML bold tags).
 p(hp)* matches any string containing a p followed by zero or more instances of the sequence hp.
 Search for these special characters in strings
 The characters must be escaped with a backslash (). For example, if you wanted to search for a dollar
amount, a plausible regular expression would be as follows: ([$])([0-9]+); that is, a dollar sign followed by
one or more integers.
 $42, $560, and $3.
 Predefined Character Ranges (Character Classes)
 For your programming convenience, several predefined character ranges, also known as character
 classes, are available.
 [:alpha:]: Lowercase and uppercase alphabetical characters. This can also be specified as [A-Za-z].

Regular Expressions
 Regular Expression Will match...
 foo The string "foo"
 ^foo "foo" at the start of a string
 foo$ "foo" at the end of a string
 ^foo$ "foo" when it is alone on a string
 [abc] a, b, or c
 [a-z] Any lowercase letter
 [^A-Z] Any character that is not a uppercase letter
 (gif|jpg) Matches either "gif" or "jpeg"
 [a-z]+ One or more lowercase letters
 [0-9.-] Аny number, dot, or minus sign
 ^[a-zA-Z0-9_]{1,}$ Any word of at least one letter, number or _
 ([wx])([yz]) wy, wz, xy, or xz
 [^A-Za-z0-9] Any symbol (not a number or a letter)
 ([A-Z]{3}|[0-9]{4}) Matches three letters or four numbers

Regular Expressions
 Regular Expression Syntax (Perl Style)
 The developers of PHP felt that instead of reinventing the regular expression wheel, so to speak, they
should make the famed Perl regular expression syntax available to PHP users, thus the Perl-style functions.
 . Match any character
 ˆ Match the start of the string
 $ Match the end of the string
 s Match any whitespace character
 d Match any digit
 w Match any “word” character
 A: Matches only at the beginning of the string.
 b: Matches a word boundary.
 B: Matches anything but a word boundary.
 A caret (^) character at the beginning of a regular expression indicates that it must match the beginning of
the string.
 The dot (.) metacharacter matches any single character except newline (). So, the pattern h.t matches hat,
hothit, hut, h7t, etc.
 The vertical pipe (|) metacharacter is used for alternatives in a regular expression. It behaves much like a
logical OR operator

Regular Expressions
 The metacharacters +, *, ?, and {} affect the number of times a pattern should be matched.
 + means "Match one or more of the preceding expression", * means "Match zero or more of the preceding
expression",
 ? means "Match zero or one of the preceding expression".
 Curly braces {} can be used differently. With a single integer,
 {n} means "match exactly n occurrences of the preceding expression", with one integer and a comma, {n,}
means "match n or more occurrences of the preceding expression", and with two comma-separated integers
{n,m} means "match the previous character if it occurs at least n times, but no more than m times".
 /food/
 Notice that the string food is enclosed between two forward slashes. Just like with POSIX regular
expressions, you can build a more complex string through the use of quantifiers:
 /fo+/
 This will match fo followed by one or more characters. Some potential matches include
 food, fool, and fo4
 PHP’s Regular Expression Functions (Perl Compatible)
 preg_grep()
 array preg_grep (string pattern, array input [, flags])
 The preg_grep() function searches all elements of the array input, returning an array consisting of
 all elements matching pattern.

Regular Expressions
 $foods = array("pasta", "steak", "fish", "potatoes");
 $food = preg_grep("/^p/", $foods);
 print_r($food);
 preg_match()
 int preg_match (string pattern, string string [, array matches]
 [, int flags [, int offset]]])
 The preg_match() function searches string for pattern, returning TRUE if it exists and FALSE
 otherwise. The optional input parameter pattern_array can contain various sections of the
 subpatterns contained in the search pattern
 <?php
 $line = "Vim is the greatest word processor ever created!";
 if (preg_match("/bVimb/i", $line, $match)) print "Match found!";
 ?>
 preg_match_all()
 int preg_match_all (string pattern, string string, array pattern_array
 [, int order])
 The preg_match_all() function matches all occurrences of pattern in string, assigning each occurrence to
array pattern_array in the order you specify via the optional input parameter order.

Regular Expressions
 preg_replace_callback()
 mixed preg_replace_callback(mixed pattern, callback callback, mixed str
 [, int limit])
 Rather than handling the replacement procedure itself, the preg_replace_callback() function delegates the
string-replacement procedure to some other user-defined function.
 preg_split()
 array preg_split (string pattern, string string [, int limit [, int flags]])
 The preg_split() function operates like pattern can also be defined in terms of a regular expression.
 <?php
 $delimitedText = "+Jason+++Gilmore+++++++++++Columbus+++OH";
 $fields = preg_split("/+{1,}/", $delimitedText);
 foreach($fields as $field)
 echo $field." ";
 ?>
 OUTPUT:
 Jason
 Gilmore
 Columbus
 OH

Regular Expressions
 ereg($p,$str)
 ergi($p,$str)
 $ereg_replace($p,$r, $str)
 sql_regcase($p)
 split($p,$str)
 preg_match();
 pre_match_all()
 preg_replace()
 preg_split()

Regular Expressions in PHP, MySQL by programmerblog.net

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Regular Expressions in PHP, MySQL by programmerblog.net