Regular expressions are nothing more than a pattern or series of characters itself. They provide the foundation for pattern-matching functionality.
Using regular expression, you can search a specific string inside of another string, you can replace a string by another string and you can divide a string into many chunks.
PHP gives functions that are specific to two sets of Regular Expression functions, each corresponding to a specific type of regular expression. You can use any of them based on your requirement.
- POSIX Regular Expressions
- PERL Style ReExp
POSIX Regular Expressions
The simplest regular expression is the one that matches a single character, such as g, inside the strings, such as g, bottle, or bag.
Lets give explanation for few concepts that are being used in POSIX regular expression. After that we will introduce to you guys the regular expression related functions.
Brackets
Sr.No | Expression & Description |
---|---|
1 | [0-9] It matches any decimal digit from 0 through 9. |
2 | [a-z] It matches any character from lower-case a through lowercase z. |
3 | [A-Z] It matches any character from uppercase A through uppercase Z. |
4 | [a-Z] It matches any character from lowercase a through uppercase Z. |
Quantifiers
Sr.No | Expression & Description |
---|---|
1 | p+ It matches any string containing at least one p. |
2 | p* It matches any string containing zero or more p's. |
3 | p? It matches any string containing zero or one p's. |
4 | p{N} It matches any string containing a sequence of N p's |
5 | p{2,3} It matches any string containing a sequence of two or three p's. |
6 | p{2, } It matches any string containing a sequence of at least two p's. |
7 | p$ It matches any string with p at the end of it. |
8 | ^p It matches any string with p at the beginning of it. |
Example
Sr.No | Expression & Description |
---|---|
1 | [^a-zA-Z] It matches any string not containing any of the characters ranging from a through z and A through Z. |
2 | p.p It matches any string containing p, followed by any character, in turn followed by another p. |
3 | ^.{2}$ It matches any string containing exactly two characters. |
4 | <b>(.*)</b> It matches any string enclosed within <b> and </b>. |
5 | p(hp)* It matches any string containing a p followed by zero or more instances of the sequence php. |
Predefined Character Ranges
Sr.No | Expression & Description |
---|---|
1 | [[:alpha:]] It matches any string containing alphabetic characters aA through zZ. |
2 | [[:digit:]] It matches any string containing numerical digits 0 through 9. |
3 | [[:alnum:]] It matches any string containing alphanumeric characters aA through zZ and 0 through 9. |
4 | [[:space:]] It matches any string containing a space. |
PHP Regexp POSIX Functions
Sr.No | Function & Description |
---|---|
1 | ereg() The ereg() function searches a string specified by string for a string specified by pattern, returning true if the pattern is found, and false otherwise. |
2 | ereg_replace() The ereg_replace() function searches for string specified by pattern and replaces pattern with replacement if found. |
3 | eregi() The eregi() function searches throughout a string specified by pattern for a string specified by string. The search is not case sensitive. |
4 | eregi_replace() The eregi_replace() function operates exactly like ereg_replace(), except that the search for pattern in string is not case sensitive. |
5 | split() The split() function will divide a string into various elements, the boundaries of each element based on the occurrence of pattern in string. |
6 | spliti() The spliti() function operates exactly in the same manner as its sibling split(), except that it is not case sensitive. |
7 | sql_regcase() The sql_regcase() function can be thought of as a utility function, converting each character in the input parameter string into a bracketed expression containing two characters. |
PERL Style RegExp
Lets give explanation for few concepts that are used in PERL regular expressions. After that we are going to introduce you with the regular expression related functions.
Meta Characters
For example, you can look for large money sums making use of the '\d' meta character : /([\d]+)000/. So here \d will search for any string of numeric character.
The following is the list of meta characters that can be used in PERL Style Regexp.
Character Description
. a single character
\s a whitespace character (space, tab, newline)
\S non-whitespace character
\d a digit (0-9)
\D a non-digit
\w a word character (a-z, A-Z, 0-9, _)
\W a non-word character
[aeiou] matches a single character in the given set
[^aeiou] matches a single character outside the given set
(foo|bar|baz) matches any of the alternatives specified
Modifiers
Modifier Description
i Makes the match case insensitive
m Specifies that if the string has newline or carriage
return characters, the ^ and $ operators will now
match against a newline boundary, instead of a
string boundary
o Evaluates the expression only once
s Allows use of . to match a newline character
x Allows you to use white space in the expression for clarity
g Globally finds all matches
cg Allows a search to continue even after a global match fails
PHP Regexp PERL Functions
Sr.No | Function & Description |
---|---|
1 | preg_match() The preg_match() function searches string for pattern, returning true if pattern exists, and false otherwise. |
2 | preg_match_all() The preg_match_all() function matches all occurrences of pattern in string. |
3 | preg_replace() The preg_replace() function operates just like ereg_replace(), except that regular expressions can be used in the pattern and replacement input parameters. |
4 | preg_split() The preg_split() function operates exactly like split(), except that regular expressions are accepted as input parameters for pattern. |
5 | preg_grep() The preg_grep() function searches all elements of input_array, returning all elements matching the regexp pattern. |
6 | preg_ quote() Quote regular expression characters |
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