How to use regular expressions in PHP

Regular expressions in PHP are used in the processing of complex strings. The supported regular expressions are as follows:

Ereg ()
Ereg_replace ()
Eregi ()
Eregi_replace ()
Split ()

(1) Ereg,eregi
This is a regular expression matching function, the former is case-insensitive, and the latter is irrelevant.
Usage:
Ereg (regular expression, string, [match part array name]);
Regular expressions in PHP3.0 are generally similar to those used in grep.

(2) Ereg_replace,eregi_replace
These are replacement functions.
Usage:
Ereg_replace (Regular expression, substitution string, original string);
A strtr in the string handler is a "translation" function, similar to the tr/.../.../in Perl,
Usage:
STRTR (String, "from", "to");
For example:
STRTR ("Aaabb", "AB", "CD") returns to "CCCDD".

(3) Split
It's similar to the explode function, but this time you can split the string at a place that matches a regular expression.
Usage:
Split (regular expression, string, [number of items taken out before]);


These functions use a regular string as the first argument. PHP uses the extended regular string defined by the POSIX 1003.2 standard. To examine the full description of POSIX regular expressions see the man page under the Regex directory in the PHP package.

Example 2-4. Regular expression Examples

Ereg ("abc", $string);
/* Returns true if "abc" is found anywhere in $string. */

Ereg ("^abc", $string);
/* Returns true if "abc" is found at the beginning of $string. */

Ereg ("abc$", $string);
/* Returns true if "abc" is found in the end of $string. */

Eregi ("(ozilla.[ 23]| MSIE.3) ", $HTTP _user_agent);
/* Returns True if client browser is Netscape 2, 3 or MSIE 3. */

Ereg ([: alnum:]]+) ([[: alnum:]]+) ([[: alnum:]]+), $string, $regs);
/* Places Three space separated words into $regs [1], $regs [2] and $regs [3]. */

Ereg_replace ("^", "
", $string);
* Put a
Tag at the beginning of $string. */

Ereg_replace ("$", "
", $string);
* Put a
Tag at the end of $string. */

Ereg_replace ("\ n", "", $string);
/* Get rid of any carriage return characters in $string. */