Regular expression format_PHP tutorial

Regular expressions are used in PHP to process complex text strings. Functions that support regular expressions are:
ereg()
ereg replace()
eregi replace()
split()
These functions all take a regular expression as their first parameter. PHP uses POSIX extended regular expressions (using POSIX 1003.2). To find a complete description of POSIX extended regular expressions, check out the regex man page included with your PHP distribution.
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 at 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 ]. */