int ereg ( string pattern, string string [, array regs])
Note: preg_match(), which uses a Perl-compatible regular expression syntax, is often a faster alternative to ereg(). Searches a string for matches to the regular expression given in pattern. If matches are found for parenthesized substrings of pattern and the function is called with the third argument regs, the matches will be stored in the elements of the array regs. $regs[1] will contain the substring which starts at the first left parenthesis; $regs[2] will contain the substring starting at the second, and so on. $regs[0] will contain a copy of the complete string matched. Note: Up to (and including) PHP 4.1.0 $regs will be filled with exactly ten elements, even though more or fewer than ten parenthesized substrings may actually have matched. This has no effect on ereg()'s ability to match more substrings. If no matches are found, $regs will not be altered by ereg(). Searching is case sensitive. Returns TRUE if a match for pattern was found in string, or FALSE if no matches were found or an error occurred.
Note: preg_match(), which uses a Perl-compatible regular expression syntax, is often a faster alternative to ereg(). Searches a string for matches to the regular expression given in pattern. If matches are found for parenthesized substrings of pattern and the function is called with the third argument regs, the matches will be stored in the elements of the array regs. $regs[1] will contain the substring which starts at the first left parenthesis; $regs[2] will contain the substring starting at the second, and so on. $regs[0] will contain a copy of the complete string matched. Note: Up to (and including) PHP 4.1.0 $regs will be filled with exactly ten elements, even though more or fewer than ten parenthesized substrings may actually have matched. This has no effect on ereg()'s ability to match more substrings. If no matches are found, $regs will not be altered by ereg(). Searching is case sensitive. Returns TRUE if a match for pattern was found in string, or FALSE if no matches were found or an error occurred.
具体你可以看php的手册,楼上的给你的就是手册里的东东,
当然你可以去找中文的手册的,而且很多的书中都有介绍.