Regexps Regular expressions are used for complex string manipulation in PHP. The functions that support regular expressions are: ereg ereg_replace eregi eregi_replace split spliti These functions all take a regular expression string as their first argument. PHP uses the POSIX extended regular expressions as defined by POSIX 1003.2. For a full description of POSIX regular expressions see the regex man pages included in the regex directory in the PHP distribution. It's in manpage format, so you'll want to do something along the lines of man /usr/local/src/regex/regex.7 in order to read it. 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]. */ $string = ereg_replace ("^", "<BR>", $string); /* Put a <BR> tag at the beginning of $string. */ $string = ereg_replace ("$", "<BR>", $string); /* Put a <BR> tag at the end of $string. */ $string = ereg_replace ("\n", "", $string); /* Get rid of any newline characters in $string. */ ereg Regular expression match int ereg string pattern string string array regs 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 string. If ereg finds any matches at all, $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. The following code snippet takes a date in ISO format (YYYY-MM-DD) and prints it in DD.MM.YYYY format: if (ereg ("([0-9]{4})-([0-9]{1,2})-([0-9]{1,2})", $date, $regs)) { echo "$regs[3].$regs[2].$regs[1]"; } else { echo "Invalid date format: $date"; } See also eregi, ereg_replace, and eregi_replace. ereg_replace Replace regular expression string ereg_replace string pattern string replacement string string This function scans string for matches to pattern, then replaces the matched text with replacement. The modified string is returned. (Which may mean that the original string is returned if there are no matches to be replaced.) If pattern contains parenthesized substrings, replacement may contain substrings of the form \\digit, which will be replaced by the text matching the digit'th parenthesized substring; \\0 will produce the entire contents of string. Up to nine substrings may be used. Parentheses may be nested, in which case they are counted by the opening parenthesis. If no matches are found in string, then string will be returned unchanged. For example, the following code snippet prints "This was a test" three times: $string = "This is a test"; echo ereg_replace (" is", " was", $string); echo ereg_replace ("( )is", "\\1was", $string); echo ereg_replace ("(( )is)", "\\2was", $string); One thing to take note of is that if you use an integer value as the replacement parameter, you may not get the results you expect. This is because ereg_replace will interpret the number as the ordinal value of a character, and apply that. For instance: <?php /* This will not work as expected. */ $num = 4; $string = "This string has four words."; $string = ereg_replace('four', $num, $string); echo $string; /* Output: 'This string has words.' */ /* This will work. */ $num = '4'; $string = "This string has four words."; $string = ereg_replace('four', $num, $string); echo $string; /* Output: 'This string has 4 words.' */ ?> See also ereg, eregi, and eregi_replace. eregi case insensitive regular expression match int eregi string pattern string string array regs This function is identical to ereg except that this ignores case distinction when matching alphabetic characters. See also ereg, ereg_replace, and eregi_replace. eregi_replace replace regular expression case insensitive string eregi_replace string pattern string replacement string string This function is identical to ereg_replace except that this ignores case distinction when matching alphabetic characters. See also ereg, eregi, and ereg_replace. split split string into array by regular expression array split string pattern string string int limit Returns an array of strings, each of which is a substring of string formed by splitting it on boundaries formed by the regular expression pattern. If limit is set, the returned array will contain a maximum of limit elements with the last element containing the whole rest of string. If an error occurs, split returns false. To get the first five fields from a line from /etc/passwd: $passwd_list = split (":", $passwd_line, 5); To parse a date which may be delimited with slashes, dots, or hyphens: $date = "04/30/1973"; // Delimiters may be slash, dot, or hyphen list ($month, $day, $year) = split ('[/.-]', $date); echo "Month: $month; Day: $day; Year: $year<br>\n"; Note that pattern is case-sensitive. Note that if you don't require the power of regular expressions, it is faster to use explode, which doesn't incur the overhead of the regular expression engine. Please note that pattern is a regular expression. If you want to split on any of the characters which are considered special by regular expressions, you'll need to escape them first. If you think split (or any other regex function, for that matter) is doing something weird, please read the file regex.7, included in the regex/ subdirectory of the PHP distribution. It's in manpage format, so you'll want to do something along the lines of man /usr/local/src/regex/regex.7 in order to read it. See also: spliti, explode, and implode. spliti Split string into array by regular expression case insensitive array split string pattern string string int limit This function is identical to split except that this ignores case distinction when matching alphabetic characters. See also: split, explode, and implode. sql_regcase Make regular expression for case insensitive match string sql_regcase string string Returns a valid regular expression which will match string, ignoring case. This expression is string with each character converted to a bracket expression; this bracket expression contains that character's uppercase and lowercase form if applicable, otherwise it contains the original character twice. echo sql_regcase ("Foo bar"); prints [Ff][Oo][Oo][ ][Bb][Aa][Rr]. This can be used to achieve case insensitive pattern matching in products which support only case sensitive regular expressions.