Posted by Matthew Weier O'Phinney on 10/21/91 11:15

* Jan <jjj@xs4all.nl>:
> Could someone explain to me the use of the vertical bar in
> expressions like "|<[^>]+>(.*)</[^>]+>|U". I understand that the
> vertical bars are used to separate the expression from the modifier,
> but can't find any documentation about the reasons and rules to do
> this.

This works in the PCRE functions, and has to do with the P in PCRE --
Perl. In perl, when performing a regexp, you can use whatever character
you desire to act as 'quotes' surrounding it. The typical one is a
forward slash, but when you are going to be matching forward slashes,
this can be inconvenient (the following examples are all perl, with a
PHP version follwing):

if ( /http:\/\/www.php.net\// ) # perl
if (preg_match('/http:\/\/www.php.net\//', $url)) # PHP

You get what's called 'leaning toothpick' syndrome. So, to make things
easier, you can specifiy a different regex delimiter:

if ( m|http://www.php.net| ) # perl
if (preg_match('|http://www.php.net|', $url) # PHP

(In perl, the 'm' indicates you're doing a match operation, and needs to
be present if you're using a delimiter other than a slash; it's not
necessary in PHP as it's implied.)

The modifier occurs after the delimiters -- and this can happen
regardless of delimiter:

if ( m|http://www.php.net|U ) # perl
if (preg_match('|http://www.php.net|U', $url) # PHP

if ( /http:\/\/www.php.net\//U ) # perl
if (preg_match('/http:\/\/www.php.net\//U', $url) # PHP

If you want more information on this, pick up a copy of "Mastering
Regular Expressions" or "Programming Perl", both from O'Reilly Press.

--
Matthew Weier O'Phinney | WEBSITES:
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