What does this Regular Expression do

Question

$pee = preg_replace( '|<p>|', "$1<p>", $pee );

This regular expression is from the Wordpress source code (formatting.php, wpautop function); I'm not sure what it does, can anyone help?

Actually I'm trying to port this function to Python...if anyone knows of an existing port already, that would be much better as I'm really bad with regex.

Answer 1

The preg_replace() function - somewhat confusingly - allows you to use other delimiters besides the standard "/" for regular expressions, so

"|<p>|"

Would be a regular expression just matching

"<p>" 

in the text. However, I'm not clear on what the replacement parameter of

"$1<p>" 

would be doing, since there's no grouping to map to $1. It would seem like as given, this is just replacing a paragraph tag with an empty string followed by a paragraph tag, and in effect doing nothing.

Anyone with more in-depth knowledge of PHP quirks have a better analysis?

Answer 2

wordpress really calls a variable "pee" ?

I'm not sure what the $1 stands for (there are no braces in the first parameter?), so I don't think it actually does anything, but i could be wrong.