Mark Lee writes:
I have been reading about regular expressions. I am wondering why we need
"\\" in the pattern '/\\(:plant\\s*(.*?):\\)/e'? I know that "\(" means the
"(" character, but what does "\\(" mean? The extra "\" is also used before
"\s" and "\)". Is that part of pmwiki?
Peter has given you an excellent reply but it is even more complicated. PHP
doesn't remove all single backslashes, and a string wrapped in double quotes
quotes will have a different number of slashes stripped than the same string
wrapped in single quotes.
There is one thing which is the same in double and single quotes though: the
double backslash is always converted to a single slash. So it is really the
same for PHP in double and single quotes if all your backslashes are
doubled. So the following are correct
'/\\(:plant\\s*(.*?):\\)/e' and '/\(:plant\s*(.*?):\)/e' in single quotes
"/\\(:plant\\s*(.*?):\\)/e" only this one is correct in double quotes
(There is another difference between single and double quotes, in double
quotes $variables are expanded, in single they are not, so many times we
need to use the ones, many other times the others, and sometimes we could
use any, and sometimes we have and old string quoted one way, then we insert
a variable and need to change the quotes.)
So, some of us always escape the backslash, because this way we don't have
to remember if this is inside single or double quotes. This is easier to
write. This is what is in the PmWiki code.
If you look at some code examples or other programs, you'll see that other
people do it differently. I think that in the PHP manual on the website,
they always use single quotes because there are less characters and the code
is easier to read and probably easier to debug for beginners.
Both ways are correct, as long as your program does what you want. As a
programmer, you can decide how you work more efficiently.
Petko
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