[Resolved] front slash "/" in regular expression

meeiw

OK a very simple newbie question.

In some regular expessions see "/" in the beginning and the end of the pattern. In the documentation I have read "/" isn't a meta-character, but some examples in the manual uses "/" and it seems like it has som function anyway.

From the php-manual:

$html = "<b>bold text</b><a href=howdy.html>click me</a>";

preg_match_all ("/(<([\w]+)[^>]*>)(.*)(<\/\\2>)/", $html, $matches);

for ($i=0; $i< count($matches[0]); $i++) {
  echo "matched: ".$matches[0][$i]."\n";
  echo "part 1: ".$matches[1][$i]."\n";
  echo "part 2: ".$matches[3][$i]."\n";
  echo "part 3: ".$matches[4][$i]."\n\n";
}

pyro

You will see it at the beginning and end of ALL regexp. It indicates the beginning and ending of the regular expression literals. Basically, anything withing those two slashes is a regexp statement.

meeiw

Thanks for your fast reply!

But when I use eregi("^[a-z]+", $string) I don't use any front slashes, and I have seen a lot of examples of this on the web.
So, is this just a bad habit not to use the front slashes or must some other functions ,like preg_match_all, contain them?

pyro

If a regular expression doesn't contain delimiters, it is not a valid regexp. However, in PHP, you are able to user thing other than the / as a delimiter. Take a look at the introduction and examples at http://us2.php.net/pcre

laserlight

the difference would be between Perl compatible regex, e.g. preg_match(), and Posix type, e.g. ereg(), I think.

For the Perl compatible type patterns must have delimiters, usually "/"

meeiw

Thank you!
I was thinking that too, but I was not sure. It seems that the Posix have more coinstraints than PCRE. And right now its confusing a lot.

Why do you have to have double backslashes (\1) when you use back reference? (This is with the funtion preg_match_all() which uses PCRE)
In the manual all I can see is examples with a single backslash. Anyway when I changed my back reference from one to double backslashes it seems to work. Otherwise I don't know what I'm doing.

Heres the the pattern if anyone interessed,

"/^[^\[\]]*(\[(länk)\][^\[\]]*\[\/\\2\][^\[\]]*)*$/i"

which will validate the string

blaom[länk]ab aaaa a[/länk] g//g/hf g[länk]ab ag aa[/länk] sd fh dsf  sdfj dsfjh jh dsfj hdfs

stolzyboy

Originally posted by laserlight
why am i a junior member.....

go into your cp and change it

HalfaBee

You have to use \ in double quoted strings to get one \

eg "\" == '\'

So if you had "\1" you end up with '1'

HalfaBee

meeiw

Thanks a lot. I almost love you!

I have been sitting here in front of the computer all day long so I starting to get a little more slow than I usually am.
:p