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Posted by M Kinnear on 04/30/07 22:04
After posting (and less caffeine) I'd realised a few typos.
Cheers
"Toby A Inkster" <usenet200703@tobyinkster.co.uk> wrote in message
news:vsogg4-q7c.ln1@ophelia.g5n.co.uk...
>M Kinnear wrote:
>
>> I want to check a string only contains a-z 0-9 ( ) . and #
>>
>> I've used
>>
>> ereg("^[a-zA-z0-9().#]*)$"),$instr)
>
> Firstly, it looks to me like a couple of extra brackets slipped into the
> code you posted, as I don't think the above would parse at all. I'm
> assuming what you're actually using is:
>
> ereg("^[a-zA-z0-9().#]*$", $instr)
>
> Firstly, use preg_match. It runs faster that ereg; and ereg is being
> phased out in newer versions of PHP. This gives you:
>
> preg_match("/^[a-zA-z0-9().#]*$/", $instr)
>
> Now, the dot (.) in regular expressions has a special meaning. It means
> "absolutely any character you want". This means that you are allowing
> absolutely any character at all -- that is, your regular expression is
> doing nothing. The dot needs to be escaped with a backslash:
>
> preg_match("/^[a-zA-z0-9()\.#]*$/", $instr)
>
> Also, parentheses (these) have a special meaning within regular
> expressions, marking out subexpressions. IIRC, this shouldn't be a problem
> in your case because that special meaning disappears within square
> brackets. However, it doesn't hurt to escape them, and it looks a bit
> clearer to people just glancing at the expression:
>
> preg_match("/^[a-zA-z0-9\(\)\.#]*$/", $instr)
>
> Now try it.
>
>> Second q: is there clarification on whether characters need to be
>> escaped when part of a regex statement? i.e., should it be [$] or [\$] -
>> some websites/posts state they should be escaped, others say they
>> shouldn't
>
> Generally it never hurts to escape, so when something could go either way,
> err on the side of escaping things. Note that there are two levels of
> escapes coming into play here -- firstly as you're using "double quotes"
> you need to escape against PHP's built in string-parsing. Secondly, you
> need to escape against special meanings of characters in regular
> expressions.
>
> To make things simpler, it is usually preferable to use 'single quotes',
> so that you only have to worry about one set of escaping.
>
> preg_match('/^[a-zA-z0-9\(\)\.#]*$/', $instr)
>
> --
> Toby A Inkster BSc (Hons) ARCS
> http://tobyinkster.co.uk/
> Geek of ~ HTML/SQL/Perl/PHP/Python*/Apache/Linux
>
> * = I'm getting there!
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