[RESOLVED] Regular Expressions - Allow X But Do Not Allow Y

cbj4074

I've searched far and wide on regular expressions and can find just about every example of what I would need, except one.

I'm trying to prevent users from entering the following characters:

" < > $ *

but I want users to be able to enter backslashes ().

I'm trying this:

ereg("^[^\"<>\$\*]*$", $input);

which, of course, works for the characeters I don't want to allow, but for reasons I can't discern, the expression also returns false whenever I add a backslash to the input string, even though I haven't specifically (to my knowledge) added a backslash anywhere in the expression (all backslashes are only used to escape special regex characters in the expression).

Why is this returning false when I add a backslash to the input string?

Thanks!

gammaster

Hi!
In your case there is no need for backslashes in the pattern. This will work:

ereg('^[^"<>$*]*$', $input);

cbj4074

Great! Thank you for the reply, gammaster.

I do, however, have a few more questions 🙂

1.) Why don't I need to escape the characters that are considered reserved in regex patterns (such as * and $, in this case)?

2.) Suppose I did want to use double-quotes around the pattern expression (for the sake of argument); how would I write the expression so that it still works?

3.) Suppose I wanted to allow all alphanumeric characters except z (and Z). How would I do that? I've tried grouping bracketed expressions and so forth, but that doesn't seem to work.

Thanks for all your time and help!

gammaster

Hi!
To answer first first:
I am not sure, but figured it out a couple of years a go and it works.. 🙂
If i should came with a qualified guess its because its in a bracket that describes legal or unlegal chars where the reserved chars don`t have the same meaning.

For your second question this should work:


$testString1 = 'test\\';
$testString2 = "test\\";

// Just backslash the quote that realy needs it.
$pattern = "^[^\"<>$*]*$";

echo ereg($pattern, $testString1) ? 'Test 1 is ok' : 'Test 1 failed';
echo '<br>';
echo ereg($pattern, $testString2) ? 'Test 2 is ok' : 'Test 2 faild';

And last:


$testString1 = 'hallo';
$testString2 = 'halloZ';
$testString3 = 'halloz';
$pattern    = '^[a-yA-Y0-9]*$';

echo ereg($pattern, $testString1) ? 'hallo is ok' : 'hallo isn`t ok';
echo '<br>';
echo ereg($pattern, $testString2) ? 'hallo big Z is ok' : 'hallo big Z isn`t ok';
echo '<br>';
echo ereg($pattern, $testString3) ? 'hallo small z is ok' : 'hallo small z isn`t ok';

Hope this works for you.

cbj4074

It does! Thanks for all your help and for taking the time to explain everything =)