[SOLVED] newbie: disallow consecutive characters

[jcd]

Hello. I have a test script below:

 

$string = 'my test string';

$pattern = '/^[\w ]*$/';

echo preg_match($pattern,$string) ? 'GOOD string' : 'BAD string';

 

I wish for any occurances of 2 or more consecutive spaces to be a bad string.

 

ie:

 

'my test' = GOOD

'my test string' = GOOD

'my          test string' = BAD

 

I have tried lots of brackets and negation (^) but can't figure it out ???

 

Thanks.

[effigy]

/\x20{2,}/

 

Only spaces? What about whitespace in general (tabs, new lines)?

 

 

[jcd]

Yes I forgot about general whitespace, so I suppose the above regexp is now /\s{2,}/ ?

 

But the problem is that now "+" and "=" etc are allowed. I can't figure out how to combine above regexp with mine which only allows \w and single space characters.

[effigy]

You can run two separate patterns, or combine them: /\A(?:\w|\x20(?!\x20))+\z/

[jcd]

Thanks. I don't understand why it works though. I have some reading to do

[effigy]

NODE                    EXPLANATION

----------------------------------------------------------------------

  \A                      the beginning of the string

----------------------------------------------------------------------

  (?:                      group, but do not capture (1 or more times

                          (matching the most amount possible)):

----------------------------------------------------------------------

    \w                      word characters (a-z, A-Z, 0-9, _)

----------------------------------------------------------------------

  |                        OR

----------------------------------------------------------------------

    \x20                    character 32

----------------------------------------------------------------------

    (?!                      look ahead to see if there is not:

----------------------------------------------------------------------

      \x20                    character 32

----------------------------------------------------------------------

    )                        end of look-ahead

----------------------------------------------------------------------

  )+                      end of grouping

----------------------------------------------------------------------

  \z                      the end of the string

----------------------------------------------------------------------

[jcd]

Thanks, I haven't got to looking ahead yet, although I had heard of it.

 

What tool did you use to break down the regexp?

[effigy]

A Perl script:

 

use warnings;
use strict;
use YAPE::Regex::Explain;

my $regex = qr/\A(?:\w|\x20(?!\x20))+\z/;
print YAPE::Regex::Explain->new($regex)->explain();

[jcd]

Thanks once more.

 

It took some googling but the script works great