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I'm in the middle of Chapter 14, Perl-compatible Regular Expressions.

 

On Page 444, the following pattern is offered to test for presence of non-whitespace characters in a string:

 

^\S$

 

If I'm interpreting the chapter correctly so far, in the form created for testing subjects against patterns, pcre.php, I should enter this code inside a pair of delimeters, like so:

 

/^\S$/

 

So, I've done that, and typed a string into the subject text area:

 

Testing for whitespace characters.

 

I received FALSE, so far so good.

 

Then I type simply:

 

testing

 

And I received FALSE again!

 

Suspecting that I may have messed up the code of pcre.php, I replaced my file with the one I downloaded from Larry's website. Ran the same two tests again, received same results.

 

Either I'm missing something, which I suspect is the case, or the pattern is incorrect.

 

Could someone please explain to me how to make it work or what I'm doing wrong?

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Thanks, HartleySan - but do you mind if I ask for a little more detailed explanation?

 

First, I want to understand exactly what is this expression testing for. The presence of a single white space in the string, am I right?

 

So, if I test something like: 'test string' against this pattern, it should return TRUE, correct?

 

Or am I misunderstanding this?

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\s matches any whitespace character and \S matches any non-whitespace character, so ^\S$ matches a single non-whitespace character: a string that both begins and ends with \S. If you were to change it to ^\S+$, that would match one or more non-whitespace characters, meaning that "string" would be fine but "test string" would not.

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Hi Larry!

 

So, from your explanation I deduce that the queries that the pattern in question is describing a string that begins with a single non-whitespace character and ends immediately after that character.

 

So these strings should match the pattern: 'a', 'b', 'c', '-', '1', '`' --

 

-- and these shouldn't: 'aa', '2012', ' ', 'and so on'.

 

Did I get this right?

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