Regular Expressions Ride Again 2

[acent]

Greetings,

I'm finally making a bold attempt at learning regular expressions. I've been reviewing the following:

http://www.codeproject.com/KB/recipes/regex2.aspx

When learning pattern searching it states:

Criteria: /[abcde]/ will match any single lowercase vowel.

Question: last I checked, b c and d were not vowles, so why would that match any lowercase vowel?

Further, it states

Criteria: /[^a-e]in]/

?An institute has posted guidance that protects against a reported vulnerability in all versions of software that could allow a Web site visitor to view secured content by using specially crafted requests to a Web server?.

[/quote]
Questions:
A. programming has taught me that every opening breacket must have a closing and vice versa. Does this not apply to regular expressions?
B. how does the s fall in between a-e?

Thanks for help on these.

"If it's stupid but works, it isn't stupid."
-Murphy's Military Laws

 

[feherke]

Hi

last I checked, b c and d were not vowles, so why would that match any lowercase vowel?

Of course, that will match any of the enumerated characters.

Posted: 25 May 2005

Please lower your expectations when reading old articles. ;-) Such ugliness happens especially with technical articles to become malformed due to careless rewriting of the site and batch modification of the texts.

I used to read the perlre. While the PHP documentation recommends the use of PCRE ( Perl-Compatible Regular Expressions ), most of that article is useful for PHP developers too. Not sure if it is suitable for your level. ( The perlrequick and perlretut tutorials and the perlfaq6 FAQ are also about regular expressions. )

Feherke.

http://rootshell.be/~feherke/

 

[jpadie]

so why would that match any lowercase vowel?

it won't. the author is a monkey. this is the regex for vowel matching

$pattern = '/[aeiouy]/';

take or leave the 'y' as you see fit.

to your questions

A. there is no need to close a bracket if you are trying to match only the opening bracket. however, programmatically, all brackets must be closed when used other than in their literal sense in a regex.

B. the pattern is matching every letter that is NOT a, b, c, d, e and that is immediately followed by the letters 'in' (case sensitive. therefore the sin of using will be matched. In this case the author is correct :

Negation in this context refers to everything not included in the listed character set is matched.

 

[acent]

Thank you feherke for the pointers to better tutorials.

Thanks jpadie for the clarifications. Yes, the author did state about the negation and for some reason I just didn't get it.

Thanks again!

"If it's stupid but works, it isn't stupid."
-Murphy's Military Laws