(Useful) Stupid Regex Tricks?

careysb writes to mention that in the same vein as '*nix tricks' and 'VIM tricks', it would be nice to see one on regular expressions and the programs that use them. What amazingly cool tricks have people discovered with respect to regular expressions in everyday life as a developer or power user?"

Comments

IP and Hardware addresses

[rallymatte]

To filter a string to make sure it's a valid ip address this regexp is quite useful.
/^((25[0-5]|2[0-4][0-9]|1[0-9][0-9]|[1-9][0-9]|[0-9])\.){3}(25[0-5]|2[0-4][0-9]|1[0-9][0-9]|[1-9][0-9]|[0-9])$/

And this one for mac addresses
/^[0-9a-fA-F]{2}:[0-9a-fA-F]{2}:[0-9a-fA-F]{2}:[0-9a-fA-F]{2}:[0-9a-fA-F]{2}:[0-9a-fA-F]{2}$/

Re:IP and Hardware addresses

[Poltras]

So if I get this right, 0.0.0.0 is a valid ip address? I know the real regex would take a full post, but yes, it is possible to check with a single regex is it is valid, if it makes sense (127.0.0.1, 10.*, 169.254.*, etc etc) and if it's not a broadcast or a network address (not taking netmask into account).

Re:IP and Hardware addresses

[plumby]

So if I get this right, 0.0.0.0 is a valid ip address?

If you mean "Is it an address that you can send IP traffic to?", then the answer is no. If you mean "Is it a valid value that can end up in an IP address field (e.g., in the response to the ipconfig command)?" then the answer is yes - it means that you've not got a connection.

Re:IP and Hardware addresses

[kimba]

Why isn't 0.0.0.0 or 10.* a valid IP address? Since when is the definition of IP address to be unicast and globally routable?

I'd rather take issue with the fact it completely fails on IPv6 addresses.

Re:is it an rfc-822 compliant e-mail address?

[Timmmm]

Mmmmm readable.

use Regex::Common;

[oneiros27]

use Regex::Common qw(URI net);
$text_with_urls =~ m/$RE{URI}/;
$text_with_ips =~ m/$RE{net}{IPv4}/;

Re:99 Bottles of Beer on the wall

[Culture20]

(I would quote the final result but /. won't allow that many "junk" characters.. let's hope that doesn't cripple this entire discussion.)

Interesting that a site for nerds doesn't allow a lot of characters commonly used in source code.

Re:Mainframe Formatting

[msuarezalvarez]

You are a great candidate for the Useless Use of Cat award... specially endearing is your making a comment on the few commands your line uses :D

Re:Regexp-based address validation

[xenocide2]

The regex is beautiful in the sense that it lets you not be one of those assholes who refuses valid email addresses.

(Useful) Stupid useless articles

[Kent Recal]

Dear slashdot editors,

slashdot.org is not stackoverflow.com.
The articles and discussions here are not searchable in a sane way. Your recent attempts to mimic stackoverflow are just a waste of everybody's time because all those little tidbits that people post get lost in the internet noise immediately.

We know you're bit desperate for traffic these days. But this is not the way to go.

Re:email validation... FAIL

[jeremyp]

Your regex doesn't allow + signs in the name part.

Nor, I would suspect would it handle quoted strings e.g. "Jeremy P"@example.com is technically a valid RFC 822 address.

And having just looked up the RFC 5322 spec which you quote, I see there are more cases you fail to take acount of e.g.

Jeremy P <jeremyp@example.com>

Also, what makes you think upper case in domain names is invalid? jeremyp@example.COM fails validation.

Opposite

[Christopher_Olah]

IMHO, this is exactly the way that Slashdot should be going. Threads like this are interesting, add to the reservoirs of internet knowledge, and have the highest quality to noise ratios.

I (and I suspect many others) read Slashdot not for the latest +5 funny comment (though those can be fun to read) but to read the opinions of brilliant minds. And when those minds start trading secrets... Everyone wins.