4 ms·
I once argued that it `could not be so hard to write a regexp that validates Debian package versions`. Ohboy. Let's just say that in the end it became a point o
by mioelnir 11y ago
I once argued that it `could not be so hard to write a regexp that validates Debian package versions`. Ohboy. Let's just say that in the end it became a point of pride to come up with something.
Debian package version numbers have leading and trailing optional parts and if they are specified, then the characters used as separator of these parts are allowed as part of the version number.
The resulting regexp ended up being essentially four different regexp expressions with four leading conditions utilizing look-ahead and look-behind matching to select which inner regexp to use. It was sufficiently beyond actually regular, even if supported by modern RE tools.
And this is a common pattern in my experience. If you frequently need look-ahead or look-behind, you are often past something you should reasonably disassemble using regexp and should instead start defining a grammar and parse the input stream against it.
- paulddraper 11y agoThe Debian version format was not made to be easy. https://www.debian.org/doc/debian-policy/ch-controlfields.html#s-f-Version https://www.debian.org/doc/debian-policy/ch-controlfields.ht... But in any case, this works. ^(\d+:|(?!.*:))(?!.*-[^-]*:[^-]*$)\d(-?[A-Za-z0-9.+:~])*$ Actually, I think I variable-width lookbehind might be handy here to check the hyphens, but I don't have Chrome 49, so I'll forgo it.
- mioelnir 11y agoI'd contend that it was "made" at all. When I first looked at the relevant section of the policy manual, my takeaway was that they had a script that iteratively removed the leading and trailing optional fields, making use of the separators safe only if the fields were there so the script did not misfire. They then took the runtime behavior of that existing script and called it the standard.