No relation to the sports channel.
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“What the user needed” / “What management demanded”
3·8 months agoGood catch! Typo. Fixed.
Regex is good for a few very specific things, and sysadmins used to use it for goddamn everything. If all your server logs are in lightly-structured text files on a small number of servers, being able to improvise regex is damn useful for tracking down server problems. Just write a shell loop that spawns an
sshlogging into each server and runninggrepover the log files, to look for that weird error.These days, if you need to crunch production server logs you probably need to improvise in SQL and
jqand protobufs or systemd assmonkery or something.But if you actually need a parser, for goodness sake use a parser combinator toolkit, don’t roll your own, especially not with regex. Describing your input language in plain Haskell is much nicer than kludging it.
(This is the “totally serious software engineering advice” forum, right?)
Whatever you do, don’t get in a time machine back to 1998 and become a Unix sysadmin.
(Though we didn’t have CL-PPCRE then. It’s really the best thing that ever happened to regex.)
The answer given in the spoiler tag is not quite correct!
Test case
According to the spoiler, this shouldn’t match “abab”, but it does.
Corrected regex
This will match what the spoiler says:
^.?$|^((.)\2+?)\1+$Full workup
Any Perl-compatible regex can be parsed into a syntax tree using the Common Lisp package CL-PPCRE. So if you already know Common Lisp, you don’t need to learn regex syntax too!
So let’s put the original regex into CL-PPCRE’s parser. (Note, we have to add a backslash to escape the backslash in the string.) The parser will turn the regex notation into a nice pretty S-expression.
> (cl-ppcre:parse-string "^.?$|^(..+?)\\1+$") (:ALTERNATION (:SEQUENCE :START-ANCHOR (:GREEDY-REPETITION 0 1 :EVERYTHING) :END-ANCHOR) (:SEQUENCE :START-ANCHOR (:REGISTER (:SEQUENCE :EVERYTHING (:NON-GREEDY-REPETITION 1 NIL :EVERYTHING))) (:GREEDY-REPETITION 1 NIL (:BACK-REFERENCE 1)) :END-ANCHOR))At which point we can tell it’s tricky because there’s a capturing register using a non-greedy repetition. (That’s the
\1and the+?in the original.)The top level is an alternation (the
|in the original) and the first branch is pretty simple: it’s just zero or one of any character.The second branch is the fun one. It’s looking for two or more repetitions of the captured group, which is itself two or more characters. So, for instance, “aaaa”, or “abcabc”, or “abbaabba”, but not “aaaaa” or “abba”.
So strings that this matches will be of non-prime length: zero, one, or a multiple of two numbers 2 or greater.
But it is not true that it matches only “any character repeated a non-prime number of times” because it also matches composite-length sequences formed by repeating a string of different characters, like “abcabc”.
If we actually want what the spoiler says — only non-prime repetitions of a single character — then we need to use a second capturing register inside the first. This gives us:
^.?$|^((.)\2+?)\1+$.Specifically, this replaces
(..+?)with((.)\2+?). The\2matches the character captured by(.), so the whole regex now needs to see the same character throughout.
Once you learn about parser combinators, all other parsing looks pretty dopey.
You don’t kill zombies; a zombie is already dead. You wait for or reap zombies. (A zombie process is just a process table entry with its exit status; it goes away once the parent process has read that exit status.)
3435·11 months agoShow me what Stalinism looks like
This is what Stalinism looks like
C++ programmers always let their friends access their private members, so …
2·1 year agoIf you’re looking for commercial games on Linux, Steam has pretty much solved this with the “Steam Play” compatibility feature, which uses a customized version of WINE to run Windows games. For example, Baldur’s Gate 3 runs perfectly. It should work anywhere Steam does.
Ubuntu on Desktop I can understand.
Not anymore. A whole extra, unneeded, proprietary, locked-in package system. Ads in the default install.
There’s Mint, Pop!, and plenty of other options that actually respect the user.
Remember SOAP? Remember XML-RPC? Remember CORBA?
Those were not very good.
If you can’t tar to a pipe into ssh to a remote host and untar into an arbitrary location there, are you really using Unix?
I’m reminded of the character names that show up in MIT CS textbooks, like Alyssa P. Hacker (“a Lisp hacker”) and Eva Lu Ator.
There’s also the problem of some religious conservatives not realizing that straight people exist.
According to conservative psychologists like Paul Cameron or James Dobson, gay sex is a huge “temptation” that people must learn to resist; they worry that it would be the downfall of society if more people chose to succumb to that temptation. They might blame that temptation on Satan directly, or on LGBT+ propagandists, or liberalism; but they very much seem to believe that anyone could choose to be gay.
Sorry, no, that’s not how straight people work.
If you experience gay sex as a strong temptation, you’re just not straight. That’s okay! Quite a lot of people are straight, and are just not interested in having gay sex. If all the people who are “tempted” to have gay sex went and did so, there would still be lots of straight people left having lots of straight sex.
The odd part is that these conservative psychologists then teach this doctrine of “gay sex is a strong temptation for everyone” to an audience composed of mostly straight people.
If someone sells something to you and then takes it back later, that is theft.
1·1 year agoIt’s safe to look things up!
Looking up the name of a crime does not mean that you’re doing that crime.
If you look up “bank robbery” that doesn’t make you guilty of bank robbery. It doesn’t even mean you’re trying to rob a bank, or even want to rob a bank. You could want to know how bank robbers work. You could be interested in being a bank guard or security engineer. You could be thinking of writing a heist story. You could want to know how safe your money is in a bank: do they get robbed all the time, or not?
Please, folks, don’t be afraid to look up words. That’s how you learn stuff.
I hear he lets all his friends access his private members.
That jerk drank all my beer!