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5 months agoGood catch! Typo. Fixed.
No relation to the sports channel.
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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.
211·6 months agoMany Republicans are sponsored and bribed by fascist powers such as Putin’s Russia. They are under orders to take actions intended to weaken American industry, government, and society. This includes, for instance, sabotaging infrastructure projects, blocking disaster preparedness and relief, and fomenting political violence. The long-range goal is to make America incapable of projecting force to protect its international allies, global trade, etc.; a medium-range goal is to restore a regime broadly supportive of the international fascist movement.
(Just consider: Why does Putin support Trump? Putin doesn’t want to make America great; he wants to make America incapable — especially, incapable of defending Ukraine and, ultimately, other European allies. Putin predicts that Trump/Vance will accomplish that goal.)
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.)
C++ programmers always let their friends access their private members, so …
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.
I hear he lets all his friends access his private members.
Just be sure to pause for garbage collection occasionally.
I’m pointing at the architecture, not the specific implementation. Build something like Spanner, not something like a blockchain.
1a. I must have misunderstood the problem report.
1b. No wait, holy shit, how did this ever work!?2a. The director reminded us, at the last all-hands, that we should escalate to senior members of the team if we don’t know how to check our work.
2b. … yeah, they’re at Burning Man.3a. Remember, they knew I didn’t have a CS degree when they hired me. Dammit Jim, I’m a chemist, not a compiler engineer.
4a. It could be worse. I could be back in academia.
5a. There are more cute people in academia.
6a. HOW THE FUCK DID THE THREE-HOUR COMMIT QUEUE NOT CATCH THIS BUG BEFORE IT WAS PUSHED ON FRIDAY AFTERNOON?
6b. (looks up author of broken commit) Oh, we need to send more whiskey to that team on Friday mornings. That’d shut them up.7a. … yeah no, imma run the regression tests another time against an unchanged repo
7b. … resync and run them again
7c. … fuck, this is fucking voodoo but imma do it anyway WHY DID IT BREAK NOW8a. Wow, fixing that took, um, four actual bytes of delta?
8b. Everyone should slow the fuck down and see if they can fix all their bugs in four actual fucking characters of change to the actual fucking source code.
8c. What the fuck do I know. Megan committed 924 LOC last week that fixed lfile caching, and caught the btqmixer bug.9a. Sleeeeeeeep.
If you have a business asset, you can take out loans using that asset as collateral, and then use the loaned money to go do other business things. If you exaggerate the value of the asset, you can take out bigger loans.
(Even if you repay the loans later, you’ve taken advantage of the banks who made the loans, because they only have so much money to lend out to businesses.)
If you own real-estate, you owe property tax on it. If you understate the value of your real-estate, you can (for a while) get away with paying less in taxes.
Mr. Trump and his companies did both of these things. They exaggerated the value of their assets when it came time to get loans, and they understated the value of those same assets when it came time to pay taxes on them.
That’s its goal, not mine!
A game has a set of goals, and you can quit it without dying.
If there’s no set of goals, it’s not a game, it’s a toy.
If you can’t quit it without dying, it’s not a game, it’s real life.
(Does real life have a set of goals? Depends who you ask.)
5·2 years ago“Open source” in the sense this article uses is not really the same as “open source software” which is what this forum is about. Open source journalism does not refer to copyright license terms.
It’s not that TCP is a catch-all term, but “TCP/IP” is often used that way.
https://en.wikipedia.org/wiki/Internet_protocol_suite
The Internet protocol suite, commonly known as TCP/IP, is a framework for organizing the set of communication protocols used in the Internet and similar computer networks according to functional criteria. The foundational protocols in the suite are the Transmission Control Protocol (TCP), the User Datagram Protocol (UDP), and the Internet Protocol (IP).
For that matter, the classic networking text by Douglas Comer is Internetworking with TCP/IP and it does cover UDP, ICMP, ARP, DHCP, DNS, etc.
“What the user needed” / “What management demanded”