No relation to the sports channel.
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5·5 days agoOn the Internet, nobody knows you’re a dog … until you tell them.
201·5 days agoDo you remember the beginning of Trump’s previous term? His very first priority was to harm Muslims.
3·5 days 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?)
303·5 days agoYep. This is why online recipe sites put a whole goddamn personal essay before the actual recipe: if someone scrapes the page and copies it, they’ll scrape the (copyrightable) essay as well as the (non-copyrightable) recipe.
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.
314·8 days agoTry text.
Even in a home poker game, it is not possible for all the players to go home having made a profit, whereas that is very possible in the stock market due to growth, labor, and natural resources.
(The coal miner who gets a wage and black lung is not a player in the stock market. Neither is the sun, which provides free energy to agribusiness.)
In gambling, the house always wins, by extracting value from the players. In stock trading, the players (capitalists) collectively always win, by extracting value from labor, technological growth, and natural resources. These are not the same picture.
Sure, you can take on as much risk as you like using derivatives, and emulate a gambler using the stock market as a source of randomness (volatility). But that’s not how most traders behave, and it’s not how most traders’ payoffs work.
If someone doesn’t understand the difference between swearing at and swearing around, that’s a shitty environment.
In one of my better workplaces, the expression was “you can cuss the hardware, you can cuss the software, but don’t cuss your teammate.”
As the article mentions, Red Hat is IBM.
For what it’s worth, getting in the habit of making excuses for one’s use is part of alcoholism.
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