Talk:1638: Backslashes

Explain xkcd: It's 'cause you're dumb.
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It should be noted that this also occurs in almost every programming language where "\" is the escape character. i.e.

> Hello
> "Hello"
> \Hello\

Oh, and by the way, isn't this the third comic to mention "Ba'al, the Soul Eater"? Maybe we should start a category. (Others are 1246 (title text) and 1419.) 06:14, 3 February 2016 (UTC)

Did that before seeing you comment, so yes I agree. --Kynde (talk) 09:47, 3 February 2016 (UTC)
I don't think the regex is invalid

According to man grep you need to specify the -E option to use extended regex; without it unescaped parentheses are not interpreted, so they don't need to match.

My - very wild - guess is that it was the command he used to find the line with the most special characters, but I am not confident enough to edit the article (if someone can confirm?). (talk) (please sign your comments with ~~~~)

If it was supposed to do that, it doesn't work. Running it on my bash history matches no lines, and I have lots of special characters in there 07:12, 3 February 2016 (UTC)

Explain it to me like I'm dumb. What is this comic going on about? I think the explanation needs more examples like that hello, above, because that's almost understandable. -- 07:47, 3 February 2016 (UTC)

I agree. But I cannot help either.--Kynde (talk) 09:51, 3 February 2016 (UTC)

This is the third time Randall has mentioned Ba'al the Soul Eater xD International Space Station (talk) 08:26, 3 February 2016 (UTC)

Yes, that was already mentioned a few hours before you comment, see the first comment. --Kynde (talk) 09:51, 3 February 2016 (UTC)

After passing the regex through bash, you get \\[[(].*\\[\])][^)\]]*$ That is, the literal character \, followed by [ or (, followed by any number of any characters, followed by \, followed by ] or ), followed by any number of characters that aren't ) or ], until the end of the line. 08:33, 3 February 2016 (UTC)

It sounds like you know what you are talking about. Anyone who can explain it good enough for the explanation, and correct the explanation of the title text if it is wrong to say that it would not work. I have added this as the reason for incomplete. But maybe also examples are needed for people with not programming skills/knowledge. We also enjoy xkcd ;-) --Kynde (talk) 09:51, 3 February 2016 (UTC)

For fun:

cat ~/.bash_history | xargs -d "\n" -n 1 -I {} bash -c 'chars="$(echo "$1" | grep -o "[a-zA-Z0-9 ]" | wc -l)"; echo "$(( 100 - $(( $chars * 100 / ${#1} )) )) $1"' _ {} | sort -nrk 1 | less

Outputs your bash_history, ordered by relative gibberishness. This was copied by hand from desktop to mobile, might well have a few typos.-- 10:04, 3 February 2016 (UTC)

The problem in the comic is not with regexes per se but with situations when the entered text or expression passes through several interpreters, like bash -> grep/sed/awk, or program text -> external shell command. In such cases, you have to escape backslashes for each program in the sequence, and it gets worse if you have 'real' backslashes in the final text that you're processing with the utilities (Windows' file paths, for example). See Feel free to lift this to the explanation page, since I'm not good at longer and more careful explanations than this one. Also, gotta notice that Feedly stripped paired backslashes in the title text (probably passed it through some 'interpreter' embedded in its scripts). Aasasd (talk) 10:13, 3 February 2016 (UTC)

A funny comment about the MediaWiki software, which is even worse than this comic: <Nikerabbit> I looked the code for rlike and didn't find where it does this. Can you point me to it? <vvv> $pattern = preg_replace( '!(\\\\\\\\\\\\\\\\)*(\\\\\\\\)?/!', '$1\\/', $pattern ); <Nikerabbit> I thought that was ascii art :) (source) -- 10:18, 3 February 2016 (UTC)

Interestingly, I first looked at this on my phone (using Chrome Feedly for Android), but the title text did not display correctly in that the backslashes didn't appear (which was a little confusing!). In Chrome on my Windows desktop, the title text appeared correctly. Jdluk (talk) 11:36, 3 February 2016 (UTC)

enough with the harry potter fancruft. "elder" is a perfectly good word. just because you came across it for the first time in harry potter means you are *typing carefully* the kind of person that likes harry potter. unless this is a harry potter reference wiki, of course. in which case i'll prepare a complete list of every word that appears both here and there and put a list on every page. oh, right, no i won't. -- 12:41, 3 February 2016 (UTC)

Remember that "Elder" is used in a lot of RPGs to denote high level enemies or items. I feel like that's what Randall's referring to here, more than Harry Potter or the general sense of the term "Elder."

Attempting to add to the discussion: This regex is not necessarily invalid or incomprehensible. It looks like he was looking for a line with a regular expression or definitely some code. You just have to work your way through the backslashes. Although it might be invalid depending on the precise rules. He has some unescaped closing brackets and closing parenthesis. If these have to always be escaped then the regex is invalid. If however you don't have to escape a closing bracket with no opening bracket, then things are fine. I'm not familiar enough with grep's regex parser to know how it handles that edge case. Presuming those unescaped paren and brackets are fine, his regex searches for:

1. A backslash

2. An opening bracket

3. An opening parenthesis (this is a character set but the only character in it is an opening paren)

4. Any number of any characters

5. A backslash

6. An opening bracket

7. A closing bracket

8. A closing paren (presuming it doesn't have to be escaped when there is no opening paren)

9. A closing bracket (presuming it doesn't have to be escaped when there is no opening bracket)

10. Any number of character that are not a closing paren or closing bracket

11. The end of the line

Basically he is looking for a string that looks like:


Looks like a regex to me, and it looks like this regex also doesn't escape closing paren/brackets that don't have an opening paren/bracket, so I'm guessing that he knows what he is doing and his regex is fine. Maybe he was playing regex golf? Cmancone (talk)cmancone