explain xkcd - User contributions [en]

2002: LeBron James and Stephen Curry

2021-10-28T17:34:14Z

162.158.255.117:

{{comic
| number = 2002
| date = June 4, 2018
| title = LeBron James and Stephen Curry
| image = lebron_james_and_stephen_curry.png
| titletext = The 538TR attempts to capture a player's combined skill at basketball (either real-life or NBA 2K18) and election forecasting.
}}

==Explanation==
At the time of this comic, the {{w|2018 NBA Finals}} were going on, between the {{w|Cleveland Cavaliers}} and the {{w|Golden State Warriors}} with the Warriors leading 2 games to 0 in a best of seven series. At first glance, the comic looks like an in-depth analysis of two of the star players on those teams, {{w|LeBron James}} and {{w|Stephen Curry}}. The joke is that while comprehensive, all the statistics are completely meaningless - many of them are obviously false, and many don't show any correlation, and if there is one, it's extremely unlikely there is any causal link in there.

The first graph includes a nine-digit {{w|Social Security number}} issued for US citizens which is typically not considered a metric related to athletic ability. As Social Security numbers are essentially random numbers ([https://www.ssa.gov/employer/randomization.html until 2011], there was a geographic correspondence for the first three digits), the graph shows only the {{w|free throw}} percentage of a large number of players, artificially spread vertically. Also note that Social Security numbers are not usually made public, barring security leaks.

The second graph is a graph of 2018 points per game vs teammate's APGAR score. {{w|APGAR score}} is used to quickly summarize the health of newborn children, with scores of 7 and above indicating an infant has generally normal health; its use to rank adult NBA players is odd, if not improper. This graph indicates LeBron's teammates have an average APGAR score of approximately 2.1. Scores of 3 and below are generally regarded as critically low and possibly requiring medical attention. Low APGAR scores can also be associated with increased risk of neurological disorders such as cerebral palsy. The joke appears to be in giving LeBron's less-than-impressive teammates a low APGAR score.

The shot map shows from what position Curry's shots were scored compared to other NBA players. This references Stephen Curry's propensity to take (and make) shots from well beyond the normal distance required for 3 points.[https://thebiglead.com/2016/02/26/stephen-currys-shooting-percentage-from-28-feet-out-is-mind-boggling/] The comic then takes this to hilarious extremes by showing he supposedly scored several times from outside the playing field (not a legal play), including twice from the {{w|bleacher}}s (''definitely'' not a legal play), and once from the {{w|locker room}} (which is physically impossible due to multiple walls in between{{Citation needed}}).

Next is a graph of (team) win percentage vs sandwiches eaten during play. Average win percentage seems to go down as number of sandwiches eaten goes up to 3. It does indicate that the Golden State Warriors still have quite high win rate even though they have eaten either 4 sandwiches per game, or 4 sandwiches total during games, over the course of the 2018 season (the graph is unclear on this point). Golden State Warriors seem to be an outlier as their win percentage is much higher than the one of the teams that have eaten 2-3 sandwiches.

In the "2018 total points" table, the highlighted {{w|Golden State Warriors}} and {{w|Cleveland Cavaliers}} represent the teams of Stephen Curry and LeBron James respectively. {{w|Magnetic north}} is the south pole of the {{w|Earth's magnetic field}}. Certain animals use the magnetic field to navigate and align themselves (including migratory birds, bees, and foxes), but there is no evidence that humans are affected by the earth's magnetic field. This means that there should not be any correlation between orientation of a basketball court and points scored. But Cleveland Cavaliers have a much a higher percentage of goals scored when orientation is towards magnetic North than other teams, probably it is implied that LeBron James and/or his team somehow actually senses magnetic field and uses that to direct shots, but more likely explanation would be that it is just the orientation of the court during their home games.

The title text is a continuation of the joke in the bottom table. {{w|FiveThirtyEight}}, sometimes referred to as 538, is a website that focuses on opinion poll analysis, politics, economics, and sports blogging.

The table at the bottom includes more unrelated comparisons:

;Have You Heard of Him
: Although both players are well known in their native United States, elsewhere basketball is considered a minority sport. Of the 7 billion people in the world it is likely that less than 2% {{Dubious}} of the total population will have heard of either player.{{Citation needed}} According to Randall, LeBron James is a more well known player than Stephen Curry.
;President During Most Recent Game 7 Loss
: In the NBA, the top 16 teams qualify for a single elimination play-off to determine the season champion, with each series played as a {{w|Playoff_format#Best-of-seven_playoff|best-of-seven}} series (first to win 4 games). After the fourth game, fixtures are only played as required. Most fixtures are therefore resolved before the last game. Lebron James has participated in seven playoff game 7s in his career (winning 5 of 7), and the last time his team lost a game seven was on May 18, 2008 ({{w|George W. Bush}} was still President). This also highlights that James is an older athlete, yet has been fairly dominant through his career. Stephen Curry's last game 7 loss came at the hands of Lebron James in the {{w|2016 NBA Finals}} ({{w|Barack Obama}} was President). It is notable that both the Golden State Warriors and Cleveland Cavaliers won their respective games 7 in their Conference Finals to make it to this year's NBA Finals.
;Pog Collection
: {{w|Milk caps (game)|Pogs}} were a {{w|fad}} in the 1990s. It is unclear why James would have a "staggeringly large" collection of pogs, besides being 4 years older than Curry.

;Career Average Fed Interest Rate
:The Federal Interest Rate, or {{w|federal funds rate}}, is an interest rate set by the {{w|United States Federal Reserve}}. This rate is increased or decreased periodically based on the health of the U.S. economy. As of the time of publishing, the federal interest rate was targeted at 1.75%. The rate has fluctuated from a high of around 5% to a low of near 0% (during the time of the {{w|Great Recession in the United States|2008 recession}}). James' career average federal interest rate is higher than Curry's, because James began his career before Curry, when interest rates were higher.
;Name Scrabble Score
:Both "lebronjames" and "stephencurry" are worth 22 points in {{w|Scrabble}}, however both being names are not recognized as scorable words and would be worth nothing.
;Best Sport
: It is claimed that their best sport is basketball. However, although they have chosen basketball as a career, this does not mean they were not better at a sport that does not offer a professional career. On the other hand with amount of training they did in basketball, it is extremely likely that basketball is the best sport for both of them at the moment.
;Height
: Both are listed as over 6 feet tall, which is not at all unusual for professional basketball players. Stephen Curry is 6'3" and LeBron James is 6'8", although this chart does not distinguish the exact heights. In most contexts, bucketing humans into broad height-groups would be unsurprising, but in basketball more detail is relevant. Thus, the information is accurate but uninformative --- like the rest of the data in this comic.
;Retirement Year
: In 2027, Stephen Curry will be 39 years old, which is a typical retirement age for NBA players. LeBron James's retirement age is listed as ''Unknown''.
: This may refer to James's high level of play through his mid-30s, when typical players have a decline in their performance.{{Citation needed}}
;FiveThirtyEight Total Rating
: {{w|Nate Silver}} is a political commentator and founder of the website {{w|FiveThirtyEight}}, which uses and promotes statistical approaches in explaining the world. The site's two major areas of focus are in politics (especially on elections - it became famous for correctly predicting for whom 49 of 50 states would vote in the 2008 US presidential election and every US state in the 2012 election, and though it wasn't as accurate in 2016 it had given Donald Trump a larger chance of Electoral College victory than other mainstream media sources) and sports (Silver first got into statistical analysis via baseball). The presence of both sports-related and politics-related topics in the comic, however related they are (or not) with each other, seems to be a nod towards FiveThirtyEight's content.
: Nate Silver has a much higher 538TR than either Curry or James. As explained in the title text, the 538TR combines basketball skill (either real-life or video game basketball) with election forecasting. This could suggest that Silver is proficient at basketball, presumably the video game kind, or else that election forecasting is heavily weighted.

==Transcript==
{{incomplete transcript|Do NOT delete this tag too soon.}}
:'''NBA Playoffs ''DataDive'' '''
:'''LeBron James and Stephen Curry'''
:'''What makes these superstars so extraordinary?'''

:[The comic consists of several plots and tables, listed here from top to bottom, left to right.]

:'''Scatter plot of Social Security number vs Free throw percentage'''
:[Social Security numbers range from 000-00-0000 to 999-99-9999. No pattern discernable, aside from points being a bit denser in the middle of the plot. Stephen Curry is marked as a point on the right edge of the plot, corresponding to a high free throw percentage.]

:'''Scatter plot of 2018 points per game vs Average teammate APGAR score'''
:[APGAR scores range from 0 to 10. Pattern suggests a somewhat positive link between the two factors. LeBron James is marked as having a lot of points, but a low teammate APGAR score of approximately 2.1.]

:'''Shot map'''
:[Legend: grey dot for all players, black dot for Stephen Curry]
:[A diagram of a basketball court is shown with dots placed where players have taken shots at the goal. For the all players category the dots generally cluster next to the goal basket and in front of the three point line. Stephen has 3 dots next to the basket (one is behind it), but does cluster next to the three point line. He also has several dots on the other side of the playing field, and outside it, including three in the bleachers and one in the locker room.]

:'''Sandwiches eaten during play vs Win %'''
:[Sandwiches eaten range from 0 to 4. A plot that suggests no relation between the factors because practically all dots are in the zero sandwiches column. 2018 Warriors have one dot at around 60% and 4 sandwiches.]

:'''2018 total points'''
:[A table listing teams and their points overall and "When net is within 15° of magnetic north". The rows for the Golden State Warriors and the Cleveland Cavaliers are highlighted, the latter showing an abnormally high score in the magnetic north column.]

:{| class = "wikitable"
! 2018 total points
! Overall
! When net is within 15° of magnetic north
|-
|'''Golden State Warriors'''
|'''9304'''
|'''330'''
|-
|Houston Rockets
|9213
|268
|-
|New Orleans Pelicans
|9161
|219
|-
|Toronto Raptors
|9156
|341
|-
|'''Cleveland Cavaliers'''
|'''9091'''
|'''1644'''
|-
|Denver Nuggets
|9020
|280
|}

:[A table at the bottom:]

:{| class = "wikitable"
!
! Stephen Curry
! LeBron James
|-
|Have you heard of him
|Probably
|Yes
|-
|President during most recent game 7 loss
|Obama
|Bush
|-
|Pog collection
|Large
|Staggeringly large
|-
|Career average Fed interest rate
|3.42%
|4.41%
|-
|Name Scrabble score
|22
|22
|-
|Best sport
|Basketball
|Basketball
|-
|Height
|Over 6'
|Over 6'
|-
|Retirement year
|2027
|Unknown
!Nate Silver
|-
|FiveThirtyEight total rating (devised by Nate Silver to combine all metrics into a single stat)
|'''37.4'''
|'''31.8'''
|'''86.6'''
|}

==Trivia==
This comic was posted the day after the second game in the 2018 NBA Finals between the Golden State Warriors (Stephen Curry's team) and the Cleveland Cavaliers (LeBron James' team). It is the fourth consecutive time the two teams faced each other at the finals, which is unprecedented in major sports leagues in North America. The Warriors won in 2015 and 2017, the Cavaliers won in 2016. At the time of the comic, the Warriors led the current series 2-0; which they eventually won.

{{comic discussion}}

[[Category:Sport]]
[[Category:Basketball]]
[[Category:Comics featuring Nate Silver]]
[[Category:Politics]]
[[Category:Statistics]]

Talk:828: Positive Attitude

2016-03-04T18:16:09Z

162.158.255.117:

What is an IV instrument? It has to be explained. --[[User:Dgbrt|Dgbrt]] ([[User talk:Dgbrt|talk]]) 20:58, 30 November 2013 (UTC)

I've rewritten all the explanation, expanding it a bit, adding the title text part and the IV explanation. So I've also removed the incomplete tag. Hope it can be now considered "complete". [[Special:Contributions/173.245.53.117|173.245.53.117]] 02:49, 5 December 2013 (UTC)

I can't believe no one has mentioned the INT, CON and CHR stats on the monitor {{unsigned|CardaStcol}}

Maybe the Cueball on the bed is Megan after chemo (and associated hair loss )?

In related comics there is usually a Megan and Cueball character. Some whould say the personality is a little off to be Megan and fits Cueball better. [[Special:Contributions/162.158.255.117|162.158.255.117]] 18:16, 4 March 2016 (UTC)

Talk:1638: Backslashes

2016-02-04T01:26:09Z

162.158.255.117: oops... forgot a **forward** slash :P

...Maybe it's meant to search for all Game Grumps transcripts which make mention of the "[http://gamegrumps.wikia.com/wiki/Grep Grep]" gag? [[Special:Contributions/108.162.216.55|108.162.216.55]] 15:53, 3 February 2016 (UTC)

It should be noted that this also occurs in almost every programming language where "\" is the escape character. i.e.
print("Hello")
> Hello
print("\"Hello\"")
> "Hello"
print("\\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 [http://www.explainxkcd.com/wiki/index.php/1246:_Pale_Blue_Dot 1246] (title text) and [http://www.explainxkcd.com/wiki/index.php/1419:_On_the_Phone 1419].)
[[Special:Contributions/173.245.54.29|173.245.54.29]] 06:14, 3 February 2016 (UTC)
:[[:Category:Ba'al|Did that]] before seeing you comment, so yes I agree. --[[User:Kynde|Kynde]] ([[User talk:Kynde|talk]]) 09:47, 3 February 2016 (UTC)

The last entry may also be an oblique reference to the infinitely-expandable recursive acronym "GOD = GOD Over Djinn" mentioned in Richard Hofstadter's Gödel, Escher, Bach.[[User:Taibhse|Taibhse]] ([[User talk:Taibhse|talk]]) 16:42, 3 February 2016 (UTC)

;I don't think the regex is invalid

According to <tt>man grep</tt> you need to specify the <tt>-E</tt> 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?). {{unsigned ip|141.101.66.83}}

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 [[Special:Contributions/197.234.242.243|197.234.242.243]] 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. --[[Special:Contributions/198.41.238.231|198.41.238.231]] 07:47, 3 February 2016 (UTC)
:I agree. But I cannot help either.--[[User:Kynde|Kynde]] ([[User talk:Kynde|talk]]) 09:51, 3 February 2016 (UTC)

This is the third time Randall has mentioned Ba'al the Soul Eater xD [[User:International Space Station|International Space Station]] ([[User talk: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. --[[User:Kynde|Kynde]] ([[User talk:Kynde|talk]]) 09:51, 3 February 2016 (UTC)

After passing the regex through bash, you get <nowiki>\\[[(].*\\[\])][^)\]]*$</nowiki> 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. [[Special:Contributions/108.162.216.44|108.162.216.44]] 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 ;-) --[[User:Kynde|Kynde]] ([[User talk: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.--[[Special:Contributions/162.158.90.208|162.158.90.208]] 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 https://en.wikipedia.org/wiki/Leaning_toothpick_syndrome.
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). [[User:Aasasd|Aasasd]] ([[User talk:Aasasd|talk]]) 10:13, 3 February 2016 (UTC)

:A funny comment about the MediaWiki software, which is even worse than this comic: <code><nowiki><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 :)</nowiki></code> ([https://phabricator.wikimedia.org/P110$275 source]) --[[Special:Contributions/162.158.91.215|162.158.91.215]] 10:18, 3 February 2016 (UTC)

Interestingly, I first looked at this on my phone (using <strike>Chrome</strike> 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. [[User:Jdluk|Jdluk]] ([[User talk:Jdluk|talk]]) 11:36, 3 February 2016 (UTC)

enough with the harry potter fancruft. "elder" is a [[Wiktionary:elder|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. --[[Special:Contributions/141.101.106.161|141.101.106.161]] 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."
: +1. Between the fact that harry potter (, ages, or tribes) aren't mentioned anywhere else in the text and the comic being a progressive list, I see this being the most likely explanation. Plus the metion of demons, which are easily the most* common usage of the modifier.
:: (*) or second most, after "elder gods", who are, let's face it, also demons. [[Special:Contributions/162.158.180.125|162.158.180.125]] 14:41, 3 February 2016 (UTC)
::: I'm pretty sure that "Elder backslash" is in reference to the "Elder gods" of Lovecraft. [[Special:Contributions/173.245.54.35|173.245.54.35]] 16:51, 3 February 2016 (UTC)
:::: Note also that it's called 'The Elder Wand' not as an intensifier, as in this comic and the other examples given, but because it is literally ''made from the wood of an [https://en.wikipedia.org/wiki/Sambucus_nigra Elder Tree]'' I'm pretty sure it's not an intentional reference. -Graptor [[Special:Contributions/173.245.54.23|173.245.54.23]] 19:29, 3 February 2016 (UTC)

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:

\[(AAAAA\[])]AAAAA

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?
[[User:Cmancone|Cmancone]] ([[User talk:Cmancone|talk]])cmancone

Ninjaed by Cmancone, above. I agree with that result in every respect except for the start-of-string being potentially anything, but putting my own analysis in here because it took long enough to type!
Depth-of-backslash might depend upon depth of utility. In Perl, <nowiki>''</nowiki>-quotes (among others) treat everything within as literal whilst ""-quotes (and variations) interpolates any special characters, variables, etc that you put in it. (Search for "Quote and Quote-like operators" in your favourite PerlDocs source.) '\sss' is a literal backslash followed by three 's' characters , while "\sss" is the special \s escape (a whitespace) followed by two further regular characters. You might need to define the first when you need to use it to provide a not-previously-escaped \s so that it might be escaped within another context. ''Or'' you define it as "\\sss" (escaped-\) the first time, as equivalent to '\sss'. But '\\sss' would be a literal that, later, could be interpreted as an escaped-\ to the input of a further context where the \s finally becomes 'match a whitespace'.

'\\\sss' would be literal, whilst "\\\sss" could be equivalent to '\ ss' (literal backslash, literal space, rest of characters). Then, instead of literal '\\sss', for some purpose, you could interpolate two escaped-backslashes "\\\\sss"... and so on.

Meanwhile I ''think'', just from visual inspection, "'''\\\[[(].*\\\[\])][^)\]]*$'''" in Bash should obey the interpolation rules quite nicely. The first two characters must be a literal backslash (from the escaped-backslash) and a literal open-square bracket (again, escaped). The next open-square and the close-square shortly after depict a character class that contains only an open-parenthesis, and could have been written as '''$'''.

The '''.*''' indicates zero-or-more (the asterix) instances of ''any'' character (the dot). There is then a literal backslash (from the next '''\\''' duo) and a literal open-square (the '''\[''' pair) and close-square (the '''\]''' pair). The ''')''' is literal and does not need escaping (as a parenthesis group had not yet been opened), as is the next ''']''' character. To be sure, I would have written these two as the pair escapes '''$\]''', but horses for courses...

Then there's another character class (the next '''[''' and the final ''']''') required zero-or-more times (the asterix) to use up all the rest of the characters to the end (the ending '''$''' character). As there was no '''^''' character (a.k.a. caret/circumflex/etc) at the start, the match isn't bothered about what unmatched characters appear before the original '''\('''. This character class, however, starts with a '''^''' which in this context (the very first character of a character-class definition, not somewhere where an entire match-string starts) indicates negation of the following selection, so it is all characters ''but'' those specified, which is the regular close-parenthesis and (because it needs to be contained within a '''[]''' pair) the escaped close-square.

So, all matching strings must start with '''\[(''', i.e. the backslash, open-square and open-paren. They can continue with ''any'' further text, before then having a '''\[])]''', i.e. backslash, open-and-close-squares and close-paren, close-square. After this, the match continues just as long as there are no non-closing square/classic brackets before the ending.

The minimum matching literal string would be '''\[(\[])]''' with longer variants being of the form '''X\[(Y\[])]Z''' where X and Y can be replaced by anything (or be absent), and Z can be replaced by anything (or absent!) ''so long as it doesn't contain possibly relevent close-brackets!''. The latter stipulation is likely because the Y (and X) ''is'' allowed to contain these characters, and for some reason you don't want to confuse the test by finding some other '''\[])]''' segment within the X/Y-zones. (In this context, it doesn't actually seem to matter too much. But it might do in ways I haven't spotted or just be a hang-over from a prior permutation of the test.)

The "grep -o" function is working on the output to the file being '''cat'''ed (there are alternate ways of doing this that some people might prefer), to only accept the lines in the file that match the '''X\[(Y\[])]Z''' string. These lines would appear to be lines of out.txt (a fairly generic name that reveals little to its original purpose) that are well-formed for some other purpose. A safety-escaped (i.e. not to be taken literally by any simple parser) '''[]'''-grouping containing a '''()'''-group (''not'' escaped, perhaps reasonably in context) containing potentially random text followed by an empty '''[]''' pair (again, safety-escaped). Depending on the source, the empty '''[]'''-pair could mean many things, as with the other layers. And the lines may end with any further text.

The "out.txt" file might be the result of a prior Grep (string-search function) quote possibly scanning code for lines of particular importance by another pattern and dumping the results to out.txt for further perusal. And then Randall finds the need to dig further into the first result by extracting just those already selected that all have the '''X\[(Y\[])Z]'''-ish pattern to them.

But I could be wrong, and that's way too long for an official explanation.
(Perhaps just something like the penultimate paragraph, if we're not entirely mistaken?) [[Special:Contributions/162.158.152.89|162.158.152.89]] 14:14, 3 February 2016 (UTC)

The regex is supposed to be looking for:
\\\ backslash
[[(] [ or (
.* any character (repeated 0 or more times)
space space
\\\ backslash
[[\])] probably meant to match either [, ] or ). However, it's not correct, it instead matches the literal characters [)]
[^)\]]* probably meant to match any character that isn't ) or ], repeated. Instead it means one character that's not a ), and then a ] zero or more times
$ end of string

The first problem is that you're not supposed to escape ] in a [...], and it also has to be first in the grouping (unless negated with a ^) It should be [][)] or something similar.
The second problem is the same. The last bit should be [^])]*$ and not [^)\]]*$. [[User:Khris|Khris]] ([[User talk:Khris|talk]]) 14:24, 3 February 2016 (UTC)

I was reading through the regex, if using grep you run into an error with an unmatched ")". Removing this gets a string such as \[(AAAAA\[]]AAAAA$ http://regexr.com/3cng8 [[Special:Contributions/162.158.214.230|162.158.214.230]] 14:42, 3 February 2016 (UTC)

The regex relies on several special cases (*surprise*).
First: bash double-quote expansion (see [https://www.gnu.org/software/bash/manual/html_node/Double-Quotes.html#Double-Quotes]). Perhaps non-intuitively, \\\ followed by a character that \ doesn't escape is an escaped backslash followed by a literal backslash, effectively the same as \\\\ followed by that same non-escaped character. After bash double-quote expansion, this results in:

\\[[(].*\\[\])][^)\]]*$

grep interprets this as:

# any leading non-\ characters
# literal backslash
# character class containing [ and (
# zero or more *any* characters
# another literal backslash
# yet another literal backslash, via a character class containing only a backslash. Note this does not contain an escaped ], as it might appear at first glance. See [http://www.gnu.org/software/grep/manual/html_node/Character-Classes-and-Bracket-Expressions.html]
# literal )
# literal ]
# character class of anything except ), \
# zero or more ]
# end of line

Matching examples:
*echo 'asdf\[asdfasdf\\)]a]]]]]]' | grep -o "\\\[[(].*\\\[\])][^)\]]*$"
*echo '$\$]P' | grep -o "\\\[[(].*\\\[\])][^)\]]*$"

One key thing to understand is that \ is not a special character when it's in a bracket expression - you can't escape characters in bracket expressions. So [^)\] simply means any character other then ) or \. Also, ( and ) are just regular characters unless they are escaped in basic regular expressions - extended regular expressions reverse this rule.
----
[[Special:Contributions/108.162.216.34|108.162.216.34]] 16:14, 3 February 2016 (UTC)rb

I don't know about the regular expression in the title text, but I think the explanation is incorrect in that it starts off talking about regular expressions. Escaping backslashes is an issue with strings in programming in general. [[Special:Contributions/173.245.54.46|173.245.54.46]] 17:12, 3 February 2016 (UTC)
----
I suspect that Randall may have used the regexp in the title text to *find* malformed regular expressions in a file (out.txt) that he (or someone) had previously filled with output from some error message (or collection of error messages, or at least the output of something where a regular expression had been expected to work but had not worked as expected). [[Special:Contributions/162.158.252.227|162.158.252.227]] 19:06, 3 February 2016 (UTC)

You can use metacharacters in character classes, the only metacharacters in a character class that must be escaped are the closing square bracket (]), the backslash (\), the hyphen, and the carat and hyphen (^) if they are the first listed item in the set. The closing square bracket requires escaping because including it without would signal the end of the set otherwise, which then means the backslash must also be escaped. The hyphen must be escaped because, without it, it signals a range (unless it is listed first, then it is literal without escaping). Carat when listed first because otherwise it signals a negative set. 
Therefore, the end of the title text regex matches a backslash followed by either ] or ), which is then followed by any number (including none) of characters so long as they are not ] nor ) which means the whole regex can match "\[something\] more" or "$something$more" or "\[something\) more" as well as "\[something\]". — [[Special:Contributions/162.158.255.117|162.158.255.117]] 01:16, 4 February 2016 (UTC)

I'll add that I use an ''almost identical'' regex in my mail server for matching mailing-list subject lines which often have a format of "[Listname] normal subject line" which made it pretty recognizable to me. — [[Special:Contributions/162.158.255.117|162.158.255.117]] 01:24, 4 February 2016 (UTC)

== Example of a match ==

First, the shell will do some escaping substitution. So, in order to easily read it, let's see what grep really receives:

$ echo "\\\[[(].*\\\[\])][^)\]]*$"
\\[[(].*\\[\])][^)\]]*$

Let's break it out:

* <code>\\</code> matches a <code>\</code>
* <code>[[(]</code> matches either a <code>[</code> or a <code>(</code>
* <code>.*</code> matches any series of characters until the next match
* <code>\\</code> matches a <code>\</code>
* <code>[\]</code> matches a <code>\</code>
* <code>)]</code> matches <code>)]</code>
* <code>[^)\]</code> matches anything but <code>)</code> or <code>\</code>
* <code>]*</code> matches any number of <code>]</code> (including none)
* <code>$</code> matches the end of the string

So the string '''\[aaa\]\\)]a]]]]]]''' matches!

Talk:1638: Backslashes

2016-02-04T01:24:41Z

162.158.255.117: adding that I use almost identical regex in mail server, so recognized it right away

...Maybe it's meant to search for all Game Grumps transcripts which make mention of the "[http://gamegrumps.wikia.com/wiki/Grep Grep]" gag? [[Special:Contributions/108.162.216.55|108.162.216.55]] 15:53, 3 February 2016 (UTC)

It should be noted that this also occurs in almost every programming language where "\" is the escape character. i.e.
print("Hello")
> Hello
print("\"Hello\"")
> "Hello"
print("\\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 [http://www.explainxkcd.com/wiki/index.php/1246:_Pale_Blue_Dot 1246] (title text) and [http://www.explainxkcd.com/wiki/index.php/1419:_On_the_Phone 1419].)
[[Special:Contributions/173.245.54.29|173.245.54.29]] 06:14, 3 February 2016 (UTC)
:[[:Category:Ba'al|Did that]] before seeing you comment, so yes I agree. --[[User:Kynde|Kynde]] ([[User talk:Kynde|talk]]) 09:47, 3 February 2016 (UTC)

The last entry may also be an oblique reference to the infinitely-expandable recursive acronym "GOD = GOD Over Djinn" mentioned in Richard Hofstadter's Gödel, Escher, Bach.[[User:Taibhse|Taibhse]] ([[User talk:Taibhse|talk]]) 16:42, 3 February 2016 (UTC)

;I don't think the regex is invalid

According to <tt>man grep</tt> you need to specify the <tt>-E</tt> 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?). {{unsigned ip|141.101.66.83}}

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 [[Special:Contributions/197.234.242.243|197.234.242.243]] 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. --[[Special:Contributions/198.41.238.231|198.41.238.231]] 07:47, 3 February 2016 (UTC)
:I agree. But I cannot help either.--[[User:Kynde|Kynde]] ([[User talk:Kynde|talk]]) 09:51, 3 February 2016 (UTC)

This is the third time Randall has mentioned Ba'al the Soul Eater xD [[User:International Space Station|International Space Station]] ([[User talk: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. --[[User:Kynde|Kynde]] ([[User talk:Kynde|talk]]) 09:51, 3 February 2016 (UTC)

After passing the regex through bash, you get <nowiki>\\[[(].*\\[\])][^)\]]*$</nowiki> 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. [[Special:Contributions/108.162.216.44|108.162.216.44]] 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 ;-) --[[User:Kynde|Kynde]] ([[User talk: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.--[[Special:Contributions/162.158.90.208|162.158.90.208]] 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 https://en.wikipedia.org/wiki/Leaning_toothpick_syndrome.
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). [[User:Aasasd|Aasasd]] ([[User talk:Aasasd|talk]]) 10:13, 3 February 2016 (UTC)

:A funny comment about the MediaWiki software, which is even worse than this comic: <code><nowiki><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 :)</nowiki></code> ([https://phabricator.wikimedia.org/P110$275 source]) --[[Special:Contributions/162.158.91.215|162.158.91.215]] 10:18, 3 February 2016 (UTC)

Interestingly, I first looked at this on my phone (using <strike>Chrome</strike> 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. [[User:Jdluk|Jdluk]] ([[User talk:Jdluk|talk]]) 11:36, 3 February 2016 (UTC)

enough with the harry potter fancruft. "elder" is a [[Wiktionary:elder|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. --[[Special:Contributions/141.101.106.161|141.101.106.161]] 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."
: +1. Between the fact that harry potter (, ages, or tribes) aren't mentioned anywhere else in the text and the comic being a progressive list, I see this being the most likely explanation. Plus the metion of demons, which are easily the most* common usage of the modifier.
:: (*) or second most, after "elder gods", who are, let's face it, also demons. [[Special:Contributions/162.158.180.125|162.158.180.125]] 14:41, 3 February 2016 (UTC)
::: I'm pretty sure that "Elder backslash" is in reference to the "Elder gods" of Lovecraft. [[Special:Contributions/173.245.54.35|173.245.54.35]] 16:51, 3 February 2016 (UTC)
:::: Note also that it's called 'The Elder Wand' not as an intensifier, as in this comic and the other examples given, but because it is literally ''made from the wood of an [https://en.wikipedia.org/wiki/Sambucus_nigra Elder Tree]'' I'm pretty sure it's not an intentional reference. -Graptor [[Special:Contributions/173.245.54.23|173.245.54.23]] 19:29, 3 February 2016 (UTC)

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:

\[(AAAAA\[])]AAAAA

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?
[[User:Cmancone|Cmancone]] ([[User talk:Cmancone|talk]])cmancone

Ninjaed by Cmancone, above. I agree with that result in every respect except for the start-of-string being potentially anything, but putting my own analysis in here because it took long enough to type!
Depth-of-backslash might depend upon depth of utility. In Perl, <nowiki>''</nowiki>-quotes (among others) treat everything within as literal whilst ""-quotes (and variations) interpolates any special characters, variables, etc that you put in it. (Search for "Quote and Quote-like operators" in your favourite PerlDocs source.) '\sss' is a literal backslash followed by three 's' characters , while "\sss" is the special \s escape (a whitespace) followed by two further regular characters. You might need to define the first when you need to use it to provide a not-previously-escaped \s so that it might be escaped within another context. ''Or'' you define it as "\\sss" (escaped-\) the first time, as equivalent to '\sss'. But '\\sss' would be a literal that, later, could be interpreted as an escaped-\ to the input of a further context where the \s finally becomes 'match a whitespace'.

'\\\sss' would be literal, whilst "\\\sss" could be equivalent to '\ ss' (literal backslash, literal space, rest of characters). Then, instead of literal '\\sss', for some purpose, you could interpolate two escaped-backslashes "\\\\sss"... and so on.

Meanwhile I ''think'', just from visual inspection, "'''\\\[[(].*\\\[\])][^)\]]*$'''" in Bash should obey the interpolation rules quite nicely. The first two characters must be a literal backslash (from the escaped-backslash) and a literal open-square bracket (again, escaped). The next open-square and the close-square shortly after depict a character class that contains only an open-parenthesis, and could have been written as '''$'''.

The '''.*''' indicates zero-or-more (the asterix) instances of ''any'' character (the dot). There is then a literal backslash (from the next '''\\''' duo) and a literal open-square (the '''\[''' pair) and close-square (the '''\]''' pair). The ''')''' is literal and does not need escaping (as a parenthesis group had not yet been opened), as is the next ''']''' character. To be sure, I would have written these two as the pair escapes '''$\]''', but horses for courses...

Then there's another character class (the next '''[''' and the final ''']''') required zero-or-more times (the asterix) to use up all the rest of the characters to the end (the ending '''$''' character). As there was no '''^''' character (a.k.a. caret/circumflex/etc) at the start, the match isn't bothered about what unmatched characters appear before the original '''\('''. This character class, however, starts with a '''^''' which in this context (the very first character of a character-class definition, not somewhere where an entire match-string starts) indicates negation of the following selection, so it is all characters ''but'' those specified, which is the regular close-parenthesis and (because it needs to be contained within a '''[]''' pair) the escaped close-square.

So, all matching strings must start with '''\[(''', i.e. the backslash, open-square and open-paren. They can continue with ''any'' further text, before then having a '''\[])]''', i.e. backslash, open-and-close-squares and close-paren, close-square. After this, the match continues just as long as there are no non-closing square/classic brackets before the ending.

The minimum matching literal string would be '''\[(\[])]''' with longer variants being of the form '''X\[(Y\[])]Z''' where X and Y can be replaced by anything (or be absent), and Z can be replaced by anything (or absent!) ''so long as it doesn't contain possibly relevent close-brackets!''. The latter stipulation is likely because the Y (and X) ''is'' allowed to contain these characters, and for some reason you don't want to confuse the test by finding some other '''\[])]''' segment within the X/Y-zones. (In this context, it doesn't actually seem to matter too much. But it might do in ways I haven't spotted or just be a hang-over from a prior permutation of the test.)

The "grep -o" function is working on the output to the file being '''cat'''ed (there are alternate ways of doing this that some people might prefer), to only accept the lines in the file that match the '''X\[(Y\[])]Z''' string. These lines would appear to be lines of out.txt (a fairly generic name that reveals little to its original purpose) that are well-formed for some other purpose. A safety-escaped (i.e. not to be taken literally by any simple parser) '''[]'''-grouping containing a '''()'''-group (''not'' escaped, perhaps reasonably in context) containing potentially random text followed by an empty '''[]''' pair (again, safety-escaped). Depending on the source, the empty '''[]'''-pair could mean many things, as with the other layers. And the lines may end with any further text.

The "out.txt" file might be the result of a prior Grep (string-search function) quote possibly scanning code for lines of particular importance by another pattern and dumping the results to out.txt for further perusal. And then Randall finds the need to dig further into the first result by extracting just those already selected that all have the '''X\[(Y\[])Z]'''-ish pattern to them.

But I could be wrong, and that's way too long for an official explanation.
(Perhaps just something like the penultimate paragraph, if we're not entirely mistaken?) [[Special:Contributions/162.158.152.89|162.158.152.89]] 14:14, 3 February 2016 (UTC)

The regex is supposed to be looking for:
\\\ backslash
[[(] [ or (
.* any character (repeated 0 or more times)
space space
\\\ backslash
[[\])] probably meant to match either [, ] or ). However, it's not correct, it instead matches the literal characters [)]
[^)\]]* probably meant to match any character that isn't ) or ], repeated. Instead it means one character that's not a ), and then a ] zero or more times
$ end of string

The first problem is that you're not supposed to escape ] in a [...], and it also has to be first in the grouping (unless negated with a ^) It should be [][)] or something similar.
The second problem is the same. The last bit should be [^])]*$ and not [^)\]]*$. [[User:Khris|Khris]] ([[User talk:Khris|talk]]) 14:24, 3 February 2016 (UTC)

I was reading through the regex, if using grep you run into an error with an unmatched ")". Removing this gets a string such as \[(AAAAA\[]]AAAAA$ http://regexr.com/3cng8 [[Special:Contributions/162.158.214.230|162.158.214.230]] 14:42, 3 February 2016 (UTC)

The regex relies on several special cases (*surprise*).
First: bash double-quote expansion (see [https://www.gnu.org/software/bash/manual/html_node/Double-Quotes.html#Double-Quotes]). Perhaps non-intuitively, \\\ followed by a character that \ doesn't escape is an escaped backslash followed by a literal backslash, effectively the same as \\\\ followed by that same non-escaped character. After bash double-quote expansion, this results in:

\\[[(].*\\[\])][^)\]]*$

grep interprets this as:

# any leading non-\ characters
# literal backslash
# character class containing [ and (
# zero or more *any* characters
# another literal backslash
# yet another literal backslash, via a character class containing only a backslash. Note this does not contain an escaped ], as it might appear at first glance. See [http://www.gnu.org/software/grep/manual/html_node/Character-Classes-and-Bracket-Expressions.html]
# literal )
# literal ]
# character class of anything except ), \
# zero or more ]
# end of line

Matching examples:
*echo 'asdf\[asdfasdf\\)]a]]]]]]' | grep -o "\\\[[(].*\\\[\])][^)\]]*$"
*echo '$\$]P' | grep -o "\\\[[(].*\\\[\])][^)\]]*$"

One key thing to understand is that \ is not a special character when it's in a bracket expression - you can't escape characters in bracket expressions. So [^)\] simply means any character other then ) or \. Also, ( and ) are just regular characters unless they are escaped in basic regular expressions - extended regular expressions reverse this rule.
----
[[Special:Contributions/108.162.216.34|108.162.216.34]] 16:14, 3 February 2016 (UTC)rb

I don't know about the regular expression in the title text, but I think the explanation is incorrect in that it starts off talking about regular expressions. Escaping backslashes is an issue with strings in programming in general. [[Special:Contributions/173.245.54.46|173.245.54.46]] 17:12, 3 February 2016 (UTC)
----
I suspect that Randall may have used the regexp in the title text to *find* malformed regular expressions in a file (out.txt) that he (or someone) had previously filled with output from some error message (or collection of error messages, or at least the output of something where a regular expression had been expected to work but had not worked as expected). [[Special:Contributions/162.158.252.227|162.158.252.227]] 19:06, 3 February 2016 (UTC)

You can use metacharacters in character classes, the only metacharacters in a character class that must be escaped are the closing square bracket (]), the backslash (\), the hyphen, and the carat and hyphen (^) if they are the first listed item in the set. The closing square bracket requires escaping because including it without would signal the end of the set otherwise, which then means the backslash must also be escaped. The hyphen must be escaped because, without it, it signals a range (unless it is listed first, then it is literal without escaping). Carat when listed first because otherwise it signals a negative set. 
Therefore, the end of the title text regex matches a backslash followed by either ] or ), which is then followed by any number (including none) of characters so long as they are not ] nor ) which means the whole regex can match "\[something\] more" or "$something$more" or "\[something\) more" as well as "\[something\]". — [[Special:Contributions/162.158.255.117|162.158.255.117]] 01:16, 4 February 2016 (UTC)

I'll add that I use an ''almost identical'' regex in my mail server for matching mailing-list subject lines which often have a format of "[Listname] normal subject line" which made it pretty recognizable to me. — [[Special:Contributions/162.158.255.117|162.158.255.117]] 01:24, 4 February 2016 (UTC)

== Example of a match ==

First, the shell will do some escaping substitution. So, in order to easily read it, let's see what grep really receives:

$ echo "\\\[[(].*\\\[\])][^)\]]*$"
\\[[(].*\\[\])][^)\]]*$

Let's break it out:

* <code>\\</code> matches a <code>\</code>
* <code>[[(]</code> matches either a <code>[</code> or a <code>(</code>
* <code>.*</code> matches any series of characters until the next match
* <code>\\</code> matches a <code>\</code>
* <code>[\]</code> matches a <code>\</code>
* <code>)]</code> matches <code>)]</code>
* <code>[^)\]</code> matches anything but <code>)</code> or <code>\</code>
* <code>]*</code> matches any number of <code>]</code> (including none)
* <code>$</code> matches the end of the string

So the string '''\[aaa\]\\)]a]]]]]]''' matches!

Talk:1638: Backslashes

2016-02-04T01:16:32Z

162.158.255.117: character set escaping required for some metacharacters

...Maybe it's meant to search for all Game Grumps transcripts which make mention of the "[http://gamegrumps.wikia.com/wiki/Grep Grep]" gag? [[Special:Contributions/108.162.216.55|108.162.216.55]] 15:53, 3 February 2016 (UTC)

It should be noted that this also occurs in almost every programming language where "\" is the escape character. i.e.
print("Hello")
> Hello
print("\"Hello\"")
> "Hello"
print("\\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 [http://www.explainxkcd.com/wiki/index.php/1246:_Pale_Blue_Dot 1246] (title text) and [http://www.explainxkcd.com/wiki/index.php/1419:_On_the_Phone 1419].)
[[Special:Contributions/173.245.54.29|173.245.54.29]] 06:14, 3 February 2016 (UTC)
:[[:Category:Ba'al|Did that]] before seeing you comment, so yes I agree. --[[User:Kynde|Kynde]] ([[User talk:Kynde|talk]]) 09:47, 3 February 2016 (UTC)

The last entry may also be an oblique reference to the infinitely-expandable recursive acronym "GOD = GOD Over Djinn" mentioned in Richard Hofstadter's Gödel, Escher, Bach.[[User:Taibhse|Taibhse]] ([[User talk:Taibhse|talk]]) 16:42, 3 February 2016 (UTC)

;I don't think the regex is invalid

According to <tt>man grep</tt> you need to specify the <tt>-E</tt> 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?). {{unsigned ip|141.101.66.83}}

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 [[Special:Contributions/197.234.242.243|197.234.242.243]] 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. --[[Special:Contributions/198.41.238.231|198.41.238.231]] 07:47, 3 February 2016 (UTC)
:I agree. But I cannot help either.--[[User:Kynde|Kynde]] ([[User talk:Kynde|talk]]) 09:51, 3 February 2016 (UTC)

This is the third time Randall has mentioned Ba'al the Soul Eater xD [[User:International Space Station|International Space Station]] ([[User talk: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. --[[User:Kynde|Kynde]] ([[User talk:Kynde|talk]]) 09:51, 3 February 2016 (UTC)

After passing the regex through bash, you get <nowiki>\\[[(].*\\[\])][^)\]]*$</nowiki> 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. [[Special:Contributions/108.162.216.44|108.162.216.44]] 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 ;-) --[[User:Kynde|Kynde]] ([[User talk: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.--[[Special:Contributions/162.158.90.208|162.158.90.208]] 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 https://en.wikipedia.org/wiki/Leaning_toothpick_syndrome.
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). [[User:Aasasd|Aasasd]] ([[User talk:Aasasd|talk]]) 10:13, 3 February 2016 (UTC)

:A funny comment about the MediaWiki software, which is even worse than this comic: <code><nowiki><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 :)</nowiki></code> ([https://phabricator.wikimedia.org/P110$275 source]) --[[Special:Contributions/162.158.91.215|162.158.91.215]] 10:18, 3 February 2016 (UTC)

Interestingly, I first looked at this on my phone (using <strike>Chrome</strike> 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. [[User:Jdluk|Jdluk]] ([[User talk:Jdluk|talk]]) 11:36, 3 February 2016 (UTC)

enough with the harry potter fancruft. "elder" is a [[Wiktionary:elder|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. --[[Special:Contributions/141.101.106.161|141.101.106.161]] 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."
: +1. Between the fact that harry potter (, ages, or tribes) aren't mentioned anywhere else in the text and the comic being a progressive list, I see this being the most likely explanation. Plus the metion of demons, which are easily the most* common usage of the modifier.
:: (*) or second most, after "elder gods", who are, let's face it, also demons. [[Special:Contributions/162.158.180.125|162.158.180.125]] 14:41, 3 February 2016 (UTC)
::: I'm pretty sure that "Elder backslash" is in reference to the "Elder gods" of Lovecraft. [[Special:Contributions/173.245.54.35|173.245.54.35]] 16:51, 3 February 2016 (UTC)
:::: Note also that it's called 'The Elder Wand' not as an intensifier, as in this comic and the other examples given, but because it is literally ''made from the wood of an [https://en.wikipedia.org/wiki/Sambucus_nigra Elder Tree]'' I'm pretty sure it's not an intentional reference. -Graptor [[Special:Contributions/173.245.54.23|173.245.54.23]] 19:29, 3 February 2016 (UTC)

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:

\[(AAAAA\[])]AAAAA

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?
[[User:Cmancone|Cmancone]] ([[User talk:Cmancone|talk]])cmancone

Ninjaed by Cmancone, above. I agree with that result in every respect except for the start-of-string being potentially anything, but putting my own analysis in here because it took long enough to type!
Depth-of-backslash might depend upon depth of utility. In Perl, <nowiki>''</nowiki>-quotes (among others) treat everything within as literal whilst ""-quotes (and variations) interpolates any special characters, variables, etc that you put in it. (Search for "Quote and Quote-like operators" in your favourite PerlDocs source.) '\sss' is a literal backslash followed by three 's' characters , while "\sss" is the special \s escape (a whitespace) followed by two further regular characters. You might need to define the first when you need to use it to provide a not-previously-escaped \s so that it might be escaped within another context. ''Or'' you define it as "\\sss" (escaped-\) the first time, as equivalent to '\sss'. But '\\sss' would be a literal that, later, could be interpreted as an escaped-\ to the input of a further context where the \s finally becomes 'match a whitespace'.

'\\\sss' would be literal, whilst "\\\sss" could be equivalent to '\ ss' (literal backslash, literal space, rest of characters). Then, instead of literal '\\sss', for some purpose, you could interpolate two escaped-backslashes "\\\\sss"... and so on.

Meanwhile I ''think'', just from visual inspection, "'''\\\[[(].*\\\[\])][^)\]]*$'''" in Bash should obey the interpolation rules quite nicely. The first two characters must be a literal backslash (from the escaped-backslash) and a literal open-square bracket (again, escaped). The next open-square and the close-square shortly after depict a character class that contains only an open-parenthesis, and could have been written as '''$'''.

The '''.*''' indicates zero-or-more (the asterix) instances of ''any'' character (the dot). There is then a literal backslash (from the next '''\\''' duo) and a literal open-square (the '''\[''' pair) and close-square (the '''\]''' pair). The ''')''' is literal and does not need escaping (as a parenthesis group had not yet been opened), as is the next ''']''' character. To be sure, I would have written these two as the pair escapes '''$\]''', but horses for courses...

Then there's another character class (the next '''[''' and the final ''']''') required zero-or-more times (the asterix) to use up all the rest of the characters to the end (the ending '''$''' character). As there was no '''^''' character (a.k.a. caret/circumflex/etc) at the start, the match isn't bothered about what unmatched characters appear before the original '''\('''. This character class, however, starts with a '''^''' which in this context (the very first character of a character-class definition, not somewhere where an entire match-string starts) indicates negation of the following selection, so it is all characters ''but'' those specified, which is the regular close-parenthesis and (because it needs to be contained within a '''[]''' pair) the escaped close-square.

So, all matching strings must start with '''\[(''', i.e. the backslash, open-square and open-paren. They can continue with ''any'' further text, before then having a '''\[])]''', i.e. backslash, open-and-close-squares and close-paren, close-square. After this, the match continues just as long as there are no non-closing square/classic brackets before the ending.

The minimum matching literal string would be '''\[(\[])]''' with longer variants being of the form '''X\[(Y\[])]Z''' where X and Y can be replaced by anything (or be absent), and Z can be replaced by anything (or absent!) ''so long as it doesn't contain possibly relevent close-brackets!''. The latter stipulation is likely because the Y (and X) ''is'' allowed to contain these characters, and for some reason you don't want to confuse the test by finding some other '''\[])]''' segment within the X/Y-zones. (In this context, it doesn't actually seem to matter too much. But it might do in ways I haven't spotted or just be a hang-over from a prior permutation of the test.)

The "grep -o" function is working on the output to the file being '''cat'''ed (there are alternate ways of doing this that some people might prefer), to only accept the lines in the file that match the '''X\[(Y\[])]Z''' string. These lines would appear to be lines of out.txt (a fairly generic name that reveals little to its original purpose) that are well-formed for some other purpose. A safety-escaped (i.e. not to be taken literally by any simple parser) '''[]'''-grouping containing a '''()'''-group (''not'' escaped, perhaps reasonably in context) containing potentially random text followed by an empty '''[]''' pair (again, safety-escaped). Depending on the source, the empty '''[]'''-pair could mean many things, as with the other layers. And the lines may end with any further text.

The "out.txt" file might be the result of a prior Grep (string-search function) quote possibly scanning code for lines of particular importance by another pattern and dumping the results to out.txt for further perusal. And then Randall finds the need to dig further into the first result by extracting just those already selected that all have the '''X\[(Y\[])Z]'''-ish pattern to them.

But I could be wrong, and that's way too long for an official explanation.
(Perhaps just something like the penultimate paragraph, if we're not entirely mistaken?) [[Special:Contributions/162.158.152.89|162.158.152.89]] 14:14, 3 February 2016 (UTC)

The regex is supposed to be looking for:
\\\ backslash
[[(] [ or (
.* any character (repeated 0 or more times)
space space
\\\ backslash
[[\])] probably meant to match either [, ] or ). However, it's not correct, it instead matches the literal characters [)]
[^)\]]* probably meant to match any character that isn't ) or ], repeated. Instead it means one character that's not a ), and then a ] zero or more times
$ end of string

The first problem is that you're not supposed to escape ] in a [...], and it also has to be first in the grouping (unless negated with a ^) It should be [][)] or something similar.
The second problem is the same. The last bit should be [^])]*$ and not [^)\]]*$. [[User:Khris|Khris]] ([[User talk:Khris|talk]]) 14:24, 3 February 2016 (UTC)

I was reading through the regex, if using grep you run into an error with an unmatched ")". Removing this gets a string such as \[(AAAAA\[]]AAAAA$ http://regexr.com/3cng8 [[Special:Contributions/162.158.214.230|162.158.214.230]] 14:42, 3 February 2016 (UTC)

The regex relies on several special cases (*surprise*).
First: bash double-quote expansion (see [https://www.gnu.org/software/bash/manual/html_node/Double-Quotes.html#Double-Quotes]). Perhaps non-intuitively, \\\ followed by a character that \ doesn't escape is an escaped backslash followed by a literal backslash, effectively the same as \\\\ followed by that same non-escaped character. After bash double-quote expansion, this results in:

\\[[(].*\\[\])][^)\]]*$

grep interprets this as:

# any leading non-\ characters
# literal backslash
# character class containing [ and (
# zero or more *any* characters
# another literal backslash
# yet another literal backslash, via a character class containing only a backslash. Note this does not contain an escaped ], as it might appear at first glance. See [http://www.gnu.org/software/grep/manual/html_node/Character-Classes-and-Bracket-Expressions.html]
# literal )
# literal ]
# character class of anything except ), \
# zero or more ]
# end of line

Matching examples:
*echo 'asdf\[asdfasdf\\)]a]]]]]]' | grep -o "\\\[[(].*\\\[\])][^)\]]*$"
*echo '$\$]P' | grep -o "\\\[[(].*\\\[\])][^)\]]*$"

One key thing to understand is that \ is not a special character when it's in a bracket expression - you can't escape characters in bracket expressions. So [^)\] simply means any character other then ) or \. Also, ( and ) are just regular characters unless they are escaped in basic regular expressions - extended regular expressions reverse this rule.
----
[[Special:Contributions/108.162.216.34|108.162.216.34]] 16:14, 3 February 2016 (UTC)rb

I don't know about the regular expression in the title text, but I think the explanation is incorrect in that it starts off talking about regular expressions. Escaping backslashes is an issue with strings in programming in general. [[Special:Contributions/173.245.54.46|173.245.54.46]] 17:12, 3 February 2016 (UTC)
----
I suspect that Randall may have used the regexp in the title text to *find* malformed regular expressions in a file (out.txt) that he (or someone) had previously filled with output from some error message (or collection of error messages, or at least the output of something where a regular expression had been expected to work but had not worked as expected). [[Special:Contributions/162.158.252.227|162.158.252.227]] 19:06, 3 February 2016 (UTC)

You can use metacharacters in character classes, the only metacharacters in a character class that must be escaped are the closing square bracket (]), the backslash (\), the hyphen, and the carat and hyphen (^) if they are the first listed item in the set. The closing square bracket requires escaping because including it without would signal the end of the set otherwise, which then means the backslash must also be escaped. The hyphen must be escaped because, without it, it signals a range (unless it is listed first, then it is literal without escaping). Carat when listed first because otherwise it signals a negative set. 
Therefore, the end of the title text regex matches a backslash followed by either ] or ), which is then followed by any number (including none) of characters so long as they are not ] nor ) which means the whole regex can match "\[something\] more" or "$something$more" or "\[something\) more" as well as "\[something\]". — [[Special:Contributions/162.158.255.117|162.158.255.117]] 01:16, 4 February 2016 (UTC)

== Example of a match ==

First, the shell will do some escaping substitution. So, in order to easily read it, let's see what grep really receives:

$ echo "\\\[[(].*\\\[\])][^)\]]*$"
\\[[(].*\\[\])][^)\]]*$

Let's break it out:

* <code>\\</code> matches a <code>\</code>
* <code>[[(]</code> matches either a <code>[</code> or a <code>(</code>
* <code>.*</code> matches any series of characters until the next match
* <code>\\</code> matches a <code>\</code>
* <code>[\]</code> matches a <code>\</code>
* <code>)]</code> matches <code>)]</code>
* <code>[^)\]</code> matches anything but <code>)</code> or <code>\</code>
* <code>]*</code> matches any number of <code>]</code> (including none)
* <code>$</code> matches the end of the string

So the string '''\[aaa\]\\)]a]]]]]]''' matches!