Filename with dot in front
What does the dot mean
The question is pretty straight forward. I can get the exit code of the previous command by using $?. But what exactly is it?  I don't think it is a variable, because you can't have any special characters in the name of variable other than _.  foo?foo=10   will result in the error: foo?foo=10: command not found  So if it is not a variable, what is it? Are there others like it? Is the Higgs boson an elementary particle? If so, why does it decay? The  is an excitation of the Higgs field and is very massive and short lived. It also interacts with the Higgs field and thus is able to experience mass.   Why does it decay if it is supposed to be an elementary particle according to the standard model? Failed upgrade from Ubuntu 19.10 to 20.04 "Please update the microcode" While installing the Ubuntu 20.04 updates during upgrade from 19.10 to 20.04, my screen suddenly went completely white and displayed a message saying  Please logout and try again.  But I could not locate my cursor and so I switched off my laptop. After restarting it again, it was showing an error message saying  Please update the microcode  Why did this happen? How can I solve this problem? Where were the cannons in final fight in Wakanda in Infinity War? In Black Panther, Ulysses Klaue describes his arm cannon as a leaf blower in comparison to the cannons/weapons that Wakanda has.  Infinity War comes after the events of Black Panther, so the weapons should exist. During the final fight with the children of Thanos and Space Dogs (as Rocket refers to them), Wakandans could have used these powerful cannons, pointing them at the opened section of barrier. Instead they chose a fist fight.  Even M'Baku says that it would be the end of Wakanda, so the magnitude is huge and risks are very high. Why were these powerful weapons not used?    Edit 1: I watched the movie again and planes are there in the fight. But they were only used to destroy the spaceships that crashed. What happens if both players have the ability to pump their creature an unlimited number of times? Say that both players each had 2 , 2 , and a . (Or any other way to get unlimited mana, and a Nantuko Shade).  Player 1 attacks with his , and player 2 blocks with his . Before damage is assigned, each has chances to pump up their  as much as they want. They can't just declare them to be "infinite," but each can always one-up the other player. What happens?  It seems there would be a loop of events, but would one player eventually be forced to break the loop as per rule 714.3? Is it considered the same game state after each player pumps their creature a bunch as it was before?  This was discussed at length on the Draw3Cards Magic Q&amp;A site (which is no longer available), but no conclusion was reached. Some felt that the game would simply be a draw, others felt that the active player would be forced to make a different decision to break the loop. Others felt that you would just have to call a judge and see what he decides. An example of a sequence of Riemann integrable functions $(f_n)$ that converges pointwise to a function $f$ that is not Riemann integrable. Set of continuity points of a real function I have a question about subsets $$ A \subseteq \mathbb R $$ for which there exists a function $$f : \mathbb R \to \mathbb R$$ such that the set of continuity points of $f$ is $A$. Can I characterize this kind of sets? In a topological,measurable or in some way? For example, does there exist a function continuous on $\mathbb Q$ and discontinuous on the irrationals? I have problems with my Tilgin Vood Router. As I try to start my router by turning the power on (captain obvious), it generally doesn't work the first 3-4 times. This is getting very annoying.  Five minutes after turning the power on the router's signal LEDs don't blink in the way they should do in a connected state. I can connect to my routers web configuration interface through my PC connected to it via LAN though I can't access the internet.  It usually takes the router five minutes to get to the point where it should be connected to the internet but as it doesn't work the first times.  So I turn on my router 3-5 times, let him work 5 minutes and then suddenly, after turning the power off and on again it all works.  I also have to restart my PC too in order for everything to work.   How can I solve this problem? Just leave the router turned on all time? I prefer a daily IP switch, though. May the problem have something to do with my PC? There is another one connected to the router too and it doesn't work there either. I want to know all sets of single-variate functions that fulfill the following qualities: $\forall_{f:R^2 \to R^2} \forall_{g \in CAF} \forall_{h \in CAF} \exists_{k\in CAF} k(x) = f(g(x),h(x))$ where CAF is the set I am wishing to find. I know that the set of constants and the set of piece wise constants each satisfy that equation. Do any others? How do I prove that $x^p-x+a$ is irreducible in a field with $p$ elements when $a\neq 0$? Solder does not stick to tip of soldering iron? Basic question here, but it's driving me insane!  The solder does not seem to stick to the tip of my soldering iron. After the iron heats up, the tip appears black (sometimes on all sides and sometimes on one side), then either it doesn't melt the solder at all, or it I fiddle around with it for a while; it melts the solder, but the solder rolls into itself into a ball and doesn't stick to the tip.  I've seen this many times while soldering before and usually it's solved by cleaning the tip on a soldering sponge or cooling it down and scraping the tip off with a blade, but I have scraped this particular one many times and still it's the same problem: it heats up and gets black, then the solder doesn't stick to it.  It doesn't help that this soldering iron has a very fine tip and I have to use it to solder very tiny chips and wires under a microscope (I'm just starting to learn soldering under microscopes).  Any ideas on what I can do?    PS: Is scraping the tip a bad idea? I have been doing it with my other bigger soldering irons and it seemed to work (at least in most cases) but I am not sure whether it is a good solution or not. how to calculate $$\int_0^\infty \frac{x^{3}}{e^{x}-1} \; dx$$   Be $q:= e^{z}-1 , p:= z^{3}$ , then $e^{z} = 1 $ if $z= 2\pi n i $, so the residue at 0 is : $$\frac{p(z_{0})}{q&#39;(z_{0})} = 2\pi i n ^{3}$$  problem is that this is not symmetric, so how does one find the definite integral? If $\cot A+\cot B+\cot C=\sqrt3$ then prove that the triangle is equilateral triangle.   Trial: I can counter check that this is true as $\cot 60+\cot 60+\cot 60=3 \frac{1}{\sqrt3}=\sqrt3$.Here I also know that $A+B+C=180$. But I am unable to show it. Please help. How should we handle downvote retaliation? I have a situation where I'm trying to figure out what the right thing to do is on SO.    I see a question.  I answer the question.  I see there are a couple other answers.  One answers the question well, though with less explanation than my answer.  The other answer seems both wrong and irrelevant to the question (doesn't answer the question at all).  I comment to that effect.  The "wrong" part is edited out, but the author of the answer doesn't respond to how their answer actually answers the question.  In fact, they seem offended that I don't "get" it.  After giving them several chances to explain how their answer is relevant to the question and seeing their attitude, I decide to downvote their answer as I don't see how it addresses the question at all and the author won't explain.  They retaliate and downvote my answer and admit in their comments that their downvote of my answer has nothing to do with the content of my answer and only because they don't like me disputing their answer.  Did I do the right thing by downvoting their answer?  Do I just have to live with their downvote retaliation?  Anything I should have done differently?  I also have no way of knowing this for sure, but the next question I answered was upvoted, then downvoted so perhaps this same person is stalking my answers and downvoting other answers of mine too with no comment.  As long as this doesn't continue, I'm not losing sleep over a couple downvotes, but I do wonder if I should have done anything differently.  Followup Later After I Posted This Question: After thinking about it for a little while, the person who disagreed with me decided to delete their post.  So, eventually the message did get through to them.  I don't know if they rescinded their downvote or not (or if they even could). Trigger Task Scheduler in Windows 7 when computer wakes up from sleep/hibernate I don't want task scheduler or whatever to wake the computer, but when I open the laptop back up and the machine wakes I'd like that to be the trigger that task scheduler or something uses to run an app. When to use an interface instead of an abstract class and vice versa? How to publish a post with empty title and empty content? Why I'm doing this you might ask? I'm developing a website for a business with a portfolio where the gallery items are posts. These posts are populated through custom fields and category selections, nothing else.  For each item, there could be a title/content or not, it depends on the item in question and that's entirely up to the client. They are the ones populating their portfolio and not me. I'm just building the system for them to easily publish whatever they want.  I realize that WordPress might have some issues with posts without a title, that's why I implemented (in functions.php) a function to auto set a title for the post if none was attributed. This post auto title will never be shown on the website cause I look for it and omit it if it's there, otherwise, show the attributed title to the post.  The function for that is:  add_action('publish_post', 'insert_automatic_post_title', 10, 2);  function insert_automatic_post_title($postID, $post) {     if($post-&gt;post_title === '') {         $post-&gt;post_title = '['.get_the_date('d/m/Y @ H:i:s').']';          if($post-&gt;post_name == $postID) {             $post-&gt;post_name = sanitize_title($post-&gt;post_title);         }          $result = wp_update_post($post);     } }   The only problem is that if title is empty and the content is also empty (with some custom fields already defined) that function above will never be called and the post won't be published, it will remain in draft status.  The only solution I could think of was to create some shortcode like [empty_post] and ask the client to set that on the post content when he does not wish to attribute a title/content to the post. That shortcode could print something like &lt;!-- EMPTY POST --&gt; or even nothing at all. The fact that there's something in the post content, the function above is called, an automatic title is set and the post is published.  But I'm looking for a way where the client doesn't need to have more trouble (i.e: inserting a shortcode into the post content) than what's needed, I want it to be as simple as possible. Without messing with WordPress source code of course.  Can anyone think of another way with actions/filters? Help us test the alpha version of our Android app We are in the early stages of development of the official Stack Exchange Android app and we need your help with testing. To set a few expectations: there will be bugs, crashes, and missing features, all of which will be fixed in .    We are initially targeting Android devices running  (Android 4.1 or higher) starting with phones (up to ~5 inch) and eventually moving our way to tablets.    To register for alpha testing .  After you register we will send you an invite to a private Google community where you can find a link to download our app directly from the  store. The invitations will be sent out in waves, so if you don’t get an invite immediately, be patient.  Crash reports will be automatically reported back to us using . Bugs or feature requests should be reported here on meta and tagged . Please do not use the Google community to report bugs.  As always, we welcome your feedback and are committed to building the best mobile app possible for browsing the Stack Exchange sites. I read that it is a best practice to double quote all of your variable expansions in Bash. I also read that one cannot use a shell glob (wildcard(*)) right after a double quoted variable expansion. These situations conflict when one wants use the value of a regex pattern, expanded out of a variable.   The reason I would sometimes want to combine regex with a wildcard is to keep my regex minimal, neater, in my personal taste.  My particular problem  I downloaded phpmyadmin into my document root directory and unzipped it, but I fail to rename it with mv by a regex pattern I put in a variable, and available when expanding its variable. Here's the exact trace:  userName@compName:/var/www/html# ll total 11336 drwxr-xr-x  3 root root     4096 Feb 14 07:04 ./ drwxr-xr-x  3 root root     4096 Feb 14 06:56 ../ -rw-r--r--  1 root root      612 Feb 14 06:57 index.nginx-debian.html drwxr-xr-x 12 root root     4096 Dec 23 08:50 phpMyAdmin-4.7.7-all-languages/ -rw-r--r--  1 root root 11589684 Dec 23 14:08 phpMyAdmin-latest-all-languages.zip userName@compName:/var/www/html# echo $pma [pP][hH][pP][mM][yY][aA][dD][mM][iI][nN] userName@compName:/var/www/html# mv "$pma"*/ phpmyadmin/ mv: cannot stat '[pP][hH][pP][mM][yY][aA][dD][mM][iI][nN]*/': No such file or directory   If I'll unquote the variable expansion to ${pma} I would indeed be able to combine the variable expansion and the regex, as in ${pma}*, but it is important to me to follow the best practice without exceptions, if I can.  My question  How could I keep the variable expansion double quoted, but still using the extracted value with a wildcard? OL3 How to select features of a WMS layer