I have tried fiddling with echo command to to add $_GET to a text file but looks like it does not work but escaping it with \ works may be because $ is special character in bash.   For example, echo "\$_GET" &gt;&gt; newfile.txt works.    What I wanted to ask is how does echo work in each of the following two cases in the given screenshot. The second functionality of echo is what I am not able to grasp.
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?
If $\gcd (a,b) = 1$, what can be said about $\gcd (a+b,a-b)$? Suppose $a, b \in \mathbb{Z}$, $a &gt; b$, and $\gcd (a,b) = 1$.  What can be said about $\gcd (a+b,a-b)$?  Is it true in general that $\gcd (a+b,a-b) \leq 2$? Can there be two distinct, continuous functions that are equal at all rationals? Akhil showed that the  is the same as the continuum, using as a step the observation that continuous functions that agree at rational points must agree everywhere, since the rationals are dense in the reals.  This isn't an obvious step, so why is it true? Git ignore file for Xcode projects How to "unpivot" or "reverse pivot" in Excel? I have data that looks like this:  Id | Loc1 | Loc2 | Loc3 | Loc4 ---+------+------+------+----- 1  | NY   | CA   | TX   | IL 2  | WA   | OR   | NH   | RI   And I want to convert it to this:  Id | LocNum | Loc ---+--------+---- 1  |   1    | NY 1  |   2    | CA 1  |   3    | TX 1  |   4    | IL 2  |   1    | WA 2  |   2    | OR 2  |   3    | NH 2  |   4    | RI   What's the easiest way to do this in Excel 2007? Deleted comments leave badge on iOS app When someone leaves a comment that involves you being notified, you get the notification both on the main toolbar on Stack Exchange and as a notification/badge on the iOS app.  If you read a comment on the website and cause the notification to be removed from the toolbar, the badge also gets removed from the iOS app.  However, when a comment that has previously caused a notification/badge to appear on iOS gets deleted, the badge remains on the iOS app while the notification gets removed from the website toolbar.  Could the badge also be removed from the iOS app in this situation? Problem: Let $X$ and $Y$ be independent and suppose that each has a $\text{Uniform}(0,1)$ distribution. Let $Z = \min\{X, Y\}$. Find the density $f_Z(z)$ for $Z$. Hint: It might be easier to first find $\mathbb{P}(Z &gt; z)$.  Attempted Solution:  Given that $X, Y \sim \text{Uniform}(0,1)$, how do we not just have the following?  $$ f_Z(t) = f_X(t) = f_Y(t) = \begin{cases} 1 &amp; \text{if } 0 \le t \le 1 \\                                           0 &amp; \text{otherwise}                             \end{cases} $$  Of course I'm highly suspicious of this answer because it's not making use of the fact that $X$ and $Y$ are independent, nor is it making use of the provided hint. Analysing Bounce Rate and Time on Page I'm working on an eCommerce site and there's a perceived problem with the bounce rates on product pages. The best performing page (in terms of views), tends to have a very high bounce rate, at about 80%. This page is also targeted with Ads, but in both non-paid and paid traffic, the bounce rate stays high.  What's weird about it is that the time on this page is about 2 and a half minutes. The others pages have a slightly lower bounce rate (between 50% and 75%) with visit times between 1 minute and 2 minutes.  I'm not entirely sure about how to analyse this data. I've checked all the possible technical problems (faulty GA code, JS race conditions, breaks in the chain), and whilst there were some things that need improving, no technical fix budged the bounce rate at all.  The other thing we noticed was that the product pages were getting lots of traffic for very generic and brand based search terms. In these cases the pages come up as sitelinks, could this explain a high bounce rate too?  So in short :  If the page view time is so high, should I be worrying about the bounce rate at all? What's the chances of someone visiting the page and then leaving to compare prices? And how do sitelinks affect bounce rate on eCommerce sites? The standard font packages make global changes to the fonts in my document. What if I want to use a particular font for just a portion of my text?   How do I find the right name of the font? How do I select the font? How do I restrict the scope of the font change?     There are separate answers for different flavors of TeX (quick links): How to determine callee function name in a script To make it short, doing something like:  -bash$ function tt {  echo $0; }  -bash$ tt   $0 will return -bash, but how to get the function name called, i.e. tt in this example instead? Is $\frac{\textrm{d}y}{\textrm{d}x}$ not a ratio? In the book Thomas's Calculus (11th edition) it is mentioned (Section 3.8 pg 225) that the derivative $dy/dx$ is not a ratio. Couldn't it be interpreted as a ratio, because according to the formula $dy = f'(x)dx$ we are able to plug in values for $dx$ and calculate a $dy$ (differential). Then if we rearrange we get $dy/dx$ which could be seen as a ratio.   I wonder if the author says this because $dx$ is an independent variable, and $dy$ is a dependent variable, for $dy/dx$ to be a ratio both variables need to be independent.. maybe? What is the maximum or minimum tire width I can fit on my bicycle How can I use Photoshop to imitate a photo taken with a low-quality camera? How can I create an image in Photoshop that imitates a photo taken with a low-quality phone camera? Examples of qualities I want to simulate:   blurring in some areas caused by a dirty lens low quality exposure handling in the darkroom noise   Some examples: Example of a series! Give an example of a convergent series $$\sum_{n=1}^{\infty}a_n$$ such that the series $$\sum_{n=1}^{\infty}a_{3n}$$ is divergent..  I cannot find find any kind of series... I am also be very thankful if you find a divergent series (changing the term convergent)... How to downgrade a package via apt-get? Currently using ubuntu 15.10 on azure and installed the gnome and vnc4server latest version on ubuntu. Please find log file below:  Current VNC client screen:    $ cat .vnc/myhost1\:1.log    --cut-- VNCSConnST:  Server default pixel format depth 16 (16bpp) little-endian rgb565 VNCSConnST:  Client pixel format depth 8 (8bpp) colour-map Window manager warning: Invalid WM_TRANSIENT_FOR window 0x20000c specified for    0x20000b (I        nitialization error). Error org.freedesktop.DBus.Error.NameHasNoOwner: Could not get owner of name    'org.gnome.ze        itgeist.Engine': no such name amdxdg-su: no graphical method available for invoking '/usr/bin/amdcccle' as 'root'  $ cat .vnc/xstartup unset SESSION_MANAGER  [ -x /etc/vnc/xstartup ] &amp;&amp; exec /etc/vnc/xstartup [ -r $HOME/.Xresources ] &amp;&amp; xrdb $HOME/.Xresources  vncconfig -iconic &amp;  gnome-panel &amp; gnome-settings-daemon &amp; metacity &amp; nautilus -n &amp; gnome-terminal &amp;   How to get 24bit color with wide screen (Now I getting square screen in vnc client) How to parse a time into a Date object from user input in JavaScript? I am working on a form widget for users to enter a time of day into a text input (for a calendar application). Using JavaScript (we are using jQuery FWIW), I want to find the best way to parse the text that the user enters into a JavaScript Date() object so I can easily perform comparisons and other things on it.  I tried the parse() method and it is a little too picky for my needs. I would expect it to be able to successfully parse the following example input times (in addition to other logically similar time formats) as the same Date() object:   1:00 pm 1:00 p.m. 1:00 p 1:00pm 1:00p.m. 1:00p 1 pm 1 p.m. 1 p 1pm 1p.m. 1p 13:00 13   I am thinking that I might use regular expressions to split up the input and extract the information I want to use to create my Date() object. What is the best way to do this? Why do we need the trilogy instead of just one site? I have seen many examples of how to render sprites from a spritesheet but I havent grasped why it is the most common way of dealing with sprites in 2d games.  I have started out with 2d sprite rendering in the few demo applications I've made by dealing with each animation frame for any given sprite type as its own texture - and this collection of textures is stored in a dictionary. This seems to work for me, and suits my workflow pretty well, as I tend to make my animations as gif/mng files and then extract the frames to individual pngs.  Is there a noticeable performance advantage to rendering from a single sheet rather than from individual textures? With modern hardware that is capable of drawing millions of polygons to the screen a hundred times a second, does it even matter for my 2d games which just deal with a few dozen 50x100px rectangles?  The implementation details of loading a texture into graphics memory and displaying it in XNA seems pretty abstracted. All I know is that textures are bound to the graphics device when they are loaded, then during the game loop, the textures get rendered in batches. So it's not clear to me whether my choice affects performance.  I suspect that there are some very good reasons most 2d game developers seem to be using them, I just don't understand why. Find the Unit Vector of a Three Dimensional Vector Jawa asked me this  and I didn't know the answer. So I present it to the meta SO community:     [To get the Yearling badge] Do you need to earn the 200 rep within that one year or is it enough to get 200 at some point after being a member for a year? And does 'a year' mean the very first 12 months or the last (sliding window of) 12 months?    I would assume that if you hit 200 reputation after you've already been around for a year, then you would get the Yearling badge. But I don't know.