What does ! mean in the statement if [ ! -n "$1" ]
Usage of -n and -z in test built in - Bash
I already read it from manual but I can't see difference..  su - change user ID or become superuser  sudo -s [command]   The -s (shell) option runs the shell specified by the SHELL environment variable if it is set or the shell as specified in passwd(5).  If a                    command is specified, it is passed to the shell for execution.  Otherwise, an interactive shell is executed.  sudo -i disappear description in manual Scorched3d worked then stopped. Unistalled and reinstalled did not help. Running Ubuntu 16.04.04LTS. I think it was after installing new release.  I think the problem is the Ubuntu 16.04.4LTS. The newer version has no Scorched3d in the Ubuntu Software Center. I have 3 systems. After updating to new version. Scorched3D will not install and work after updating.  ron@RonsComputer:~$ sudo objdump -p $(type -p scorched3d) | grep NEEDED  NEEDED libwx_gtk2u_adv-3.0.so.0  NEEDED libwx_gtk2u_core-3.0.so.0 NEEDED libwx_baseu-3.0.so.0 NEEDED libfreetype.so.6 NEEDED libz.so.1 NEEDED libSDL-1.2.so.0 NEEDED libSDL_net-1.2.so.0 NEEDED libexpat.so.1  NEEDED libstdc++.so.6 NEEDED libm.so.6 NEEDED libgcc_s.so.1 NEEDED libpthread.so.0 NEEDED libc.so.6   ron@ron-desktop ~ $ objdump -p $(type -p scorched3d) | grep NEEDED | awk '{print $2}' | xargs -n 1 dpkg -S  libwxgtk3.0-0v5:amd64: /usr/lib/x86_64-linux-gnu/libwx_gtk2u_adv-3.0.so.0.2.0 libwxgtk3.0-0v5:amd64: /usr/lib/x86_64-linux-gnu/libwx_gtk2u_adv-3.0.so.0 libwxgtk3.0-0v5:amd64: /usr/lib/x86_64-linux-gnu/libwx_gtk2u_core-3.0.so.0.2.0 libwxgtk3.0-0v5:amd64: /usr/lib/x86_64-linux-gnu/libwx_gtk2u_core-3.0.so.0 libwxbase3.0-0v5:amd64: /usr/lib/x86_64-linux-gnu/libwx_baseu-3.0.so.0.2.0 libwxbase3.0-0v5:amd64: /usr/lib/x86_64-linux-gnu/libwx_baseu-3.0.so.0 libfreetype6:amd64: /usr/lib/x86_64-linux-gnu/libfreetype.so.6.12.1 libfreetype6:i386: /usr/lib/i386-linux-gnu/libfreetype.so.6 libfreetype6:amd64: /usr/lib/x86_64-linux-gnu/libfreetype.so.6 libfreetype6:i386: /usr/lib/i386-linux-gnu/libfreetype.so.6.12.1 zlib1g:i386: /lib/i386-linux-gnu/libz.so.1.2.8 zlib1g:amd64: /lib/x86_64-linux-gnu/libz.so.1 zlib1g:i386: /lib/i386-linux-gnu/libz.so.1 zlib1g:amd64: /lib/x86_64-linux-gnu/libz.so.1.2.8 libsdl1.2debian:amd64: /usr/lib/x86_64-linux-gnu/libSDL-1.2.so.0.11.4 libsdl1.2debian:i386: /usr/lib/i386-linux-gnu/libSDL-1.2.so.0 libsdl1.2debian:i386: /usr/lib/i386-linux-gnu/libSDL-1.2.so.0.11.4 libsdl1.2debian:amd64: /usr/lib/x86_64-linux-gnu/libSDL-1.2.so.0 libsdl-net1.2:amd64: /usr/lib/x86_64-linux-gnu/libSDL_net-1.2.so.0 libsdl-net1.2:i386: /usr/lib/i386-linux-gnu/libSDL_net-1.2.so.0 libsdl-net1.2:amd64: /usr/lib/x86_64-linux-gnu/libSDL_net-1.2.so.0.8.0 libsdl-net1.2:i386: /usr/lib/i386-linux-gnu/libSDL_net-1.2.so.0.8.0 libexpat1:i386: /lib/i386-linux-gnu/libexpat.so.1.6.0 libexpat1:amd64: /lib/x86_64-linux-gnu/libexpat.so.1 libexpat1:amd64: /lib/x86_64-linux-gnu/libexpat.so.1.6.0 libexpat1:i386: /lib/i386-linux-gnu/libexpat.so.1 libstdc++6:amd64: /usr/share/gdb/auto-load/usr/lib/x86_64-linux-gnu/libstdc++.so.6.0.21-gdb.py libstdc++6:i386: /usr/lib/i386-linux-gnu/libstdc++.so.6 libstdc++6:amd64: /usr/lib/x86_64-linux-gnu/libstdc++.so.6 libstdc++6:amd64: /usr/lib/x86_64-linux-gnu/libstdc++.so.6.0.21 libstdc++6:i386: /usr/lib/i386-linux-gnu/libstdc++.so.6.0.21 libstdc++6:i386: /usr/share/gdb/auto-load/usr/lib/i386-linux-gnu/libstdc++.so.6.0.21-gdb.py libc6:amd64: /lib/x86_64-linux-gnu/libm.so.6 libc6:i386: /lib/i386-linux-gnu/libm.so.6 libgcc1:amd64: /lib/x86_64-linux-gnu/libgcc_s.so.1 libgcc1:i386: /lib/i386-linux-gnu/libgcc_s.so.1 libc6:i386: /lib/i386-linux-gnu/libpthread.so.0 libc6:amd64: /lib/x86_64-linux-gnu/libpthread.so.0 libc6:i386: /lib/i386-linux-gnu/libc.so.6 libc6:amd64: /lib/x86_64-linux-gnu/libc.so.6 ron@ron-desktop ~ $ If I am shooting the 8-ball for a win, and my opponent has a ball near the pocket I'm aiming for, can I call something like "8-ball off the 2 ball into the corner pocket"?  I thought this was allowed, but a friend says this is an automatic loss and that the 8-ball must never touch another ball before going into the pocket.  Various pool rules aren't clear for me on this scenario. Previous posts                  As of today, the Moderator Flag Dashboard is officially graduated and the old version sent to the smelter's yard.  Based on stats from the past month, virtually all moderators were already on the new UI (thank you) so you hopefully won't notice any change.  That said, I would like to highlight the handful of improvements we made over the last month and a half based on your feedback:   A more responsive navigation bar at the top of moderator pages, improving the mobile experience. Similarly, , increasing room on the screen for the first question. . .  Not only do the headers look better, they now function better.  Now you scroll to and highlight the post/comment each time you click the link, not just the first time. .  Posts by the same user are grouped together and ordered newest first. .  We eliminated the VLQ (auto) side effect so now "Resolve all flags (auto)" doesn't do anything surprising.  If you still want to leave a comment or decline, you can do so with the buttons next to the individual flags.   Bugs and Feature Requests  Since this project is officially launched, all bugs and feature requests should be done in the form of questions tagged  on MSE, not answers on this post.  Feel free to post an answer here if you have specific concerns about the release process. What is the CVE-2014-6271 bash vulnerability (Shellshock) and how do I fix it? Tools to get a pictorial function call graph of code Why am I getting "No such file or directory" when I try to execute a binary? Eigenvalues of a matrix whose square equals its transpose Let $A$ be a $n\times n$ matrix with $A^2=A^t$. Show that every real eigen value of $A$ is either $ 0$ or $1$ I can't type a “b” when I'm in the command line Prove every odd integer is the difference of two squares I know that I should use the definition of an odd integer ($2k+1$), but that's about it.  Thanks in advance! This is a  about hostname-awareness and proxying.   I know that some protocols are hostname-aware; that is, when I connect to the HTTP server at www.example.com it knows I want www.example.com's HTTP service, not www.example.net's, even though they are on the same IP address.  How can I do this for protocol foo?  (Temporary note: this question appears pursuant to .) Can a possessive S be attached to nouns that are not human beings (or animals)? Can a possessive S be attached to nouns that are not human beings (or animals)?  For example, instead of saying "the back of the chair", can I say "the chair's back"?   I remember learning that not everything can get a possessive s, but this issue is not clear to me. What's the batched Refactor Fields tool "field mapping" syntax in QGIS? In QGIS, there is this nice tool "Refactor Fields" in the Processing Toolbox :    Using it on a single layer is fairly straightforward.  However, when you plan on using it in a batch mode, one can see the "Fields mapping" textbox. I'm looking for an example of the syntax to be used there.  I haven't found any specific documentation yet. Boy asks 'How about pie?' I am looking for the title of a 1950s science fiction movie, involving an astronomer trying to decode some extraterrestrial signal, where the juvenile (male) character asks 'how about pi?' which all the adults interpret as a foolish 'how about pie?' question. What is wrong with code snippets/blocks on Stack Overflow? I wasn't following Meta Stack Overflow too closely so maybe something was changed that I'm not aware of. But each time I paste a snippet from a Python console I'm getting wrong formatting. What I'm doing wrong? It seems that &gt;&gt;&gt; is confusing for Stack Overflow. I've tried to escape it with backslashes, and it was working fine in preview but doesn't work after the question is rendered.  I was able to observe that problem on: recent Chrome (Windows, Mac), Safari 4 (Mac).  Here is  I wasn't able to make right.  Funny, I think the snippets are rendered just fine on Meta Stack Overflow. Here is one:  &gt;&gt;&gt; def throw(): raise Exception()  ...  &gt;&gt;&gt; a=1 &gt;&gt;&gt; a=throw() Traceback (most recent call last):   File "&lt;stdin&gt;", line 1, in &lt;module&gt;   File "&lt;stdin&gt;", line 1, in throw Exception &gt;&gt;&gt; a 1 A concise definition of a frame of reference in Newtonian mechanics? I've read  on frame of reference and also followed all of the references cited in the text (Salençon, Brillouin, Norton, etc) but I'm struggling to find any concise definition in all of that.   I would like a concise definition for a frame of reference in the context of Newtonian mechanics. This definition should not involve any additional qualifiers such as inertial and must be mature enough as to differentiate a frame of reference and a coordinate system. Is there one such definition? This is solely a reference request. I have heard a few versions of the following theorem:     If the joint moment generating function $\mathbb{E}[e^{uX+vY}] = \mathbb{E}[e^{uX}]\mathbb{E}[e^{vY}]$ whenever the expectations are finite, then $X,Y$ are independent.   And there is a similar version for characteristic functions. Could anyone provide me a serious reference which proves one or both of these theorems? Proving $\int_{0}^{\infty} \mathrm{e}^{-x^2} dx = \frac{\sqrt \pi}{2}$ How to prove  $$\int_{0}^{\infty} \mathrm{e}^{-x^2}\, dx = \frac{\sqrt \pi}{2}$$ how to get line spacing greater than one and half spacing and less than double space Does anyone know how to get line spacing in a paragraph to be greater than one and half spacing and less than double spacing? I tried \renewcommand{\baselinestretch}{value} but it did not work. "inputenc Error: Unicode char \u8" error while trying to write a degree symbol (invisible character) No matter how I try to do it I always get the following error :      ! Package inputenc Error: Unicode char \u8:­ not set up for use with LaTeX.    I have tried using ­­­$^{\circ}$, \deg, \textdegree, pasting the ° symbol directly, to no avail.  Here is the header of my document, in case one of those could be causing the errors :  \usepackage[utf8]{inputenc} \usepackage[T1]{fontenc} \usepackage{lmodern} \usepackage[francais]{babel} %\FrenchItemizeSpacingfalse \frenchbsetup{CompactItemize=false} \usepackage{amsmath} \usepackage{amsfonts} \usepackage{amsthm}