I have a directory with huge number of files with different extensions. What I want to do is to move each extension to a folder with name the extension itself, and those files without extension move to a folder named unkown.  For example I have the files a.txt, b.txt ,a.pdf, b.pdf , a.mp4 , file, newfile ....  The result would be 4 dirs named txt, pdf, mp4 , unkonw  the txt dir contains the files a.txt, b.txt  the pdf dir contains the files a.pdf, b.pdf  the mp4 dir contains the files a.mp4  the unkonw dir contains the files file, newfile
I have some files with different extensions such as *.pdf, *.mp3, *.jpg and a few others. All of them are stored in a parent directory.  How can I get a list of all extensions, create some folders based on these  extensions and then move all files into their relevant folders?
Is there a way to find review articles by the keyword? When I search for papers using some keywords in academic databases (like Google Scholar), there are lots of papers, but I would like to read literature reviews first because I’m new in that area. (By literature reviews, I mean article-length papers that analyze existing work on a specific topic.)  So I think it would be helpful for me if there were a way to find literature reviews using the keyword or using the paper’s title. I want to categorize papers I’ve found by its document type (research, survey, review, etc).  What I've tried is using a specific academic database (ScienceDirect), which provides an advanced search, in which one can filter the paper by its type (original research article, review article, short survey, etc) – but I feel some limitations of this method. I think I can also do this by adding the word review to my keywords for searching or by reading a paper’s abstract, number of references and guessing whether it is review article or not.  Is there a more efficient way to find review articles by the keyword?  (My research area is computer science.)  UPDATE  "feel some limitations" in my post, I'm not sure but it seems that ScienceDirect only searches for literatures that belongs to ElseVier company. I think It doesn't cover the journal articles well, comparing to e.g) Google Scholar so I said I feel some limitations of it Where to find structure of objects that I can access in PHP snippets added to different parts of UI? How do I tell a script to wait for a process to start accepting requests on a port? I need a command that will wait for a process to start accepting requests on a specific port.    Is there something in linux that does that?  while (checkAlive -host localhost -port 13000 == false)   do some waiting  ... Find the sum $\frac{1}{2\cdot 3}+\frac{1}{3\cdot 4}+\dots+\frac{1}{99\cdot 100}$ Please help me calculate the following sum     $$\frac{1}{2\cdot 3}+\frac{1}{3\cdot 4}+\dots+\frac{1}{99\cdot 100}$$ Application-priority based automatic bandwidth distribution in Windows? Whenever my browser wants to download data, I want it to be granted as much of the bandwidth as it wants, while other applications must do with the leftover bandwidth; and when the browser is not transferring any data, other applications could be given the bandwidth. Something like the process priority in Windows task manager. Any method/software to accomplish this automatically? How do I recover or "undelete" files that I accidentally deleted? I've accidentally deleted some really important files on my machine, and I'm looking to find out how to recover them.  Using the Trash bins "restore" isn't an option, as the files aren't there (mostly likely I wasn't paying attention and permanently deleted them from there).  Is there any way that I can un-delete these files? How can I move or force a program installation to another location, even when unsupported? I have an SSD as my main Windows drive, with a 640GB 2.5" HDD, partitioned to store programs and user settings, and also to act as backup (it's the only thing I had lying around at the time of building my PC).  The problem is that whenever I install a program, it installs to C:\Program Files [(x86 for the 32 bit programs]\, although I have changed the environment variables. This wouldn't normally be an issue, however every installation program points its shortcut to my 640GB HDD.  The root layout of both drives:   To clarify:   Program files get installed to C:\ Program shortcuts are always pointed to Z:\, my 640GB HDD   Modifying the relevant environment variables doesn't do anything, I looked at , but however it only talks about modifying the registry and environment variables, which I have already done so.  I install to the Z:\ drive if the installation program lets me change the installation path, but however the installation programs sometimes don't let me change this.  Is there a way that I can force every program to install to the relevant location on Z:\, but at the same time move any programs currently installed to the new location? Perhaps I'm missing something here?  My target is to have every program installed on Z:/, with only the core Windows operating system on C:/.  Found ; would it be appropriate to use in my case? I would be able to move the entire Program Files (and its x86 version) to Z:\, without impacting on the performance.* I compile my project with VIsual Studio 2005 Express Edition, and get this linking error. Can anyone suggest how to solve that? Looking for old book, SF, artificial world, different zones for different species that visitors "inhabit" Hilbert, Gödel, and "God equations" - a 19th century lesson for 21st century physicists? It seems there are a lot of respected physicists appearing on pop-sci programs (discovery channel, science channel, etc.) these days spreading the gospel of   Three examples, quickly: 1) Many programs feature Michio Kaku saying that he is on a quest to find an equation, "perhaps just one inch long," which will "describe the whole universe."  2) Max Tegmark has come out with  in which he expresses the gut feeling that "nothing is off-limits" to science.  The subtitle of this book is My Quest for the Ultimate Nature of Reality.  3) In the series  there is talk about a search for the "God equation."  (A good counter-example would be Feynman, but his self-described "non-axiomatic" or "Babylonian" approach does not seem popular with physicists today.)  Is there any sense among physicists that it might be impossible to articulate the "ultimate nature of reality" in equations and formal logic?  It seems to me that physicists are following in the footsteps of the 19th century mathematicians (led by Hilbert) who were on a similar quest which was put to rest by Gödel's incompleteness theorems in 1931.  Is there any appreciation for how the Incompleteness Theorems might apply to physics?  Has any progress been made on  for the 20th century?  Shouldn't this be addressed before getting all worked up about a "God equation?" Disable ssh password authentication by user Is it possible to enable ssh password authentication for one user on a system and disable it for an other.  If you add  ChallengeResponseAuthentication no PasswordAuthentication no UsePAM no   to /etc/ssh/sshd_config you disable it for all users  Adding it to ~/.ssh/config doesn't seem to work Is there a 2D generalization of the coefficient of restitution? The  characterizes a collision in one dimension by relating the initial and final speeds of the particles involved,  $$C_R = -\frac{v_{2f} - v_{1f}}{v_{2i} - v_{1i}}$$   In a 2D collision, the velocity can be split into components parallel and perpendicular to the "plane of collision" (the plane tangent to the two objects' surfaces at their contact point), and the equation above applies to the perpendicular components of the velocities only. One could write  $$\begin{pmatrix}v_{2f\shortparallel} - v_{1f\shortparallel} \\ v_{2f\perp} - v_{1f\perp}\end{pmatrix} = \begin{pmatrix}1 &amp; 0 \\ 0 &amp; -C_R\end{pmatrix}\begin{pmatrix}v_{2i\shortparallel} - v_{1i\shortparallel} \\ v_{2i\perp} - v_{1i\perp}\end{pmatrix}$$   My question is, is it useful (i.e. does it produce a more accurate description of realistic 2D collisions) to generalize that matrix? Perhaps by allowing the top left element to be unequal to 1, or allowing nonzero off-diagonal elements? Or is there some nonlinear relation that works better?  As usual, if you know of any relevant published research, references would be much appreciated. Can a dementor decide which people around it will be affected by its magic? Quoting from  and : From a :  Samantha: Was snape the only death eater who could produce a full patronus J.K. Rowling: Yes, because a Patronus is used against things that the Death Eaters generally generate, or fight alongside. They would not need Patronuses.  I always had the impression that just the presence of a dementor should have an effect on any human around, DE or otherwise. However, this quote makes it sound like DE's are exempt from the effect of the dementors. However, from Sirius's description in book 3, we know every prisoner in Azkaban was affected by dementors, which can further be corroborated by the fact of how much Barty Crouch, Jr. was scared of being thrown into Azkaban. Moreover, if the dementors didn't affect the DE's at all, throwing them in Azkaban wouldn't be much of a punishment either. So, Can dementors decide who to affect or not? Why is $(0, 0)$ not a minimum of $f(x, y) = (y-3x^2)(y-x^2)$? There is an exercise in my lists about those functions: $$f(x, y) = (y-3x^2)(y-x^2) = 3 x^4-4 x^2 y+y^2$$  $$g(t) = f(vt) = f(at, bt); a, b \in \mathbf{R}$$  It asks me to prove that $t = 0$ is a local minimum of $g$ for all $a, b \in \mathbf{R}$  I did it easily: $$g(t) = 3 a^4 t^4-4 a^2 t^2 b t+b^2 t^2$$ $$g&#39;(t) = 2 b^2 t-12 a^2 b t^2+12 a^4 t^3$$ $$g&#39;&#39;(t) = 2 b^2-24 a^2 b t+36 a^4 t^2$$  It is a critical point: $$g&#39;(0) = 0; \forall a, b$$  Its increasing for all a, b: $$g&#39;&#39;(0) = 2b^2 &gt; 0; \forall b \ne 0$$ and $$b = 0 \implies g(t) = 3 a^4 t^4$$ which has only one minimum, at $0$, and no maximum  However, it also asks me to prove that $(0, 0)$ is not a local minimum of $f$.  How can this be possible? I mean, if $(0, 0)$ is a minimum over every straight line that passes through it, then, in this point, $f$ should be increasing in all directions, no? Is there a regular expression to validate an email address in JavaScript? Validationengine jquery not working properly for localization How to read contacts on Android 2.0 Two envelope problem revisited I was thinking of this problem.  I believe the solution and I think I understand it, but if I take the following approach I'm completely confused. Problem 1:  I will offer you the following game. You pay me \$10 and I will flip a fair coin. Heads I give you \$5 and Tails I give you \$20. The expectation is \$12.5 so you will always play the game.  Problem 2:  I will give you an envelope with \$10, the envelope is open and you can check. I then show you another envelope, closed this time and tell you: This envelope either has \$5 or $20 in it with equal probability. Do you want to swap? I feel this is exactly the same as problem 1, you forgo \$10 for a \$5 or a \$20, so again you will always switch.  Problem 3:  I do the same as above but close the envelopes. So you don't know there are $10 but some amount X. I tell you the other envelope has double or half. Now if you follow the same logic you want  to switch. This is the envelope paradox.  What changed when I closed the envelope?? EDIT: Some have argued that problem 3 is not the envelope problem and I'm going to try and provide below why I think it is by analysing how each views the game. Also, it gives a better set up for the game. Providing some clarification for Problem 3: From the perspective of the person organising the game:  I hold 2 envelopes. In one I put \$10 close it and give it to the player. I then tell him, I have one more envelope that has either double or half the amount of the envelope I just gave you. Do you want to switch? I then proceed to flip a fair coin and Heads I put \$5 in and Tails I put \$20. And hand him the envelope. I then ask him. The envelope you just gave me has twice or half the amount of the envelope you are holding. Do you want to switch?  From the perspective of the player:  I am given an envelope and told there is another envelope that has double or half the amount with equal probability. Do I want to switch. I think sure I have $X$, hence $\frac{1}{2}(\frac{1}{2}X + 2X) &gt; X$ so I want to switch. I get the envelope and all of a sudden I am facing the exact same situation. I want to switch again as the other envelope has either double or half the amount. About two weeks ago I had a problem with my PC that my brother wrote a question about at .  I still haven't solved the problem, so my PC is unusable now.  Now I think that it would be simpler to re-install both Win7 &amp; Ubuntu than repair them, but there're some data on their partitions. I want to recover this data.  These partitions are not mountable for some reason. I don't know why.  sudo fdisk -l about the problematic partitions:     Device    Boot      Start         End      Blocks   Id  System /dev/sda1            2048     147912703    73955328   83 Linux /dev/sdb2            206848   174079999    86936576    7  HPFS/NTFS/exFAT   And in GParted:      And the error of the mount command:  Failed to mount '/dev/sdb2': Invalid argument The device '/dev/sdb2' doesn't seem to have a valid NTFS. Maybe the wrong device is used? Or the whole disk instead of a partition (e.g. /dev/sda, not /dev/sda1)? Or the other way around?   And the exact same message for /dev/sda1  How can I recover my data from those HDDs?  EDIT     I have tried to specify the type of the drive:  $ sudo mount -t ext4 /dev/sda1 /olddisk mount: wrong fs type, bad option, bad superblock on /dev/sda1,        missing codepage or helper program, or other error        In some cases useful info is found in syslog - try        dmesg | tail  or so $ sudo mount -t ntfs /dev/sdb2 /olddisk NTFS signature is missing. Failed to mount '/dev/sdb2': Invalid argument The device '/dev/sdb2' doesn't seem to have a valid NTFS. Maybe the wrong device is used? Or the whole disk instead of a partition (e.g. /dev/sda, not /dev/sda1)? Or the other way around?   EDIT     sudo ntfsfix /dev/sdb2 returns:  Mounting volume... NTFS signature is missing. FAILED Attempting to correct errors... NTFS signature is missing. FAILED Failed to startup volume: Invalid argument NTFS signature is missing. Trying the alternate boot sector Unrecoverable error Volume is corrupt. You should run chkdsk. How to create a progress bar?