I understand that   sudo cd /directory   will return:  sudo: cd: command not found   because cd is a shell builtin and not a binary. But then, why does   sudo echo 'this is a test'   works fine?  What is really going on here? How does sudo find the command echo if it's not a shell?
$ which echo echo: shell built-in command. $ which ls /bin/ls $ which cat /bin/cat   Why is echo not an independent utility like ls, ps, cat etc? Why is it shell specific? Any good reasons?
Does the output bypass capacitor of an LM7805 double as a decoupling capacitor? I'm using a 5v linear regulator (specifically an LM7805) that outputs directly to an ATMEGA328P. According to the  (page 23) input and output bypass capacitors should be used, as seen below, to tame peaks and ensure stability.    It is good practice to also include a decoupling capacitor in front of an IC, in this case an ATMEGA328. Does the 0.1μF capacitor on the output side of the LM7805 act as a decoupling capacitor if the regulator feeds into the IC directly after the output bypass capacitor? markdown doesn't work properly What is the unisex form of a word like fisherman? Do you have to use fisherman and fisherwoman separately, or is fisherperson acceptable? I couldn’t find a dictionary with the word …  In general, what do you do when a word does not have a unisex form? Punctuation with units I remember reading somewhere that if a unit is abbreviated as one character, there must not be a space between the number and the unit (e.g., 5m, 26K). If the unit is abbreviated as two or more Characters, there must be a space between the number and the unit (e.g., "10 km", "USD 5").   Can you please help me find the source again? Is this recommendation correct? Is a general GRE score of X sufficient for entry to postgraduate degree Y? Question: I got general GRE scores of VR (verbal reasoning), QR (quantitative reasoning), and AW (analytical writing).  Is this a good score to apply for entry to postgraduate degree in field X?  How will this score look to the selection committee?    Note: This is an intentionally generic GRE question (with unspecified scores and field of study) which is intended as a template for a large number of questions asked on this forum regarding evaluating the scores on the general GRE test (e.g., , , , , , , , and ).  This question seeks answers that are applicable for an applicant for graduate-level programs in any field, based on any scores in the GRE general test.  The goal of this question is to provide a general reference to avoid the need for specific questions with particular scores/field of study. If I were to use the sentence "There are lots of John Smiths" in the world, would that be the correct use for saying that there are a lot of people named John Smith in the world?  I don't think there should be an apostrophe as that would imply ownership of something.  If my first example is correct, then what would you do if the name referenced already ended with an 's'? I am asked to complete my withdrawal transaction with COT fee of 1200 dollars I was marketed by a lady online on some investment packages in bitcoin. ($200 to become $2500 in one week of trade). I indicated interest in this. She took me to a trading website to sign up.  I deposited $200 at the start. After trading for 2 days with earnings, they called me to upgrade the account with $450 which I did. They then traded for 1 week and the account balance became $6786.    I requested to withdraw $6000 from my account and they told me to bring a COT fee of $1200 to complete my withdrawal.  Please help me do a background check on them. Are they real or fake? Check the registration of the company if it is real. The marketer told me the company will pay her from the COT fee. Java Strings: "String s = new String("silly");" My equation is not showing big bracket and not showing in next line How to get less spacing in math mode LaTeX commands like this:  Here again, four different simulations are run on networks of size  $C^{G} = 25 \times\ 25 = 625$, $C^{G} = 50 \times\ 50 = 2500$, $C^{G} = 250 \times\ 250 = 62500$, and $C^{G} = 500 \times\ 500 = 250000$...   When compiled generate the following:    The spacing in math mode really irritates me. There's too much white space around the equal sign, and the multiplication sign has more right padding than left padding. Is there any way to reduce this spacing? Is this algebraic identity obvious? $\sum_{i=1}^n \prod_{j\neq i} {\lambda_j\over \lambda_j-\lambda_i}=1$ If $\lambda_1,\dots,\lambda_n$ are distinct positive real numbers, then  $$\sum_{i=1}^n \prod_{j\neq i} {\lambda_j\over \lambda_j-\lambda_i}=1.$$ This identity follows from a probability calculation that you can find at the  top of page 311 in the 10th edition of Introduction to Probability Models by Sheldon Ross.   Is there a slick or obvious explanation for this identity?   This  question is sort of similar to ; clearly algebra is not my strong suit! I understand there is a method for solving simultaneous modular equations. For example; $$x = 2 \mod{3}$$ $$x = 3 \mod{5}$$ $$x = 2 \mod{7}$$ We find numbers equal to the product of every given modulo except one of them - giving $5 \cdot 7$, $3 \cdot 7$ and $3 \cdot 5$. We then find the multiplicative inverses of these numbers with modulo equal to the number missing from the product. The numbers found are then 2, 1 and 1 in this case. The value of x is then given by: $$x = 2 \cdot (5 \cdot 7) \cdot 2 + 3 \cdot (3 \cdot 7) \cdot 1 + 2 \cdot (3 \cdot 5) \cdot 1 = 233 = 23 \mod{3\cdot5\cdot7}$$  But I do not understand how this method correctly gives the value of $x$. I understand that the Chinese remainder theorem proves that there is a unique value of $0\le x \lt 3\cdot5\cdot7 \mod{3\cdot5\cdot7}$ but can someone please explain why this method finds this value of x? During the last phase of layout I frequently get a single line or two on a separate page. Rather then pulling the whole paragraph on that last page I would like to "squeeze" the lines on the previous page a bit.  Is there a way to mark the current page to be squeezed a bit if necessary, but let LaTeX reset this marking automatically after the page is done? Correlations with unordered categorical variables I have a dataframe with many observations and many variables. Some of them are categorical (unordered) and the others are numerical.  I'm looking for associations between these variables. I've been able to compute correlation for numerical variables (Spearman's correlation) but :   I don't know how to measure correlation between unordered categorical variables. I don't know how to measure correlation between unordered categorical variables and numerical variables.   Does anyone know how this could be done? If so, are there R functions implementing these methods? how to make a 360 video (turntable) of an Object using a python script Let $E$ be measurable and define $f:E\rightarrow\mathbb{R}$ such that $\{x\in E : f(x)>c\}$ is measurable for all $c\in\mathbb{Q}$, is $f$ measurable? Let $E$ be measurable and define $f:E\rightarrow\mathbb{R}$ such that $\{x\in E : f(x)&gt;c\}$ is measurable for all $c\in\mathbb{Q}$, is $f$ measurable?  There are a number of equivalent definitions for the measurability of a function and the most obvious one would be to show that $\{x\in E : f(x)&gt;c\}$ is measurable for all $c\in\mathbb{R}$.  Thus my strategy has been to consider an arbitrary irrational $y$ and use the density of the rationals in the reals to show that there exists some open set $O$ such that $m^*(O-\{x\in E : f(x)&gt;y\})&lt; \varepsilon$.  I would do this by choosing some rational $q&lt;y$, close enough to $y$, such that the set of values in $E$ which get sent under $f$ to values strictly greater than $q$ and less than or equal to $y$ is small enough.  But that doesn't in general seem possible since I could keep sending intervals of some fixed positive length to smaller and smaller regions just beneath $y$.  However conversely, such a function would not be enough for a counter example, since finding such a function only rules out this strategy, but doesn't necessarily entail non-measurability.  Is there a better definition of the measurability of a set I should use? or does the statement actually not imply measurability?  Thanks. Here is a question that's been bothering me since I was a sophomore in university, and should have probably asked before graduating:  In analytic (Lagrangian) mechanics, the derivation of the Euler-Lagrange equations from the principle of least action assumes that the start and end coordinates at the initial and final times are known. As a consequence, any variation on the physical path must vanish at its boundaries. This conveniently cancels out the contributions of the boundary terms after integration by parts, and setting the requirement for minimal action, we obtain the E.L. equations.  This is all nice and dandy, but our intention is finding the location of a particle at a time in the future, which we do not know a priori; after we derive any equations of motion for a system, we solve them by applying initial values instead of boundary conditions.   How are these two approaches consistent? Can I delete user directory after deleting user? The reason I ask is because I recently made the mistake of installing Oracle 12c on my sub-performance laptop. Noticing the excessive amount of resources this added up to on startup, I decided to uninstall it.  What I failed to see through, however, was the fact that it created a new Windows user account in order for the initial installation to work out. In my case, it was mandatory because I only had an administrator account and I didn't see the need to use the built-in account. So, after failing to successfully install 12c twice, I wound up creating not just one, but two Windows user accounts. This had to do with something in regards to how Oracle sets up the Oracle Home business and whatnot, but I have no idea what any of that detailed, so I just went ahead and did it.  After uninstalling what I could in regards to Oracle and the database, I decided the next thing to do would be to remove the created users.  Having Windows 10 Home installed, I couldn't use the local users &amp; groups view/tool to delete these from the GUI. SO, I did the next best thing and Googled a solution. In my case, I used the following command:  net user username /DELETE   When I executed the command, the console gave the response of having successfully deleted the account for both accounts specified.  To verify that this had worked, I went to the users directory located in %SYSTEMROOT%/Users/ and came to find that the user directories were still there.  What does this mean and if I should delete them, will anything bad happen?  Can I even delete these directories?  Regards,  --T.R.G What is the "En passant" rule in chess? How useful is that rule and how many times we can use that in one game?  Under what conditions can the en passant rule be used?  How often does it come up and is it a good idea to use it? How to set Command Block(s) to test for a particular time and output a message? I simply want one command block to test for the time of day or night (e.g. time = 18000) and output a message in the chat to everyone if that time returns true.  I was trying a simple set-up with two command blocks and a comparator in the middle, but I'm a beginner and am obviously missing the correct syntax (especially to test for a particular time of day, and if true, then trigger the say "message" block).  ETA: Kudos to @Ben for the Daylight Sensor/Redstone idea, but I'd really prefer a Command Block solution for the above, since my plan is to output several messages during the day and night cycle at very specific times in the world. Thanks.