No error , No gain

What is this? This is a collection of questions that come up every now and then about syntax in PHP. This is also a Community Wiki, so everyone is invited to participate in maintaining this list. Why is this? It used to be hard to find questions about operators and other syntax tokens.¹ The main idea is to have links to existing questions on Stack Overflow, so it's easier for us to reference the..

Also how do LEFT JOIN, RIGHT JOIN and FULL JOIN fit in? Assuming you're joining on columns with no duplicates, which is a very common case: An inner join of A and B gives the result of A intersect B, i.e. the inner part of a Venn diagram intersection. An outer join of A and B gives the results of A union B, i.e. the outer parts of a Venn diagram union. Examples Suppose you have two tables, with ..

I forked a project, applied several fixes and created a pull request which was accepted. A few days later, another change was made by another contributor. So my fork doesn't contain that change. How can I get that change into my fork? Do I need to delete and re-create my fork when I have further changes to contribute? Or is there an update button? In your local clone of your forked repository, y..

How do you delete a Git tag that has already been pushed? You can push an 'empty' reference to the remote tag name: git push origin :tagname Or, more expressively, use the --delete option (or -d if your git version is older than 1.8.0): git push --delete origin tagname Note that git has tag namespace and branch namespace so you may use the same name for a branch and for a tag. If you want to mak..

How do I make the first letter of a string uppercase, but not change the case of any of the other letters? For example: "this is a test" → "This is a test" "the Eiffel Tower" → "The Eiffel Tower" "/index.html" → "/index.html" The basic solution is: function capitalizeFirstLetter(string) { return string.charAt(0).toUpperCase() + string.slice(1); } console.log(capitalizeFirstLetter('foo')); // Foo..

What command can be used to check if a directory exists or not, within a Bash shell script? To check if a directory exists in a shell script, you can use the following: if [ -d "$DIRECTORY" ]; then # Control will enter here if $DIRECTORY exists. fi Or to check if a directory doesn't exist: if [ ! -d "$DIRECTORY" ]; then # Control will enter here if $DIRECTORY doesn't exist. fi However, as Jon Er..

I'd like to do something like this to tick a checkbox using jQuery: $(".myCheckBox").checked(true); or $(".myCheckBox").selected(true); Does such a thing exist? Modern jQuery Use .prop(): $('.myCheckbox').prop('checked', true); $('.myCheckbox').prop('checked', false); DOM API If you're working with just one element, you can always just access the underlying HTMLInputElement and modify its .check..

What are the differences between a HashMap and a Hashtable in Java? Which is more efficient for non-threaded applications? There are several differences between HashMap and Hashtable in Java: Hashtable is synchronized, whereas HashMap is not. This makes HashMap better for non-threaded applications, as unsynchronized Objects typically perform better than synchronized ones. Hashtable does not allo..

Something similar to Unix's timestamp, that is a single number that represents the current time and date. Either as a number or a string. Short & Snazzy: + new Date() A unary operator like plus triggers the valueOf method in the Date object and it returns the timestamp (without any alteration). Details: On almost all current browsers you can use Date.now() to get the UTC timestamp in millisecond..

I keep rereading the Docker documentation to try to understand the difference between Docker and a full VM. How does it manage to provide a full filesystem, isolated networking environment, etc. without being as heavy? Why is deploying software to a Docker image (if that's the right term) easier than simply deploying to a consistent production environment? Docker originally used LinuX Containers..

After I upgraded to the latest stable node and npm, I tried npm install moment --save. It saves the entry in the package.json with the caret ^ prefix. Previously, it was a tilde ~ prefix. Why are these changes made in npm? What is the difference between tilde ~ and caret ^? What are the advantages over others? See the NPM docs and semver docs: ~version “Approximately equivalent to version”, will..

How can I add a blank directory (that contains no files) to a Git repository? Another way to make a directory stay (almost) empty (in the repository) is to create a .gitignore file inside that directory that contains these four lines: # Ignore everything in this directory * # Except this file !.gitignore Then you don't have to get the order right the way that you have to do in m104's solution. T..

Is there a shortcut to make a simple list out of a list of lists in Python? I can do it in a for loop, but is there some cool "one-liner"? I tried it with functools.reduce(): from functools import reduce l = [[1, 2, 3], [4, 5, 6], [7], [8, 9]] reduce(lambda x, y: x.extend(y), l) But I get this error: Traceback (most recent call last): File "", line 1, in File "", line 1, in AttributeError: 'None..

I have a master and a development branch, both pushed to GitHub. I've cloned, pulled, and fetched, but I remain unable to get anything other than the master branch back. I'm sure I'm missing something obvious, but I have read the manual and I'm getting no joy at all. First, clone a remote Git repository and cd into it: $ git clone git://example.com/myproject $ cd myproject Next, look at the loca..

How do I access the index in a for loop like the following? ints = [8, 23, 45, 12, 78] for i in ints: print('item #{} = {}'.format(???, i)) I want to get this output: item #1 = 8 item #2 = 23 item #3 = 45 item #4 = 12 item #5 = 78 When I loop through it using a for loop, how do I access the loop index, from 1 to 5 in this case? Using an additional state variable, such as an index variable (which..

I need a good explanation (references are a plus) on Python's slice notation. To me, this notation needs a bit of picking up. It looks extremely powerful, but I haven't quite got my head around it. It's pretty simple really: a[start:stop] # items start through stop-1 a[start:] # items start through the rest of the array a[:stop] # items from the beginning through stop-1 a[:] # a copy of the whol..

What is the most concise and efficient way to find out if a JavaScript array contains a value? This is the only way I know to do it: function contains(a, obj) { for (var i = 0; i < a.length; i++) { if (a[i] === obj) { return true; } } return false; } Is there a better and more concise way to accomplish this? Modern browsers have Array#includes, which does exactly that and is widely supported by ..

I know it's possible to match a word and then reverse the matches using other tools (e.g. grep -v). However, is it possible to match lines that do not contain a specific word, e.g. hede, using a regular expression? Input: hoho hihi haha hede Code: grep "[^R]+|R+(?!egex Hero))*$ resulting in a small performance gain. But the overall most readable and performance-wise fastest solution seems to be ..

Yesterday I was pairing the socks from the clean laundry and figured out the way I was doing it is not very efficient. I was doing a naive search — picking one sock and "iterating" the pile in order to find its pair. This requires iterating over n/2 * n/4 = n2/8 socks on average. As a computer scientist I was thinking what I could do? Sorting (according to size/color/...) of course came to mind ..

How can I squash my last X commits together into one commit using Git? You can do this fairly easily without git rebase or git merge --squash. In this example, we'll squash the last 3 commits. If you want to write the new commit message from scratch, this suffices: git reset --soft HEAD~3 && git commit If you want to start editing the new commit message with a concatenation of the existing commi..