Tutorial by Examples: b

This is a continuous collector that uses the hadoop fs -du -s /hbase/* command to get details about the HDFS disk usage. This metric is very useful for tracking space in an OpenTSDB system. #!/bin/bash while true; do while read -r bytes raw_bytes path; do echo "hdfs.du $(date +&...

The following demo features an <output> element's use of the [for] and [form] attributes. Keep in mind, <output> needs JavaScript in order to function. Inline JavaScript is commonly used in forms as this example demonstrates. Although the <input> elements are type="number&quot...

<output name="out1" form="form1" for="inp1 inp2"></output>

To recover a deleted branch you need to find the commit which was the head of your deleted branch by running git reflog You can then recreate the branch by running git checkout -b <branch-name> <sha1-of-commit> You will not be able to recover deleted branches if git's garbage col...

var wsHost = "ws://my-sites-url.com/path/to/web-socket-handler"; var ws = new WebSocket(wsHost);

A lambda expression evaluated in a class' member function is implicitly a friend of that class: class Foo { private: int i; public: Foo(int val) : i(val) {} // definition of a member function void Test() { auto lamb = [](Foo &foo, int val) ...

Some regex flavors (Perl, PCRE, Oniguruma, Boost) only support fixed-length lookbehinds, but offer the \K feature, which can be used to simulate variable-length lookbehind at the start of a pattern. Upon encountering a \K, the matched text up to this point is discarded, and only the text matching th...

Variable substitutions should only be used inside double quotes. calculation='2 * 3' echo "$calculation" # prints 2 * 3 echo $calculation # prints 2, the list of files in the current directory, and 3 echo "$(($calculation))" # prints 6 Outside of doubl...

The & operator will perform a binary AND, where a bit is copied if it exists in both operands. That means: # 0 & 0 = 0 # 0 & 1 = 0 # 1 & 0 = 0 # 1 & 1 = 1 # 60 = 0b111100 # 30 = 0b011110 60 & 30 # Out: 28 # 28 = 0b11100 bin(60 & 30) # Out: 0b11100

The | operator will perform a binary "or," where a bit is copied if it exists in either operand. That means: # 0 | 0 = 0 # 0 | 1 = 1 # 1 | 0 = 1 # 1 | 1 = 1 # 60 = 0b111100 # 30 = 0b011110 60 | 30 # Out: 62 # 62 = 0b111110 bin(60 | 30) # Out: 0b111110

The ^ operator will perform a binary XOR in which a binary 1 is copied if and only if it is the value of exactly one operand. Another way of stating this is that the result is 1 only if the operands are different. Examples include: # 0 ^ 0 = 0 # 0 ^ 1 = 1 # 1 ^ 0 = 1 # 1 ^ 1 = 0 # 60 = 0b1111...

The << operator will perform a bitwise "left shift," where the left operand's value is moved left by the number of bits given by the right operand. # 2 = 0b10 2 << 2 # Out: 8 # 8 = 0b1000 bin(2 << 2) # Out: 0b1000 Performing a left bit shift of 1 is equivalent ...

The >> operator will perform a bitwise "right shift," where the left operand's value is moved right by the number of bits given by the right operand. # 8 = 0b1000 8 >> 2 # Out: 2 # 2 = 0b10 bin(8 >> 2) # Out: 0b10 Performing a right bit shift of 1 is equivalent...

Gradients are new image types, added in CSS3. As an image, gradients are set with the background-image property, or the background shorthand. There are two types of gradient functions, linear and radial. Each type has a non-repeating variant and a repeating variant: linear-gradient() repeating-...

You shouldn't call NSLog without a literal format string like this: NSLog(variable); // Dangerous code! If the variable is not an NSString, the program will crash, because NSLog expects an NSString. If the variable is an NSString, it will work unless your string contains a %. NSLog will pars...

We can illustrate this problem with the following pseudo-code function foo() { global $bob; $bob->doSomething(); } Your first question here is an obvious one Where did $bob come from? Are you confused? Good. You've just learned why globals are confusing and considered a bad p...

Bool is a Boolean type with two possible values: true and false. let aTrueBool = true let aFalseBool = false Bools are used in control-flow statements as conditions. The if statement uses a Boolean condition to determine which block of code to run: func test(_ someBoolean: Bool) { if som...

The prefix ! operator returns the logical negation of its argument. That is, !true returns false, and !false returns true. print(!true) // prints "false" print(!false) // prints "true" func test(_ someBoolean: Bool) { if !someBoolean { print("someBoolean ...

NSArray *myColors = [NSArray arrayWithObjects: @"Red", @"Green", @"Blue", @"Yellow", nil]; NSLog (@"Number of elements in array = %lu", [myColors count]);

You can "overwrite" a parent element's language declaration by introducing any element apart from applet, base, basefont, br, frame, frameset, hr, iframe, meta, param, script (of HTML 4.0) with an own lang attribute: <p lang="en" title="An English paragraph"> ...