variables

问题 This question already has answers here : Why does shell ignore quotes in arguments passed to it through variables? [duplicate] (3 answers) Closed 3 years ago . If i use this command in pipeline, it's working very well; pipeline ... | grep -P '^[^\s]*\s3\s' But if I want to set grep into variable like: var="grep -P '^[^\s]*\s3\s'" And if I put variable in pipeline; pipeline ... | $var nothing happens, like there isn't any matches. Any help what am I doing wrong? 回答1: The robust way to store a

问题 My code: function Check($Variable, $DefaultValue) { if(isset($Variable) && $Variable != "" && $Variable != NULL) { return $Variable; } else { return $DefaultValue; } } $a = Check(@$foo, false); $b = Check(@$bar, "Hello"); //$a now equals false because $foo was not set. //$b now equals "Hello" because $bar was not set. When a variable doesn't exist and is passed to the function (suppressing the error) what is actually passed? Is there any undefined behaviour that this function could exhibit?

问题 As per the title. I have the following code which creates a binary search tree, but if I want it created and changed dynamically with user input, how would I do that if I can't change the value of a variable in haskell?!? find :: (Ord a) => Node a -> a -> Bool find (Node val left right) s | s == val = True | s < val = find left s | s > val = find right s find Empty s = False data Node a = Node a (Node a) (Node a) | Empty myTree = Node "m" (Node "a" Empty Empty) (Node "z" Empty Empty) Thanks

问题 somevar := apple export somevar update := $(shell echo "v=$$somevar") all: @echo $(update) I was hoping to apple as output of command, however it's empty, which makes me think export and := variable expansion taking place on different phases. how to overcome this? 回答1: The problem is that export exports the variable to the subshells used by the commands; it is not available for expansion in other assignments. So don't try to get it from the environment outside a rule. somevar := apple export

问题 I'm trying to base64 encode an image in a shell script and put it into variable: test="$(printf DSC_0251.JPG | base64)" echo $test RFNDXzAyNTEuSlBH I've also tried something like this: test=\`echo -ne DSC_0251.JPG | base64\` but still with no success. I want to do something like this: curl -v -X POST -d '{"image":$IMAGE_BASE64,"location":$LOCATION,"time_created":$TIMECREATED}' -H 'Content-type: text/plain; charset=UTF8' http://192.168.1.1/upload I found this http://www.zzzxo.com/q/answers

问题 I'm trying to base64 encode an image in a shell script and put it into variable: test="$(printf DSC_0251.JPG | base64)" echo $test RFNDXzAyNTEuSlBH I've also tried something like this: test=\`echo -ne DSC_0251.JPG | base64\` but still with no success. I want to do something like this: curl -v -X POST -d '{"image":$IMAGE_BASE64,"location":$LOCATION,"time_created":$TIMECREATED}' -H 'Content-type: text/plain; charset=UTF8' http://192.168.1.1/upload I found this http://www.zzzxo.com/q/answers

问题 I'm practicing some work from my java book and I'm having an issue with getting a method to use a variable for a calculation. Please note that this is a work in progress and I'm only trying to get it to use the circleArea method to calculate the area of a circle at the moment. Here is the necessary code: public class Geometry { public static void printMenu() { System.out.println("This is a geometry calculator\nChoose what you would like to calculate" + "\n1. Find the area of a circle\n2. Find

问题 How do i detect or capture change of value of a global variable in python variable = 10 print(variable) variable = 20 # Detect changes to the value using a signal to trigger a function UPDATE AST docs - GOOD INTRO https://greentreesnakes.readthedocs.io/en/latest/ 回答1: To my knowledge, it is not possible to generically capture the assignment of a global symbol in Python (At least in CPython where globals are stored in a dict in the module object, both are C types that cannot be monkey patched)

问题 i'm trying to calculate the 95th percentile for multiple water quality values grouped by watershed. for example... Watershed WQ 50500101 62.370661 50500101 65.505046 50500101 58.741477 50500105 71.220034 50500105 57.917249 i reviewed this question posted - Percentile for Each Observation w/r/t Grouping Variable. it seems very close to what i want to do but it's for EACH observation. i need it for each grouping variable. so ideally, Watershed WQ - 95th 50500101 x 50500105 y thanks 回答1: This

问题 A layman's question on the definition and use of variables: I need to make a Java GUI that gets user's input and stores it within a text file. However this writing has to be done inside an Actionlistener class (ie, user is clicking the button and text file is created and stored). This means that I have to define a variable in one class (public class) and use it in another (the one that defines the Actionlistener). How can I do this? Are global variables the only way? In my code I first define