unset | 易学教程

Unset readonly variable in bash

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how to unset readonly variable in Bash? $ readonly PI=3.14 $ unset PI bash: PI: readonly variable or is it not possible? anishsane Actually, you can unset a readonly variable . but I must warn that this is a hacky method. Adding this answer, only as information, not as recommendation. Use at your own risk. Tested on ubuntu 13.04, bash 4.2.45. This method involves knowing a bit of bash source code & it's inherited from this answer. $ readonly PI=3.14 $ unset PI -bash: unset: PI: cannot unset: readonly variable $ cat << EOF| sudo gdb attach $$ call unbind_variable("PI") detach EOF $ echo $PI $ I

How do I delete an exported environment variable?

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问题 Before installing gnuplot, I set the environment variable GNUPLOT_DRIVER_DIR = /home/gnuplot/build/src . During the installation, something went wrong. I want to remove the GNUPLOT_DRIVER_DIR environment variable. How can I achieve it? 回答1: unset is the command you're looking for. unset GNUPLOT_DRIVER_DIR 回答2: Walkthrough of creating and deleting an environment variable in bash: Test if the DUALCASE variable exists: el@apollo:~$ env | grep DUALCASE el@apollo:~$ It does not, so create the

Unsetting array values in a foreach loop [duplicate]

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问题 This question already has an answer here: How do you remove an array element in a foreach loop? 8 answers I have a foreach loop set up to go through my array, check for a certain link, and if it finds it removes that link from the array. My code: foreach($images as $image) { if($image == \'http://i27.tinypic.com/29yk345.gif\' || $image == \'http://img3.abload.de/img/10nx2340fhco.gif\' || $image == \'http://i42.tinypic.com/9pp2456x.gif\') { unset($images[$image]); } } But it doesn\'t remove

How to delete object from array inside foreach loop?

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问题 I iterate through an array of objects and want to delete one of the objects based on it\'s \'id\' property, but my code doesn\'t work. foreach($array as $element) { foreach($element as $key => $value) { if($key == \'id\' && $value == \'searched_value\'){ //delete this particular object from the $array unset($element);//this doesn\'t work unset($array,$element);//neither does this } } } Any suggestions. Thanks. 回答1: foreach($array as $elementKey => $element) { foreach($element as $valueKey =>

How to remove a key from a Python dictionary?

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问题 When deleting a key from a dictionary, I use: if \'key\' in myDict: del myDict[\'key\'] Is there a one line way of doing this? 回答1: To delete a key regardless of whether it is in the dictionary, use the two-argument form of dict.pop(): my_dict.pop('key', None) This will return my_dict[key] if key exists in the dictionary, and None otherwise. If the second parameter is not specified (ie. my_dict.pop('key') ) and key does not exist, a KeyError is raised. To delete a key that is guaranteed to

Deleting an element from an array in PHP

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问题 Is there an easy way to delete an element from an array using PHP, such that foreach ($array) no longer includes that element? I thought that setting it to null would do it, but apparently it does not work. 回答1: There are different ways to delete an array element, where some are more useful for some specific tasks than others. Delete one array element If you want to delete just one array element you can use \unset() or alternatively \array_splice(). Also if you have the value and don't know