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How to tell if a string is not defined in a Bash shell script
...guish whether VAR is set but empty or not set, you can use:
if [ -z "${VAR+xxx}" ]; then echo VAR is not set at all; fi
if [ -z "$VAR" ] && [ "${VAR+xxx}" = "xxx" ]; then echo VAR is set but empty; fi
You probably can combine the two tests on the second line into one with:
if [ -z "$VAR" -a...
Getting the exception value in Python
...
use str
try:
some_method()
except Exception as e:
s = str(e)
Also, most exception classes will have an args attribute. Often, args[0] will be an error message.
It should be noted that just using str will return an empty string if there's no error...
How do I compare two hashes?
...ws deep comparison of hashes and arrays in the hash.
The following is an example:
a = {a:{x:2, y:3, z:4}, b:{x:3, z:45}}
b = {a:{y:3}, b:{y:3, z:30}}
diff = HashDiff.diff(a, b)
diff.should == [['-', 'a.x', 2], ['-', 'a.z', 4], ['-', 'b.x', 3], ['~', 'b.z', 45, 30], ['+', 'b.y', 3]]
...
二维码的生成细节及原理 - 更多技术 - 清泛网 - 专注C/C++及内核技术
...下二维码一共有40个尺寸。官方叫版本Version。Version 1是21 x 21的矩阵，Version 2是 25 x 25的矩阵，Version 3是29的尺寸，每增加一个version，就会增加4的尺寸，公式是：(V-1)*4 + 21（V是版本号） 最高Version 40，(40-1)*4+21 = 177，所以最高是177...
How to terminate the script in JavaScript?
How can I exit the JavaScript script much like PHP's exit or die ? I know it's not the best programming practice but I need to.
...
What is a wrapper class?
...raction from the implementation of the underlying class or component; for example, wrapper classes that wrap COM components can manage the process of invoking the COM component without bothering the calling code with it. They can also simplify the use of the underlying object by reducing the number...
JSON.parse vs. eval()
...n.parse just parses JSON whereas eval would leave the door open to all JS expressions.
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Convert to binary and keep leading zeros in Python
...at Specification mini language. The # makes the format include the 0b prefix, and the 010 size formats the output to fit in 10 characters width, with 0 padding; 2 characters for the 0b prefix, the other 8 for the binary digits.
This is the most compact and direct option.
If you are putting the res...
How can I reliably determine the type of a variable that is declared using var at design time?
...ween keystrokes.
When the IDE needs to work out the type of a particular expression inside a method body -- say you've typed "foo." and we need to figure out what are the members of foo -- we do the same thing; we skip as much work as we reasonably can.
We start with a pass which analyzes only th...
How to truncate string using SQL server
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If col is exactly 15 in length it will get the entire string when doing left(col,15) and then put '...' on the end. Surely a better solution is checking 'when len(col) > 15'.
– Murphybro2
Dec 6 ...