大约有 16,000 项符合查询结果（耗时：0.0180秒） [XML]
What is the difference between ${var}, “$var”, and “${var}” in the Bash shell?
...pecial characters.
I'd love to hear the detailed explanation. My testing confirms this, and I'm now quoting my variables for all string tests, to avoid having -z and -n return the same result.
$ unset a
$ if [ -z $a ]; then echo unset; else echo set; fi
unset
$ if [ -n $a ]; then echo set; else e...
How do I install pip on macOS or OS X?
I spent most of the day yesterday searching for a clear answer for installing pip (package manager for Python). I can't find a good solution.
...
How do I edit /etc/sudoers from a script?
...make your edits to a temporary file, then use visudo -c -f sudoers.temp to confirm that the changes are valid and then copy it over the top of /etc/sudoers
#!/bin/sh
if [ -f "/etc/sudoers.tmp" ]; then
exit 1
fi
touch /etc/sudoers.tmp
edit_sudoers /tmp/sudoers.new
visudo -c -f /tmp/sudoers.new
i...
How accurate is python's time.sleep()?
...
The accuracy of the time.sleep function depends on your underlying OS's sleep accuracy. For non-realtime OS's like a stock Windows the smallest interval you can sleep for is about 10-13ms. I have seen accurate sleeps within several milliseconds of that time when above the minimum 10-13ms.
...
Can you do a partial checkout with Subversion?
...directories under trunk/ with lots of files in each and only needed 3 of those directories, would it be possible to do a Subversion checkout with only those 3 directories under trunk?
...
When to use the brace-enclosed initializer?
... Hmm, you're right - I was testing with GCC 4.5 earlier which seemed to confirm what I was saying, but GCC 4.6 does agree with you. And I did miss the fact that you were talking about in-class initialization. My apologies.
– interjay
Apr 2 '12 at 18:09
...
How do I set up a simple delegate to communicate between two view controllers?
...(MyDatatwo*) dataTwo;
@end
Import MyFirstControllerDelegate.h file and confirm your FirstController with protocol MyFirstControllerDelegate
#import "MyFirstControllerDelegate.h"
@interface FirstController : UIViewController<MyFirstControllerDelegate>
{
}
@end
In the implementation f...
Is it possible to get CMake to build both a static and shared version of the same library?
...
@gnac I cannot confirm this. In my case, the set_property only worked when I used objlib and not when using ${objlib}. So maybe this answer could be corrected?
– josch
May 12 '17 at 9:24
...
Python exit commands - why so many and when should each be used?
...xecution. The choices I've found are: quit() , exit() , sys.exit() , os._exit()
4 Answers
...
Redirecting stdout to “nothing” in python
...
Cross-platform:
import os
import sys
f = open(os.devnull, 'w')
sys.stdout = f
On Windows:
f = open('nul', 'w')
sys.stdout = f
On Linux:
f = open('/dev/null', 'w')
sys.stdout = f
...