我有一个运行压力测试的AppleScript脚本。测试的一部分是打开、保存和关闭某些文件。不知何故，文件获得了一些禁止保存文件的“扩展属性”。这会导致压力测试失败。

如何删除扩展属性?

我在Mac OS X v10.8 (Mountain Lion)上安装了JDK。当我将其升级到Mac OS X v10.9 (Mavericks)并在终端中运行java -version时，它显示:

没有Java运行时，请求安装。

然后我手动在我的Mac上安装了JDK(1.7)。看起来安装工作正常。安装完成后，我打开终端并输入java -version。它还显示了同样的错误:

没有Java运行时，请求安装。

我该如何解决这个问题呢?

UPSERT操作在表中更新或插入一行，这取决于表中是否已经有与数据匹配的行:

if table t has a row exists that has key X:
    update t set mystuff... where mykey=X
else
    insert into t mystuff...

既然Oracle没有特定的UPSERT语句，那么最好的方法是什么呢?

我只是想知道谁知道Windows、Mac OS X和Linux是由哪些编程语言组成的，以及操作系统的每个部分都使用了哪些语言(例如:内核、插件架构、GUI组件等)。

我假设每种都有多种语言，显然我知道Linux内核是用C编写的。

我完全猜测Mac OS X包含大量Objective-C代码，因为它是苹果从NeXT派生的语言。

Windows，我听说包含C, c++和英特尔汇编。Linux或Mac OS是否包含任何汇编代码?

还有，是否有像Ruby, Python之类的脚本语言被操作系统开发者用来编写部分操作系统的脚本?操作系统的哪些部分是用每种语言编写的?

官方页面没有提到这种情况。但是许多用户只需要psql而不需要本地数据库(我在AWS上有它)。酿造没有psql。

当我在终端中运行brew时，我得到一个错误:

 /System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/lib/ruby/2.0.0/rubygems/core_ext/kernel_require.rb:55:in `require': cannot load such file -- utils/popen (LoadError)
from /System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/lib/ruby/2.0.0/rubygems/core_ext/kernel_require.rb:55:in `require'
from /usr/local/Library/Homebrew/utils.rb:6:in `<top (required)>'
from /System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/lib/ruby/2.0.0/rubygems/core_ext/kernel_require.rb:55:in `require'
from /System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/lib/ruby/2.0.0/rubygems/core_ext/kernel_require.rb:55:in `require'
from /usr/local/Library/Homebrew/global.rb:9:in `<top (required)>'
from /System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/lib/ruby/2.0.0/rubygems/core_ext/kernel_require.rb:55:in `require'
from /System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/lib/ruby/2.0.0/rubygems/core_ext/kernel_require.rb:55:in `require'
from /usr/local/Library/brew.rb:16:in `<main>'

这些是我的宝石设置:

- RUBYGEMS VERSION: 2.0.14
- RUBY VERSION: 2.0.0 (2014-02-24 patchlevel 451) [universal.x86_64-darwin13]
- INSTALLATION DIRECTORY: /Library/Ruby/Gems/2.0.0
- RUBY EXECUTABLE: /System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/bin/ruby
- EXECUTABLE DIRECTORY: /usr/bin
- RUBYGEMS PLATFORMS:
  - ruby
  - universal-darwin-13
- GEM PATHS:
  - /Library/Ruby/Gems/2.0.0
  - /Users/ronaldkwan/.gem/ruby/2.0.0
  - /System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/lib/ruby/gems/2.0.0
- GEM CONFIGURATION:
  - :update_sources => true
  - :verbose => true
  - :backtrace => false
  - :bulk_threshold => 1000

操作系统:Mac OS X 10.7.5 Python版本:2.7.5

我已经从https://pypi.python.org/pypi/setuptools用ez_setup.py安装了setuptools 1.0 然后我从https://pypi.python.org/pypi/pip/1.4.1下载pip.1.4.1 pkg。

在iTerm中运行(sudo) python setup.py install即可显示

running install
running bdist_egg running egg_info writing requirements to
pip.egg-info/requires.txt writing pip.egg-info/PKG-INFO writing
top-level names to pip.egg-info/top_level.txt writing dependency_links
to pip.egg-info/dependency_links.txt writing entry points to
pip.egg-info/entry_points.txt warning: manifest_maker: standard file
'setup.py' not found

reading manifest file 'pip.egg-info/SOURCES.txt' writing manifest file
'pip.egg-info/SOURCES.txt' installing library code to
build/bdist.macosx-10.6-intel/egg running install_lib warning:
install_lib: 'build/lib' does not exist -- no Python modules to
install

creating build/bdist.macosx-10.6-intel/egg creating
build/bdist.macosx-10.6-intel/egg/EGG-INFO copying
pip.egg-info/PKG-INFO -> build/bdist.macosx-10.6-intel/egg/EGG-INFO
copying pip.egg-info/SOURCES.txt ->
build/bdist.macosx-10.6-intel/egg/EGG-INFO copying
pip.egg-info/dependency_links.txt ->
build/bdist.macosx-10.6-intel/egg/EGG-INFO copying
pip.egg-info/entry_points.txt ->
build/bdist.macosx-10.6-intel/egg/EGG-INFO copying
pip.egg-info/not-zip-safe ->
build/bdist.macosx-10.6-intel/egg/EGG-INFO copying
pip.egg-info/requires.txt ->
build/bdist.macosx-10.6-intel/egg/EGG-INFO copying
pip.egg-info/top_level.txt ->
build/bdist.macosx-10.6-intel/egg/EGG-INFO creating
'dist/pip-1.4.1-py2.7.egg' and adding
'build/bdist.macosx-10.6-intel/egg' to it removing
'build/bdist.macosx-10.6-intel/egg' (and everything under it)
Processing pip-1.4.1-py2.7.egg removing
'/Users/dl/Library/Python/2.7/lib/python/site-packages/pip-1.4.1-py2.7.egg'
(and everything under it) creating
/Users/dl/Library/Python/2.7/lib/python/site-packages/pip-1.4.1-py2.7.egg
Extracting pip-1.4.1-py2.7.egg to
/Users/dl/Library/Python/2.7/lib/python/site-packages pip 1.4.1 is
already the active version in easy-install.pth Installing pip script
to /Users/dl/Library/Python/2.7/bin Installing pip-2.7 script to
/Users/dl/Library/Python/2.7/bin

Installed
/Users/dl/Library/Python/2.7/lib/python/site-packages/pip-1.4.1-py2.7.egg
Processing dependencies for pip==1.4.1 Finished processing
dependencies for pip==1.4.1

然后我输入pip install，错误信息是这样的

Traceback (most recent call last):   File
"/Library/Frameworks/Python.framework/Versions/2.7/bin/pip", line 9,
in <module>
load_entry_point('pip==1.4.1', 'console_scripts', 'pip')()   File "build/bdist.macosx-10.6-intel/egg/pkg_resources.py", line 357, in
load_entry_point   File
"build/bdist.macosx-10.6-intel/egg/pkg_resources.py", line 2394, in
load_entry_point   File
"build/bdist.macosx-10.6-intel/egg/pkg_resources.py", line 2108, in
load ImportError: No module named pip

谁以前遇到过同样的问题，能给我一些解决方法吗?

我正在学习表变量的更多细节。它说临时表总是在磁盘上，而表变量在内存中，也就是说，表变量的性能比临时表好，因为表变量比临时表使用更少的IO操作。

但是有时候，如果一个表变量中有太多记录不能包含在内存中，那么这个表变量就会像临时表一样被放到磁盘上。

但我不知道“太多记录”是什么意思。100000条记录吗?还是100万条记录?我如何知道我正在使用的表变量是在内存中还是在磁盘上?在SQL Server 2005中是否有任何函数或工具来测量表变量的规模，或者让我知道表变量何时从内存中放到磁盘上?

在C中使用printf时如何转义%符号?

printf("hello\%"); /* not like this */

我想为文本字段提供一个初始值，并重新绘制一个空值以清除文本。用Flutter的api实现这一点的最佳方法是什么?