blocks|key|1380301|text|您可以使用反引号：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1380302|`ls`|code-block|syntax|javascript|1380303|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

You use backticks:

<pre><code>`ls`
</code></pre>

blocks|key|1595429|text|另一种方式是：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1595430|f+=+open("%7Cls")
foo+=+f.read()|code-block|syntax|javascript|1595431|请注意，这是open中"ls“之前的”管道“字符。这也可用于将数据输入到程序的标准输入以及读取其标准输出。|1595432|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|K|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|L|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|M|8|@]|9|@]|A|$]]|$1|I|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|J|$]]

Another way is:

<pre><code>f = open("|ls")
foo = f.read()
</code></pre>

Note that's the "pipe" character before "ls" in open. This can also be used to feed data into the programs standard input as well as reading its standard output.

blocks|key|1380400|text|我想对chaos's+answer做一点扩展和澄清。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|1380401|如果您用反引号将命令括起来，那么您根本不需要(显式地)调用system()。反引号执行命令并以字符串的形式返回输出。然后，您可以将该值赋给变量，如下所示：|1380402|output+=+`ls`
p+output|code-block|syntax|javascript|1380403|或|1380404|printf+output+#+escapes+newline+chars|1380405|entityMap|0|LINK|mutability|MUTABLE|url|https://stackoverflow.com/a/690174/56763^0|3|E|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|W|8|@]|9|@$A|X|B|Y|1|Z]]|C|$]]|$1|D|3|E|5|6|7|10|8|@]|9|@]|C|$]]|$1|F|3|G|5|H|7|11|8|@]|9|@]|C|$I|J]]|$1|K|3|L|5|6|7|12|8|@]|9|@]|C|$]]|$1|M|3|N|5|H|7|13|8|@]|9|@]|C|$I|J]]|$1|O|3|-4|5|6|7|14|8|@]|9|@]|C|$]]]|P|$Q|$5|R|S|T|C|$U|V]]]]

I'd like to expand &amp; clarify <a href="https://stackoverflow.com/a/690174/56763">chaos's answer</a> a bit.

If you surround your command with backticks, then you don't need to (explicitly) call system() at all. The backticks execute the command and return the output as a string. You can then assign the value to a variable like so:

<pre><code>output = `ls`
p output
</code></pre>

or

<pre><code>printf output # escapes newline chars
</code></pre>

blocks|key|1380444|text|我发现如果你需要返回值，下面的代码会很有用：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1380445|result+=+%25x[ls]
puts+result|code-block|syntax|javascript|1380446|我特别想列出我机器上所有Java进程的pids，并使用以下代码：|1380447|ids+=+%25x[ps+ax+%7C+grep+java+%7C+awk+'{+print+$1+}'+%7C+xargs]|1380448|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|N|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|O|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|K|3|-4|5|6|7|Q|8|@]|9|@]|A|$]]]|L|$]]

I found that the following is useful if you need the return value:

<pre><code>result = %x[ls]
puts result
</code></pre>

I specifically wanted to list the pids of all the Java processes on my machine, and used this:

<pre><code>ids = %x[ps ax | grep java | awk '{ print $1 }' | xargs]
</code></pre>

blocks|key|1380486|text|作为直接系统(...)替换您可以使用Open3.popen3(...)|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1380487|进一步讨论：http://tech.natemurray.com/2007/03/ruby-shell-commands.html|offset|length|1380488|entityMap|0|LINK|mutability|MUTABLE|url|http://tech.natemurray.com/2007/03/ruby-shell-commands.html^0|0|6|1N|0|0^^$0|@$1|2|3|4|5|6|7|N|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|O|8|@]|9|@$D|P|E|Q|1|R]]|A|$]]|$1|F|3|-4|5|6|7|S|8|@]|9|@]|A|$]]]|G|$H|$5|I|J|K|A|$L|M]]]]

As a direct system(...) replacement you may use Open3.popen3(...)

Further discussion:
<a href="http://tech.natemurray.com/2007/03/ruby-shell-commands.html" rel="noreferrer">http://tech.natemurray.com/2007/03/ruby-shell-commands.html</a>

blocks|key|1380537|text|仅供记录，如果您想要(输出和操作结果)，您可以这样做：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1380538|output=`ls+no_existing_file`+;++result=$?.success?|code-block|syntax|javascript|1380539|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

Just for the record, if you want both (output and operation result) you can do:

<pre><code>output=`ls no_existing_file` ; result=$?.success?
</code></pre>

blocks|key|1380566|text|您可以使用system()或%25x[]，这取决于您需要的结果类型。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1380567|如果找到并成功运行命令，则system()返回true，否则返回false。|1380568|>>+s+=+system+'uptime'
10:56++up+3+days,+23:10,+2+users,+load+averages:+0.17+0.17+0.14
=>+true
>>+s.class
=>+TrueClass
>>+$?.class
=>+Process::Status|code-block|syntax|javascript|1380569|%25x..另一方面，将命令的结果保存为字符串：|1380570|>>+result+=+%25x[uptime]
=>+"13:16++up+4+days,++1:30,+2+users,+load+averages:+0.39+0.29+0.23\n"
>>+p+result+
"13:16++up+4+days,++1:30,+2+users,+load+averages:+0.39+0.29+0.23\n"
>>+result.class
=>+String|1380571|此blog+post+by+Jay+Fields详细说明了使用system、exec和%25x之间的区别。。|offset|length|1380572|entityMap|0|LINK|mutability|MUTABLE|url|http://blog.jayfields.com/2006/06/ruby-kernel-system-exec-and-x.html^0|0|0|0|0|0|1|N|0|0^^$0|@$1|2|3|4|5|6|7|Y|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|Z|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|10|8|@]|9|@]|A|$G|H]]|$1|I|3|J|5|6|7|11|8|@]|9|@]|A|$]]|$1|K|3|L|5|F|7|12|8|@]|9|@]|A|$G|H]]|$1|M|3|N|5|6|7|13|8|@]|9|@$O|14|P|15|1|16]]|A|$]]|$1|Q|3|-4|5|6|7|17|8|@]|9|@]|A|$]]]|R|$S|$5|T|U|V|A|$W|X]]]]

You can use system() or %x[] depending what kind of result you need.

system() returning true if the command was found and ran successfully, false otherwise.

<pre><code>&gt;&gt; s = system 'uptime'
10:56 up 3 days, 23:10, 2 users, load averages: 0.17 0.17 0.14
=&gt; true
&gt;&gt; s.class
=&gt; TrueClass
&gt;&gt; $?.class
=&gt; Process::Status
</code></pre>

%x[..] on the other hand saves the results of the command as a string:

<pre><code>&gt;&gt; result = %x[uptime]
=&gt; "13:16 up 4 days, 1:30, 2 users, load averages: 0.39 0.29 0.23\n"
&gt;&gt; p result 
"13:16 up 4 days, 1:30, 2 users, load averages: 0.39 0.29 0.23\n"
&gt;&gt; result.class
=&gt; String
</code></pre>

Th <a href="http://blog.jayfields.com/2006/06/ruby-kernel-system-exec-and-x.html" rel="noreferrer">blog post by Jay Fields</a> explains in detail the differences between using system, exec and %x[..] .

blocks|key|1595652|text|请注意，将包含用户提供的值的字符串传递给system、%25x[]等的所有解决方案都是不安全的！不安全实际上意味着:用户可能会触发代码在上下文中运行，并具有程序的所有权限。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1595653|据我所知，只有system和Open3.popen3在Ruby1.8中提供了一个安全/转义的变体。在Ruby1.9中，IO::popen也接受数组。|1595654|只需将每个选项和参数作为数组传递给其中一个调用。|1595655|如果您不仅需要退出状态，而且还需要结果，那么您可能希望使用Open3.popen3|1595656|require+'open3'
stdin,+stdout,+stderr,+wait_thr+=+Open3.popen3('usermod',+'-p',+@options['shadow'],+@options['username'])
stdout.gets(nil)
stdout.close
stderr.gets(nil)
stderr.close
exit_code+=+wait_thr.value|code-block|syntax|javascript|1595657|请注意，块形式将自动关闭stdin、stdout和stderr-否则它们必须为closed+explicitly。|1595658|更多信息请点击此处：Forming+sanitary+shell+commands+or+system+calls+in+Ruby|1595659|entityMap|0|LINK|mutability|MUTABLE|url|http://www.ruby-doc.org/stdlib-2.0/libdoc/open3/rdoc/Open3.html#method-c-popen3|1|https://stackoverflow.com/questions/4650636/forming-sanitary-shell-commands-or-system-calls-in-ruby^0|K|6|R|4|0|7|6|E|C|1N|9|0|0|T|C|0|0|13|H|0|0|A|1J|1|0^^$0|@$1|2|3|4|5|6|7|14|8|@$9|15|A|16|B|C]|$9|17|A|18|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|19|8|@$9|1A|A|1B|B|C]|$9|1C|A|1D|B|C]|$9|1E|A|1F|B|C]]|D|@]|E|$]]|$1|H|3|I|5|6|7|1G|8|@]|D|@]|E|$]]|$1|J|3|K|5|6|7|1H|8|@$9|1I|A|1J|B|C]]|D|@]|E|$]]|$1|L|3|M|5|N|7|1K|8|@]|D|@]|E|$O|P]]|$1|Q|3|R|5|6|7|1L|8|@]|D|@$9|1M|A|1N|1|1O]]|E|$]]|$1|S|3|T|5|6|7|1P|8|@]|D|@$9|1Q|A|1R|1|1S]]|E|$]]|$1|U|3|-4|5|6|7|1T|8|@]|D|@]|E|$]]]|V|$W|$5|X|Y|Z|E|$10|11]]|12|$5|X|Y|Z|E|$10|13]]]]

Be aware that all the solutions where you pass a string containing user provided values to <code>system</code>, <code>%x[]</code> etc. are unsafe! Unsafe actually means: the user may trigger code to run in the context and with all permissions of the program.

As far as I can say only <code>system</code> and <code>Open3.popen3</code> do provide a secure/escaping variant in Ruby 1.8. In Ruby 1.9 <code>IO::popen</code> also accepts an array.

Simply pass every option and argument as an array to one of these calls.

If you need not just the exit status but also the result you probably want to use <code>Open3.popen3</code>:

<pre><code>require 'open3'
stdin, stdout, stderr, wait_thr = Open3.popen3('usermod', '-p', @options['shadow'], @options['username'])
stdout.gets(nil)
stdout.close
stderr.gets(nil)
stderr.close
exit_code = wait_thr.value
</code></pre>

Note that the block form will auto-close stdin, stdout and stderr- otherwise they'd have to be <a href="http://www.ruby-doc.org/stdlib-2.0/libdoc/open3/rdoc/Open3.html#method-c-popen3" rel="noreferrer">closed explicitly</a>.

More information here: <a href="https://stackoverflow.com/questions/4650636/forming-sanitary-shell-commands-or-system-calls-in-ruby">Forming sanitary shell commands or system calls in Ruby</a>

blocks|key|1595685|text|如果你需要对参数进行转义，在Ruby1.9中，IO.popen也接受数组：|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|1595686|p+IO.popen(["echo",+"it's+escaped"]).read|code-block|syntax|javascript|1595687|在早期版本中，您可以使用Open3.popen3|1595688|require+"open3"

Open3.popen3("echo",+"it's+escaped")+{+%7Ci,+o%7C+p+o.read+}|1595689|如果您还需要传递stdin，这应该在1.9和1.8中都有效：|1595690|out+=+IO.popen("xxd+-p",+"r%2B")+{+%7Cio%7C
++++io.print+"xyz"
++++io.close_write
++++io.read.chomp
}
p+out+#+"78797a"|1595691|entityMap|0|LINK|mutability|MUTABLE|url|http://www.ruby-doc.org/core-1.9.3/IO.html#method-c-popen|1|http://www.ruby-doc.org/stdlib-1.9.3/libdoc/open3/rdoc/Open3.html#method-c-popen3^0|N|8|0|0|0|C|C|1|0|0|0|0^^$0|@$1|2|3|4|5|6|7|10|8|@]|9|@$A|11|B|12|1|13]]|C|$]]|$1|D|3|E|5|F|7|14|8|@]|9|@]|C|$G|H]]|$1|I|3|J|5|6|7|15|8|@]|9|@$A|16|B|17|1|18]]|C|$]]|$1|K|3|L|5|F|7|19|8|@]|9|@]|C|$G|H]]|$1|M|3|N|5|6|7|1A|8|@]|9|@]|C|$]]|$1|O|3|P|5|F|7|1B|8|@]|9|@]|C|$G|H]]|$1|Q|3|-4|5|6|7|1C|8|@]|9|@]|C|$]]]|R|$S|$5|T|U|V|C|$W|X]]|Y|$5|T|U|V|C|$W|Z]]]]

If you need to escape the arguments, in Ruby 1.9 <a href="http://www.ruby-doc.org/core-1.9.3/IO.html#method-c-popen">IO.popen</a> also accepts an array:

<pre><code>p IO.popen(["echo", "it's escaped"]).read
</code></pre>

In earlier versions you can use <a href="http://www.ruby-doc.org/stdlib-1.9.3/libdoc/open3/rdoc/Open3.html#method-c-popen3">Open3.popen3</a>:

<pre><code>require "open3"

Open3.popen3("echo", "it's escaped") { |i, o| p o.read }
</code></pre>

If you also need to pass stdin, this should work in both 1.9 and 1.8:

<pre><code>out = IO.popen("xxd -p", "r+") { |io|
 io.print "xyz"
 io.close_write
 io.read.chomp
}
p out # "78797a"
</code></pre>

blocks|key|1380660|text|虽然使用反引号或popen通常是你真正想要的，但它实际上并没有回答所提出的问题。捕获system输出可能有合理的理由(可能是为了自动化测试)。我在谷歌上搜索了一下turned+up+an+answer，我想我应该把它贴在这里，以便于其他人受益。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1380661|因为我需要这个来测试，所以我的示例使用一个块设置来捕获标准输出，因为实际的system调用隐藏在被测试的代码中：|1380662|require+'tempfile'

def+capture_stdout
++stdout+=+$stdout.dup
++Tempfile.open+'stdout-redirect'+do+%7Ctemp%7C
++++$stdout.reopen+temp.path,+'w%2B'
++++yield+if+block_given?
++++$stdout.reopen+stdout
++++temp.read
++end
end|code-block|syntax|javascript|1380663|此方法使用tempfile存储实际数据来捕获给定块中的任何输出。示例用法：|1380664|captured_content+=+capture_stdout+do
++system+'echo+foo'
end
puts+captured_content|1380665|您可以用内部调用system的任何内容替换system调用。如果需要，您还可以使用类似的方法来捕获stderr。|1380666|entityMap|0|LINK|mutability|MUTABLE|url|http://www.velocityreviews.com/forums/t812652-redirect-stdout-for-kernel-system.html^0|16|6|29|J|0|0|11|6|0|0|0|0|8|6|L|6|1D|6|0^^$0|@$1|2|3|4|5|6|7|10|8|@$9|11|A|12|B|C]]|D|@$9|13|A|14|1|15]]|E|$]]|$1|F|3|G|5|6|7|16|8|@$9|17|A|18|B|C]]|D|@]|E|$]]|$1|H|3|I|5|J|7|19|8|@]|D|@]|E|$K|L]]|$1|M|3|N|5|6|7|1A|8|@]|D|@]|E|$]]|$1|O|3|P|5|J|7|1B|8|@]|D|@]|E|$K|L]]|$1|Q|3|R|5|6|7|1C|8|@$9|1D|A|1E|B|C]|$9|1F|A|1G|B|C]|$9|1H|A|1I|B|C]]|D|@]|E|$]]|$1|S|3|-4|5|6|7|1J|8|@]|D|@]|E|$]]]|T|$U|$5|V|W|X|E|$Y|Z]]]]

While using backticks or popen is often what you really want, it doesn't actually answer the question asked. There may be valid reasons for capturing <code>system</code> output (maybe for automated testing). A little Googling <a href="http://www.velocityreviews.com/forums/t812652-redirect-stdout-for-kernel-system.html" rel="noreferrer">turned up an answer</a> I thought I would post here for the benefit of others. 

Since I needed this for testing my example uses a block setup to capture the standard output since the actual <code>system</code> call is buried in the code being tested:

<pre><code>require 'tempfile'

def capture_stdout
 stdout = $stdout.dup
 Tempfile.open 'stdout-redirect' do |temp|
 $stdout.reopen temp.path, 'w+'
 yield if block_given?
 $stdout.reopen stdout
 temp.read
 end
end
</code></pre>

This method captures any output in the given block using a tempfile to store the actual data. Example usage:

<pre><code>captured_content = capture_stdout do
 system 'echo foo'
end
puts captured_content
</code></pre>

You can replace the <code>system</code> call with anything that internally calls <code>system</code>. You could also use a similar method to capture <code>stderr</code> if you wanted.

blocks|key|1380721|text|如果希望使用Kernel#system将输出重定向到文件，可以像这样修改描述符：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1380722|以附加模式将stdout和stderr重定向到文件(/tmp/log)：|1380723|system('ls+-al',+:out+=>+['/tmp/log',+'a'],+:err+=>+['/tmp/log',+'a'])|1380724|对于长时间运行的命令，这将实时存储输出。您还可以使用IO.pipe存储输出，并从Kernel#system重定向它。|1380725|entityMap^0|6|D|0|0|0|1Y|0|0^^$0|@$1|2|3|4|5|6|7|N|8|@$9|O|A|P|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|Q|8|@]|D|@]|E|$]]|$1|H|3|I|5|6|7|R|8|@$9|S|A|T|B|C]]|D|@]|E|$]]|$1|J|3|K|5|6|7|U|8|@]|D|@]|E|$]]|$1|L|3|-4|5|6|7|V|8|@]|D|@]|E|$]]]|M|$]]

If you want the output redirected to a file using <code>Kernel#system</code>, you can do modify descriptors like this:

redirect stdout and stderr to a file(/tmp/log) in append mode:

<code>
system('ls -al', :out =&gt; ['/tmp/log', 'a'], :err =&gt; ['/tmp/log', 'a'])
</code>

For a long running command, this will store the output in real time. You can also, store the output using a IO.pipe and redirect it from Kernel#system.

blocks|key|1380768|text|作为Simon+Hürlimann+already+explained，Open3比反引号等更安全。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|1380769|require+'open3'
output+=+Open3.popen3("ls")+{+%7Cstdin,+stdout,+stderr,+wait_thr%7C+stdout.read+}|code-block|syntax|javascript|1380770|请注意，块形式将自动关闭stdin、stdout和stderr-否则它们必须为closed+explicitly。|1380771|entityMap|0|LINK|mutability|MUTABLE|url|https://stackoverflow.com/a/5970819/165673|1|http://www.ruby-doc.org/stdlib-2.0/libdoc/open3/rdoc/Open3.html#method-c-popen3|2^0|2|X|0|10|5|1|0|0|13|H|2|0^^$0|@$1|2|3|4|5|6|7|V|8|@]|9|@$A|W|B|X|1|Y]|$A|Z|B|10|1|11]]|C|$]]|$1|D|3|E|5|F|7|12|8|@]|9|@]|C|$G|H]]|$1|I|3|J|5|6|7|13|8|@]|9|@$A|14|B|15|1|16]]|C|$]]|$1|K|3|-4|5|6|7|17|8|@]|9|@]|C|$]]]|L|$M|$5|N|O|P|C|$Q|R]]|S|$5|N|O|P|C|$Q|T]]|U|$5|N|O|P|C|$Q|T]]]]

As <a href="https://stackoverflow.com/a/5970819/165673">Simon Hürlimann already explained</a>, <a href="http://www.ruby-doc.org/stdlib-2.0/libdoc/open3/rdoc/Open3.html#method-c-popen3" rel="noreferrer">Open3</a> is safer than backticks etc. 

<pre><code>require 'open3'
output = Open3.popen3("ls") { |stdin, stdout, stderr, wait_thr| stdout.read }
</code></pre>

Note that the block form will auto-close stdin, stdout and stderr- otherwise they'd have to be <a href="http://www.ruby-doc.org/stdlib-2.0/libdoc/open3/rdoc/Open3.html#method-c-popen3" rel="noreferrer">closed explicitly</a>.

blocks|key|1380779|text|puts+`date`
puts+$?


Mon+Mar++7+19:01:15+PST+2016
pid+13093+exit+0|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|1380780|unstyled|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|G|8|@]|9|@]|A|$B|C]]|$1|D|3|-4|5|E|7|H|8|@]|9|@]|A|$]]]|F|$]]

If I call a command using <a href="http://ruby-doc.org/core-2.2.0/Kernel.html#method-i-system" rel="noreferrer">Kernel#system</a> in Ruby, how do I get its output?

<pre><code>system("ls")
</code></pre>

Getting output of system() calls in Ruby

Ruby语言

Kernel

Java

如果我在Ruby语言中使用调用一个命令，我如何获得它的输出？system("ls")

问在Ruby中获取system()调用的输出
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