当通过ssh传递时，为什么带引号的空格命令不起作用？ [英] Why doesn't a command with quoted whitespace work when passed over ssh?

问题描述

我正在构建此项目，在该项目中必须使用ssh执行UNIX命令。这是我的问题：在UNIX shell中执行以下命令时，

I am building this project in which I have to execute UNIX commands using ssh. Here is my question : When I execute the following command in a UNIX shell,

echo "Hello           World"

它产生输出：

Hello           World

参数之间有5个空格用双引号引起来。我也想通过ssh达到相同的效果。我试图使用反斜杠转义双引号，如下所示：

With 5 spaces in between as the arguments were given within double quotes. I want to achieve the same effects with ssh as well. I am trying to escape the double quotes using backslash as follows :

ssh localhost echo \"Hello           World\"

因为我不希望bash处理报价。但这只会产生

as I do not want bash to process the quotes. But it just produces

Hello           World

Hello之后只有一个空格
为什么？

There is only one space after "Hello" Why is that?

推荐答案

ssh 执行一个命令，该命令是通过调用远程shell给出的，该脚本由脚本组成，该脚本由完整的本地参数集以及它们之间的空格组成。

ssh executes a command it's given by invoking a remote shell with a script composed of the full set of local arguments concatenated together with whitespace between them.

如果您运行：

# This has only syntactic quotes -- none of the quotes are literal.
ssh somehost echo "Hello   World"

..然后将此参数列表传递给 ssh （使用C语法，不包括主机名和ssh命令本身）为 { echo， Hello World，NULL} 。

..then this list of arguments passed to ssh (in C syntax, excluding the hostname and the ssh command itself) is { "echo", "Hello World", NULL }.

连接成一个字符串，然后变成 echo Hello World 。

Concatenated together into a string, this then becomes "echo Hello World".

因此，远程shell运行 echo Hello World ，它没有语法引号。

Thus, the remote shell runs echo Hello World, which has no syntactic quotes.

如果您运行：

ssh somehost echo \"Hello   World\"

...然后是命令列表（再次使用C语法）是 { echo， \ Hello， World\，NULL} ：引号是文字，但空格已由本地外壳程序删除（在运行SSH之前）在分词过程中。

...then the list of commands (again, in C syntax) is { "echo", "\"Hello", "World\"", NULL }: The quotes are literal, but the spaces were removed by the local shell (before SSH was run) during the word-splitting process.

连接到字符串中后，它会成为 echo Hello World 。因此，您得到的是报价，但是却失去了空格。

Concatenated into a string, this becomes echo "Hello World". Thus, you get quotes, but lose your spaces.

相反，这是可行的（但不是最佳实践） ）示例，请考虑：

By contrast, as a working (but not particularly best-practice) example, consider:

ssh somehost echo \"Hello"   "World\"

在这里，您要传递 ssh 两个参数： \ 的开头和结尾是第一个shell的文字（没有语法含义，因此 Hello 是第一个shell未引用）；但是仅在空白周围的 是语法上的，并告诉Shell保留该空白（因此引用了 space ）调用 ssh 时。因此，您将得到 { echo， \ Hello World\，NULL} ，它连接到字符串 echo Hello世界。

Here, you're passing ssh two arguments: The \"s at the beginning and end are literal to the first shell (having no syntactical meaning, so the word Hello is to that first shell unquoted); but the "s just surrounding the whitespace is syntactical, and tells the shell to preserve that whitespace (so the spaces are quoted) when invoking ssh. Thus, you get { "echo", "\"Hello World\"", NULL }, which concatenates to the string echo "Hello World".

最佳做法是通过仅传递单个字符串来避免此行为

The best practice is to avoid this behavior by passing only a single string to ssh containing the entire script you want to run.

# This works
ssh somehost 'echo "Hello   World"'

...如果要以编程方式生成该字符串，则可以这样操作（如果您知道您的远程shell是bash －即使bash-in- / bin / sh 模式也是安全的）：

...if you want to generate that string programatically, you can do so as such (if you know that your remote shell is bash -- even bash-in-/bin/sh mode is safe):

remote_command=( echo "Hello   World" )
printf -v remote_command_q '%q ' "${remote_command[@]}"
ssh somehost "$remote_command_q"

要使用任何符合POSIX的远程shell安全地执行此操作，请参见< a href = https://stackoverflow.com/questions/45308395/how-to-have-simple-and-double-quotes-in-a-scripted-ssh-command>如何在脚本化的ssh命令中使用单引号和双引号

To do that safely with any POSIX-compliant remote shell, see the Python-assisted answer in How to have simple and double quotes in a scripted ssh command

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