为什么此Shell脚本仅对一个实例有效，而对另一个实例无效? [英] Why does this shell script work for one instance and not the other?

问题描述

我需要对以下代码进行一些解释，因为它们是相同的概念，但工作原理不同.因此，我正在尝试执行以下操作:

I'm in need of some explanation of the following code, because they are the same concepts but not working the same. So, I'm trying to do the following:

#!/bin/sh

ssh -T username@host << EOF

relative="$HOME/Documents"
command=$(find \$relative -name GitHub)
command2=$(echo \$relative)
echo "HERE: \$command"
echo "HERE: \$command2"

EOF

这是我得到的输出:

find: ‘$relative’: No such file or directory 
HERE:
HERE: /home/username/Documents

我尝试了以下操作:

"\$relative"
'\$relative'
"\${relative}"
"\$(relative)"

推荐答案

您大部分步骤都做对了，但是忘记了这里文档 $(..)中的命令替换构造..不这样做将使命令在本地外壳而不是远程主机中扩展.

You did the most parts right, but forgot to escape the command-substitution construct in the here-doc $(..). Not doing it will make the command expand in the local shell and not in the remote host.

在运行 find 命令时，转义的 \ $ relative 会将文字字符串传递给它不理解的 find 命令，即在本地计算机上发生以下情况

Also while running the find command an escaped \$relative will pass the literal string to the find command which it does not understand, i.e. the following happens on the local machine

find \$relative
#   ^^^^ since $relative won't expand, find throws an error

因此，您需要转义整个命令替换结构，以将整个here-doc扩展移动到远程主机中.

So you need to escape the whole command-substitution constructs, to move the whole here-doc expansion in the remote host.

ssh -T username@host << EOF
relative="\$HOME/Documents"
command=\$(find "\$relative" -name GitHub)
command2=\$(echo "\$relative")
echo "HERE: \$command"
echo "HERE: \$command2"
EOF

或者完全使用heredocs的替代形式，允许您不解释heredoc文本中的变量.只需将定界标识符引用为'EOF'

Or altogether use an alternate form of heredocs that allows you to not interpret variables in the heredoc text. Simply quote the delimiting identifier as 'EOF'

ssh -T username@host <<'EOF'
relative="$HOME/Documents"
command=$(find "$relative" -name GitHub)
command2=$(echo "$relative")
echo "HERE: $command"
echo "HERE: $command2"
EOF

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