3.5.4 命令替换（Command Substitution）

作用

将一个命令的输出（output）替换为命令本身

一般形式

$(command)或`command`

注意点

• bash在subshell中执行command然后替换
• 执行command产生的输出中的newline（“\n”）将被删除
• 可嵌套，若用反引号嵌套，内层反引号用“\”转义

例子

“$(echo ls)”替换为“ls”
“`echo ls`”替换为“ls”

待完善

（？不知道怎么理解？）
When the old-style backquote form of substitution is used, backslash retains its literal meaning except when followed by ‘$’, ‘'’, or ‘\’. The first backquote not preceded by a backslash terminates the command substitution. If the substitution appears within double quotes, word splitting and filename expansion are not performed on the results.