假设您想要找到与gcc安装位置对应的lib目录。你有一个选择:

libdir=$(dirname $(dirname $(which gcc)))/lib

libdir=`dirname \`dirname \\\`which gcc\\\`\``/lib

第一种方法比第二种简单——使用第一种方法。

POSIX标准定义了命令替换的$(命令)形式。目前使用的大多数shell都是POSIX兼容的，并且支持这种首选形式，而不是古老的反刻度符号。Shell Language文档的命令替换部分(2.6.3)描述了以下内容:

Command substitution allows the output of a command to be substituted in place of the command name itself.  Command substitution shall occur when the command is enclosed as follows: $(command) or (backquoted version): `command` The shell shall expand the command substitution by executing command in a subshell environment (see Shell Execution Environment) and replacing the command substitution (the text of command plus the enclosing "$()" or backquotes) with the standard output of the command, removing sequences of one or more <newline> characters at the end of the substitution. Embedded <newline> characters before the end of the output shall not be removed; however, they may be treated as field delimiters and eliminated during field splitting, depending on the value of IFS and quoting that is in effect. If the output contains any null bytes, the behavior is unspecified. Within the backquoted style of command substitution, <backslash> shall retain its literal meaning, except when followed by: '$' , '`', or <backslash>. The search for the matching backquote shall be satisfied by the first unquoted non-escaped backquote; during this search, if a non-escaped backquote is encountered within a shell comment, a here-document, an embedded command substitution of the $(command) form, or a quoted string, undefined results occur. A single-quoted or double-quoted string that begins, but does not end, within the "`...`" sequence produces undefined results. With the $(command) form, all characters following the open parenthesis to the matching closing parenthesis constitute the command. Any valid shell script can be used for command, except a script consisting solely of redirections which produces unspecified results. The results of command substitution shall not be processed for further tilde expansion, parameter expansion, command substitution, or arithmetic expansion. If a command substitution occurs inside double-quotes, field splitting and pathname expansion shall not be performed on the results of the substitution. Command substitution can be nested. To specify nesting within the backquoted version, the application shall precede the inner backquotes with <backslash> characters; for example: \`command\` The syntax of the shell command language has an ambiguity for expansions beginning with "$((", which can introduce an arithmetic expansion or a command substitution that starts with a subshell. Arithmetic expansion has precedence; that is, the shell shall first determine whether it can parse the expansion as an arithmetic expansion and shall only parse the expansion as a command substitution if it determines that it cannot parse the expansion as an arithmetic expansion. The shell need not evaluate nested expansions when performing this determination. If it encounters the end of input without already having determined that it cannot parse the expansion as an arithmetic expansion, the shell shall treat the expansion as an incomplete arithmetic expansion and report a syntax error. A conforming application shall ensure that it separates the "$(" and '(' into two tokens (that is, separate them with white space) in a command substitution that starts with a subshell. For example, a command substitution containing a single subshell could be written as: $( (command) )

除了其他答案，

$(...)

在视觉上更突出

`...`

反撇号看起来太像撇号了;这取决于你使用的字体。

(而且，正如我刚刚注意到的，在内联代码示例中输入反撇号要困难得多。)

在2021年，有必要提到一个奇怪的事实，作为对其他答案的补充。

Microsoft DevOps YAML管道“脚本”可能包含Bash任务。但是，符号$()用于引用YAML上下文中定义的变量，因此在这种情况下，应该使用反引号来捕获命令的输出。

在将脚本代码复制到YAML脚本时，这主要是一个问题，因为DevOps预处理器对不存在的变量非常宽容，所以不会出现任何错误消息。

$()允许嵌套。

out=$(echo today is $(date))

我觉得倒勾是不允许的。

假设您想要找到与gcc安装位置对应的lib目录。你有一个选择:

libdir=$(dirname $(dirname $(which gcc)))/lib

libdir=`dirname \`dirname \\\`which gcc\\\`\``/lib

第一种方法比第二种简单——使用第一种方法。