另一种方法，这里还没有提到的是在无限while循环中初始化参数。下面不是最清晰的示例，但它达到了它的目的。

#!/usr/bin/env bash
[ "$1" ] && foo=0 && bar="baz"
while : "${foo=2}" "${bar:=qux}"; do
    echo "$foo"
    (( foo == 3 )) && echo "$bar" && break
    (( foo=foo+1 ))
done

:的一个有用的应用程序是，如果您只对使用参数展开的副作用感兴趣，而不是实际将其结果传递给命令。

在这种情况下，您使用参数展开作为参数:或false，这取决于您想要的退出状态是0还是1。一个例子是

: "${var:=$1}"

由于:是内置的，它应该相当快。

它对多语言程序也很有用:

#!/usr/bin/env sh
':' //; exec "$(command -v node)" "$0" "$@"
~function(){ ... }

现在这既是一个可执行的shell脚本，也是一个JavaScript程序:这意味着。/filename.js、sh filename.js和node filename.js都可以工作。

(这种用法确实有点奇怪，但还是很有效。)

请作一些说明:

Shell-scripts are evaluated line-by-line; and the exec command, when run, terminates the shell and replaces it's process with the resultant command. This means that to the shell, the program looks like this: #!/usr/bin/env sh ':' //; exec "$(command -v node)" "$0" "$@" As long as no parameter expansion or aliasing is occurring in the word, any word in a shell-script can be wrapped in quotes without changing its' meaning; this means that ':' is equivalent to : (we've only wrapped it in quotes here to achieve the JavaScript semantics described below) ... and as described above, the first command on the first line is a no-op (it translates to : //, or if you prefer to quote the words, ':' '//'. Notice that the // carries no special meaning here, as it does in JavaScript; it's just a meaningless word that's being thrown away.) Finally, the second command on the first line (after the semicolon), is the real meat of the program: it's the exec call which replaces the shell-script being invoked, with a Node.js process invoked to evaluate the rest of the script. Meanwhile, the first line, in JavaScript, parses as a string-literal (':'), and then a comment, which is deleted; thus, to JavaScript, the program looks like this: ':' ~function(){ ... } Since the string-literal is on a line by itself, it is a no-op statement, and is thus stripped from the program; that means that the entire line is removed, leaving only your program-code (in this example, the function(){ ... } body.)

我用它来轻松地启用/禁用变量命令:

#!/bin/bash
if [[ "$VERBOSE" == "" || "$VERBOSE" == "0" ]]; then
    vecho=":"     # no "verbose echo"
else
    vecho=echo    # enable "verbose echo"
fi

$vecho "Verbose echo is ON"

Thus

$ ./vecho
$ VERBOSE=1 ./vecho
Verbose echo is ON

这有助于编写干净的脚本。这不能用'#'完成。

同时,

: >afile

是保证'afile'存在但长度为0的最简单方法之一。

它类似于Python中的传递。

一种用法是将一个函数存根，直到它被写入:

future_function () { :; }

你可以将它与反撇号(' ')结合使用来执行命令而不显示输出，如下所示:

: `some_command`

当然，你可以只执行some_command > /dev/null，但是:-version稍微短一些。

话虽如此，我不建议这样做，因为这会让人们感到困惑。它只是作为一个可能的用例出现在脑海中。