如何缩短它？：先阅读|| 1号出口； （回声“$first”；猫）| $foo
目的是如果没有输入，甚至不启动 $foo。
如果 foo="diff - xyz" 并且输入丢失或为空，这可能很有用。 否则，diff 将输出所有“xyz”作为差异。
最初的问题是“cat doesnotexist | diff - Exists”输出“exists”的内容（前缀为“>”），而我希望整个管道失败。 我当前的解决方案是：
cat doesnotexist | (read first|| exit 1; (echo "$first"; cat) | diff - exists)
，但我想要一个更短的解决方案。
The aim is to not even start $foo if there is no input.
This can be useful if foo="diff - xyz", and the input is missing or empty.
Otherwise, diff would output all of "xyz" as the difference.
The original problem is that "cat doesnotexist | diff - exists" outputs the content of "exists" (prefixed with ">"), while I want the entire pipe to fail.
My current solution is:
cat doesnotexist | (read first|| exit 1; (echo "$first"; cat) | diff - exists)
, but I would like a shorter one.
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我删除了管道，它在您的示例中没有附加值。严格来说，这不会让 diff 失败，只是没有执行。
I removed the pipe, it has no added value in your example. Strictly, this doesn't let the diff fail, it's just not executed.