对于"if"的测试-s.陈述 [英] the test -s for the "if" statement

问题描述

我有一个问题，如果有人知道我的回答，我将不胜感激.好的，到这一点.在我的一个脚本中，我有以下表达式，对于表单手册页来说，尚不清楚它应该产生什么效果:

I have a question and i would be grateful for the answer if somebody knows one. Ok, to the point. In one of my scripts i have following expression, it is not clear for me form man page what effect it should produce:

如果！[[-s"$ the_file_to_check"]];然后回显文件大小为零且不存在|存在且大小为零|不为零大小且不存在|不为零大小或不存在|不存在(显然为零大小)"；fi

存在单独的存在性检查(-a键)，为什么还要添加另一个检查?

there exist separate check for existence (the -a key), why to add another one?

以及这种逻辑如何工作.

And how this logics works in anyway.

我的定义有些失落.

P.S.
我需要检查是否为空，但不存在.谢谢大家.

P.S.
I need a check for emptiness but not existence. Thank everyone.

推荐答案

-s 不仅检查文件是否存在，还检查文件是否包含任何数据(即文件是否大小)大于0个字节).这比 -a 选项(实际上是 -e 的同义词)所做的更多，后者仅测试文件是否存在.

-s checks not only if the file exists, but also if it contains any data (that is, if it has a size greater than 0 bytes). This is more than the -a option (which is, in fact, a synonym of -e) does, which only tests if the file exists.

touch foo
[[ -a foo ]] && echo "File foo exists"
[[ -s foo ]] || echo "File foo exists, but is size 0 bytes"

(我想知道 -a 的原理是什么，因为我不知道它的作用与 -e 有所不同.)

(I have wondered what the rationale for -a is, since I'm not aware that it does anything different from -e.)

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