关键字"if"如何测试值是true还是false? [英] How does the keyword “if” test if a value is true or false?

问题描述

在bash脚本中

if [ 1 ]
then
   echo "Yes"
else
   echo "No"
fi

输出:是

它表示将'1'视为真实值.

It represents that '1' is treated as true value.

但是在代码中:

word = Linux
letter = nuxi
if echo "$word" | grep -q "$letter"
then
    echo "Yes"
else
    echo "No"
fi

输出:否

但是 echo"$ word" |grep -q"$ letter" 将返回1，所以为什么结果是 No .

But echo "$word" | grep -q "$letter" will return 1, so why is the result is No.

关键字 if 如何测试 if 之后的命令返回的值?

How does the keyword if test the value returned by the command after if?

推荐答案

检查命令的返回值. [1] 的返回值是 0 (true).其他任何返回值(例如 1 )都表示错误.

The return value of a command is checked. [ 1 ] has a return value of 0 (true). Any other return value (like 1) indicates an error.

您可以使用 $?变量显示上次执行的命令的返回值:

You can display the return value of the last executed command using the $? variable:

true
echo $?
# returned 0
false
echo $?
# returned 1
echo $?
# returned 0 as the last executed command is 'echo', and not 'false'

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