Bash 脚本 - if 块中的布尔值？
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Bash scripting - Boolean in if block?
提问by Steam
I tried the code in this SO post - How to evaluate a boolean variable in an if block in bash?and it does not work. It looks like there are no booleans in BASH. Is there a flawless workaround which lets me set and check booleans in BASH ?
我尝试了这篇 SO 帖子中的代码 -如何在 bash 的 if 块中评估布尔变量？它不起作用。看起来 BASH 中没有布尔值。是否有完美的解决方法可以让我在 BASH 中设置和检查布尔值？
My code -
我的代码 -
#!/bin/bash
flag=true
if [ $flag ]
echo 'True'
#flag=false
#echo 'Now changed to false'
fi
Even if flag=false in line 2, output is still True. Why ?
即使第 2 行中的 flag=false，输出仍然为 True。为什么 ？
回答by Cristian Meneses
Try without square brackets, like this
尝试不使用方括号，像这样
#!/bin/bash
flag=true
if $flag ; then
echo 'True'
#flag=false
#echo 'Now changed to false'
fi
回答by Omeganon
It evaluates to true because of this part of 'man test' -
由于“人测试”的这一部分，它评估为真 -
[ expression ]
string True if string is not the null string.
You need to use something like -
你需要使用类似的东西 -
#!/bin/bash
flag=1
if [ ${flag} -eq 1 ]
then
echo 'True'
#flag=0
#echo 'Now changed to false'
fi
