空值Bash中的空字符串比较 [英] Null & empty string comparison in Bash

问题描述

我没有为$ pass_tc11设置任何值；因此它在回显时返回null.如何在 if 子句中进行比较?

I don't set any values for $pass_tc11; so it is returning null while echoing. How to compare it in if clause?

这是我的代码.我不希望打印嗨" ...

-bash-3.00$ echo $pass_tc11

-bash-3.00$ if [ "pass_tc11" != "" ]; then
> echo "hi"
> fi
hi
-bash-3.00$

推荐答案

首先，请注意您没有正确使用变量:

First of all, note you are not using the variable correctly:

if [ "pass_tc11" != "" ]; then
#     ^
#     missing $

无论如何，要检查变量是否为空，可以使用 -z ->字符串为空:

Anyway, to check if a variable is empty or not you can use -z --> the string is empty:

if [ ! -z "$pass_tc11" ]; then
   echo "hi, I am not empty"
fi

或 -n ->长度不为零:

if [ -n "$pass_tc11" ]; then
   echo "hi, I am not empty"
fi

来自 man test :

-z STRING

STRING的长度为零

the length of STRING is zero

-n STRING

STRING的长度不为零

the length of STRING is nonzero

示例:

$ [ ! -z "$var" ] && echo "yes"
$

$ var=""
$ [ ! -z "$var" ] && echo "yes"
$

$ var="a"
$ [ ! -z "$var" ] && echo "yes"
yes

$ var="a"
$ [ -n "$var" ] && echo "yes"
yes

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