条件表达式中的语法错误

Question

我正在编写一个脚本，其中使用逻辑“OR”和逻辑“AND”语句的组合。这是脚本：

#!/bin/bash

echo "Enter the value of a"
read $a
echo "Enter the value of b"
read $b
if

[[ $a != STARTED && $b == STARTED ] || [ $b != STARTED && $a == STARTED ]]; then

echo "Either of the JVMs is not yet up, so lets wait for some more time"

i=$(($i+1))
sleep 1s

fi

并在执行时出现以下错误：

line 13: syntax error in conditional expression
line 13: syntax error near `]'
line 13: `[[ $a != STARTED && $b == STARTED ] || [ $b != STARTED && $a == STARTED ]]; then'

我正在使用 bash shell。非常感谢对此的任何帮助。

Answer 1

您[[与不匹配]。应始终以和with[[关闭。使用：]][]

if [[ $a != STARTED && $b == STARTED ]] || [[ $b != STARTED && $a == STARTED ]]; then

更好的是，因为你[[无论如何都在使用：

if [[ ($a != STARTED && $b == STARTED) || ($b != STARTED && $a == STARTED) ]]; then

另一个错误是您在执行以下操作，直到应用格式后我才注意到：

read $a
read $b

你应该这样做：

read a
read b

对于第一种形式，$a和$b被 shell 替换为它们的内容，所以如果您没有在此行之前设置它们，最终的命令将是：

read

（在这种情况下，读取的值将存储在变量中REPLY。）如果您设置了a某些值（例如a="blah blah"），则它看起来像：

read blah blah

Answer 2

代替：

[[ $a != STARTED && $b == STARTED ] || [ $b != STARTED && $a == STARTED ]]; then

我会用：

if [ $a != STARTED && $b == STARTED ] || [ $b != STARTED && $a == STARTED ]; then