Question

我在bash shell中输入命令：

#!/bin/bash
[[ a>2 ]];echo $?

我得到0

和另一个命令：

#!/bin/bash
[[ 3>2 ]];echo $?

我得到了

bash: unexpected token 283 in conditional command
bash: syntax error near `3>'

为什么我会犯这个错误？

如何在> <中使用[[ ]]？

我更加好奇，[[]]如何使用> <。 [[ a>2 ]];echo $?不添加空格，但[[ 3 > 2 ]]必须添加空格，对原因更加好奇

谢谢你！

Answer 1

由于bash builtins的手册页指出：＆＃34;每个运算符和操作数必须是一个单独的论点。＆＃34;

此外，您的变量a应为$a

以下是示例：

# Returns true
$ a=10;  [[ "$a" -gt 1 ]]; echo "$?"
0

# Returns false  
$ a=10;  [[ "$a" -gt 12 ]]; echo "$?"
1

以下内容可以帮助您

整数比较运算符

| Operator | Description                 | Example                                                  |
|----------|-----------------------------|----------------------------------------------------------|
| -eq      | Is Equal To                 | if [ $1 -eq 200 ]                                        |
| -ne      | Is Not Equal To             | if [ $1 -ne 1 ]                                          |
| -gt      | Is Greater Than             | if [ $1 -gt 15 ]                                         |
| -ge      | Is Greater Than Or Equal To | if [ $1 -ge 10 ]                                         |
| -lt      | Is Less Than                | if [ $1 -lt 5 ]                                          |
| -le      | Is Less Than Or Equal To    | if [ $1 -le 0 ]                                          |
| ==       | Is Equal To                 | if (( $1 == $2 )) [Note: Used within double parentheses] |
| !=       | Is Not Equal To             | if (( $1 != $2 ))                                        |
| <        | Is Less Than                | if (( $1 < $2 ))                                         |
| <=       | Is Less Than Or Equal To    | if (( $1 <= $2 ))                                        |
| >        | Is Greater Than             | if (( $1 > $2 ))                                         |
| >=       | Is Greater Than Or Equal To | if (( $1 >= $2 ))                                        |

字符串比较运算符

| Operator | Description                        | Example         | 
|----------|------------------------------------|-----------------| 
| = or ==  | Is Equal To                        | if [ $1 == $2 ] | 
| !=       | Is Not Equal To                    | if [ $1 != $2 ] | 
| >        | Is Greater Than (ASCII comparison) | if [ $1 > $2 ]  | 
| >=       | Is Greater Than Or Equal To        | if [ $1 >= $2 ] | 
| <        | Is Less Than                       | if [ $1 < $2 ]  | 
| <=       | Is Less Than Or Equal To           | if [ $1 <= $2 ] | 
| -n       | Is Not Null                        | if [ -n $1 ]    | 
| -z       | Is Null (Zero Length String)       | if [ -z $1 ]    |

bash：条件命令中的意外标记283

1 个答案: