Bash Error: Unary Operator Expected

Question

我正在尝试编写一个简单的 Bash 脚本，它将根据用户输入执行命令。我对 Python 有一些经验，但出于某种原因，这给我带来了问题。

===================

*#!/bin/bash
echo "Type one of the following:"
echo " 1 - whoami"
echo " 2 - df"
echo " 3 - date"
echo " 4 - cal"
echo "===> "
read $return_value
if [ $return_value -eq 1 ]
    then
        echo $whoami
elif [ $return_value -eq 2 ]
    then
        echo $df
elif [ $return_value -eq 3 ]
    then
        echo $date
elif [ $return_value -eq 4 ]
    then
        echo $cal
else [ $return_value != 5 ]
    echo "You made an invalid Selection. Exiting."
fi

========================================

我不断收到这组错误，我不知所措。

Type one of the following:
 1 - whoami
 2 - df
 3 - date
 4 - cal
===> 
2
./utilities1.sh: line 10: [: -eq: unary operator expected
./utilities1.sh: line 14: [: -eq: unary operator expected
./utilities1.sh: line 18: [: -eq: unary operator expected
./utilities1.sh: line 22: [: -eq: unary operator expected
./utilities1.sh: line 26: [: !=: unary operator expected
You made an invalid Selection. Exiting.

如有任何建议或提示，我们将不胜感激。

Answer 1

试试这个：read return_value 没有 $ 符号。

选择选项后不会调用您的命令，因为 $whoami 被视为变量。你可能想要 $(whoami)。其他命令也一样。

Answer 2

这里有多个问题。

首先，您显然是想 read return_value 而不是 read $return_value，将用户输入读取到名为 return_value 的变量中。 read $return_value 会将用户输入读取到一个名为 $return_value 的变量中。例如，如果 return_value=x，那么它会将输入读入变量 x。由于在运行脚本时未分配 return_value，这不是您想要的。你肯定想要 read return_value.

其次，您可能想要执行那些命令而不是 echo $df 和其他命令。

此外，如果用户简单地按下 enter，$return_value 的值将为空，这将再次破坏条件。所以你应该在 if 和 elif 语句中双引号。

像这样：

#!/bin/bash

echo "Type one of the following:"
echo " 1 - whoami"
echo " 2 - df"
echo " 3 - date"
echo " 4 - cal"
echo "===> "
read return_value

if [ "$return_value" -eq 1 ]; then
    whoami
elif [ "$return_value" -eq 2 ]; then
    df
elif [ "$return_value" -eq 3 ]; then
    date
elif [ "$return_value" -eq 4 ]; then
    cal
else [ "$return_value" != 5 ]
    echo "You made an invalid Selection. Exiting."
fi

Answer 3

我认为这还不清楚，可以使用更多规范来明确您要键入的内容。如果您希望用户键入“1”，那么请说出来，而不是“1 - whoami”。我也不清楚你开头的“*”。这是一个工作代码，注释中有解释。希望这对您有所帮助。

#!/bin/bash
echo "Type one of the following numbers to"
echo "execute the specified command:"
echo " 1 - whoami"
echo " 2 - df"
echo " 3 - date"
echo " 4 - cal";
echo -n "===> "    #the -n means dont create a newline.. so the input will be after the arrow
read return_value  #remove $
echo "user input = ${return_value}"   #using ${} instead of just $ is good practice unless you have reason
if [ "${return_value}" == "1" ]; then  #sometimes you need = instead, compatibility issues.  but -eq is for integers.
    echo `whoami`                       #surround a command with `command` to execute it
elif [ "${return_value}" == "2" ]; then
    echo `df`
elif [ "${return_value}" == "3" ]; then
    echo `date`
elif [ "${return_value}" == "4" ]; then #don't forget the ";" before "then"
    echo `cal`
else                                    #else doesn't need an argument like if and elif
    echo "You made an invalid Selection. Exiting."
fi

示例输出：

me$ ./script.sh 
Type one of the following numbers to
execute the specified command:
 1 - whoami
 2 - df
 3 - date
 4 - cal
===> 1
user input = 1
myusername

Bash Error: Unary Operator Expected

Bash Error: Unary Operator Expected

variables

bash

conditional