.sh 文件出现问题，出现意外标记

Question

因此我写了下面的脚本：

#!/bin/bash
 
echo "Enter a number:"
read num
 
if [ $num -gt 0 ]; then
  echo "$num is positive."
elif [ $num == 0 ]; then
  echo "$num is zero."
else
  echo "$num is negative."
fi

它给了我syntax error in line 6: then unexpected token