Shell脚本中Case分支嵌套If-else的语法错误排查求助

编写的Shell脚本包含Case语句，且在c分支中嵌套了If-else逻辑，选择选项c时触发语法错误，报错信息如下：

./a.sh: 27: Syntax error: ";;" unexpected (expecting "fi")

原脚本 #

#!/bin/sh

echo Enter choice :
echo a : To create a file, name given by user.
echo b : To copy file to another location.
echo c : To determine minimum age to vote.

read choice
case $choice in

    a) echo Enter the name of file.
        read name
        mkdir $name ;; 
    b) echo Enter file name you want to copy
        read  file_name
      echo Enter location where you want to copy $file_name
        read location
        cp -r  $file_name "$location";;
    c) echo Enter age :
        read age
        if [ age -ge 18 ]
        then 
        echo You are eligible 
        else 
        echo You are not eligible
        "fi" 
        ;;        
    *) echo Please! Enter correct choice.
 
esac

错误输出 #

Enter choice :
a : To create a file, name given by user.
b : To copy file to another location.
c : To determine minimum age to vote.
c
./a.sh: 27: Syntax error: ";;" unexpected (expecting "fi")

问题原因及修复 #

1. If语句结束关键字错误：c分支中的"fi"被加了双引号，Shell会将其视为字符串命令而非结束if的关键字，导致if语句未正确闭合，后续的;;触发语法错误。需去掉引号，直接写fi。
2. 变量引用错误：if [ age -ge 18 ]中直接写age会被当成字符串字面量，无法读取输入的年龄变量，应改为$age来引用变量。

修正后的完整脚本 #

#!/bin/sh

echo Enter choice :
echo a : To create a file, name given by user.
echo b : To copy file to another location.
echo c : To determine minimum age to vote.

read choice
case $choice in

    a) echo Enter the name of file.
        read name
        mkdir $name ;; 
    b) echo Enter file name you want to copy
        read  file_name
        echo Enter location where you want to copy $file_name
        read location
        cp -r  $file_name "$location";;
    c) echo Enter age :
        read age
        if [ $age -ge 18 ]
        then 
            echo You are eligible 
        else 
            echo You are not eligible
        fi 
        ;;        
    *) echo Please! Enter correct choice.
 
esac

内容的提问来源于stack exchange，提问作者Satendra Patel