如何编写基于菜单的LUKS加密Bash脚本，解决cryptsetup报错问题

你脚本中的变量赋值逻辑存在语法错误，所有加密配置类变量（cipher、key、hash、pbkdf）都未被正确赋值，空值传入cryptsetup命令后触发数值无效报错。
你混淆了Bash中条件判断和变量赋值的语法：[[ 变量 == 值 ]]是判断两个值是否相等的条件表达式，不会执行赋值操作，脚本运行完所有选择逻辑后，上述变量全部是空值，导致cryptsetup的-s（密钥长度）等需要数值的参数没有拿到合法输入。

将所有条件分支内的条件判断语句替换为标准变量赋值语句，格式为变量名="值"，不需要包裹双括号。
另外建议新增非法输入退出逻辑，避免用户选错选项后脚本依然携带空参数执行加密操作。

#!/usr/bin/env bash

## Ask user for device.
echo "Device:" 
read -r device

## Ask user for cipher.
echo "Available ciphers:" 
echo "AES     [0]" 
echo "Serpent [1]" 
echo "Twofish [2]" 
echo "Cipher:" 
read -r cipherin
if [[ $cipherin == "0" ]]; then
        cipher="aes-xts-plain64"
elif [[ $cipherin == "1" ]]; then
        cipher="serpent-xts-plain64"
elif [[ $cipherin == "2" ]]; then
        cipher="twofish-xts-plain64"
else 
        echo "Invalid choice."
        exit 1
fi

## Ask user for key length.
echo "Available key lengths (bits):" 
echo "128 [0]" 
echo "256 [1]" 
echo "Key length:" 
read -r keyin
if [[ $keyin == "0" ]]; then
        key="256"
elif [[ $keyin == "1" ]]; then
        key="512"
else 
        echo "Invalid choice."
        exit 1
fi

## Ask user for hash.
echo "Available hashes:" 
echo "SHA-1     [0]" 
echo "SHA-256   [1]" 
echo "SHA-512   [2]" 
echo "Whirlpool [3]:" 
echo "Hash:" 
read -r hashin
if [[ $hashin == "0" ]]; then
        hash="sha1"
elif [[ $hashin == "1" ]]; then
        hash="sha256"
elif [[ $hashin == "2" ]]; then
        hash="sha512"
elif [[ $hashin == "3" ]]; then
        hash="whirlpool"
else 
        echo "Invalid choice."
        exit 1
fi

## Ask user for PBKDF.
echo "Available PBKDFs:" 
echo "argon2i  [0]" 
echo "argon2id [1]" 
echo "pbkdf2   [2]"
read -r pbkdfin
if [[ $pbkdfin == "0" ]]; then
        pbkdf="argon2i"
elif [[ $pbkdfin == "1" ]]; then
        pbkdf="argon2id"
elif [[ $pbkdfin == "2" ]]; then
        pbkdf="pbkdf2"
else 
        echo "Invalid choice."
        exit 1
fi

## Ask user for iteration time.
echo "Iteration time (ms):" 
read -r iteration

## Encrypt drive using LUKS.
echo "Encrypting..." 
sudo cryptsetup --type luks2 -c "${cipher}" -h "${hash}" \
 -i "${iteration}" -s "${key}" --pbkdf "${pbkdf}" --use-urandom \
 -y luksFormat "${device}"

修改时同时给所有变量加上了双引号避免路径/参数含空格时出错，read加了-r参数避免转义符异常，所有非法输入分支新增exit 1直接终止脚本，防止无效参数被传入加密命令。

内容的提问来源于stack exchange，提问作者user16448786