用shell编写一个凯撒密码的加解密脚本

以下是一个用Shell编写的凯撒密码加解密脚本：

#!/bin/bash

# 凯撒密码加解密脚本

# 加密函数
encrypt() {
    local plaintext="$1"
    local shift="$2"
    local ciphertext=""

    for (( i=0; i<${#plaintext}; i++ )); do
        char="${plaintext:$i:1}"
        if [[ "$char" =~ [a-z] ]]; then
            ciphertext+="$(echo $char | tr "a-z" "$(printf %${shift}s | tr " " ".;\\[/")a-z")"
        elif [[ "$char" =~ [A-Z] ]]; then
            ciphertext+="$(echo $char | tr "A-Z" "$(printf %${shift}s | tr " " ".;\\[/")A-Z")"
        else
            ciphertext+="$char"
        fi
    done

    echo "$ciphertext"
}

# 解密函数
decrypt() {
    local ciphertext="$1"
    local shift="$2"
    local plaintext=""

    for (( i=0; i<${#ciphertext}; i++ )); do
        char="${ciphertext:$i:1}"
        if [[ "$char" =~ [a-z] ]]; then
            plaintext+="$(echo $char | tr "$(printf %${shift}s | tr " " ".;\\[/")a-z" "a-z")"
        elif [[ "$char" =~ [A-Z] ]]; then
            plaintext+="$(echo $char | tr "$(printf %${shift}s | tr " " ".;\\[/")A-Z" "A-Z")"
        else
            plaintext+="$char"
        fi
    done

    echo "$plaintext"
}

# 主程序
if [[ "$1" == "encrypt" ]]; then
    plaintext="$2"
    shift="$3"

    if [[ -z "$plaintext" || -z "$shift" ]]; then
        echo "Usage: $0 encrypt <plaintext> <shift>"
        exit 1
    fi

    ciphertext="$(encrypt "$plaintext" "$shift")"
    echo "$ciphertext"

elif [[ "$1" == "decrypt" ]]; then
    ciphertext="$2"
    shift="$3"

    if [[ -z "$ciphertext" || -z "$shift" ]]; then
        echo "Usage: $0 decrypt <ciphertext> <shift>"
        exit 1
    fi

    plaintext="$(decrypt "$ciphertext" "$shift")"
    echo "$plaintext"

else
    echo "Usage: $0 {encrypt|decrypt} <text> <shift>"
    exit 1
fi

使用方法：

1. 将以上脚本保存为 `caesar.sh` 文件。
2. 在终端中执行以下命令使脚本可执行：`chmod +x caesar.sh`
3. 对明文进行加密：`./caesar.sh encrypt "明文" 3`，其中 `3` 表示移位数。
4. 对密文进行解密：`./caesar.sh decrypt "密文" 3`，其中 `3` 表示移位数。

注意：以上脚本只支持英文字符的加解密。如果需要支持其他语言或字符集，请根据需要进行修改。