simple_decoder.sh

#!/bin/bash

# decode from Base64
decode_base64() {
    if command -v base64 &> /dev/null; then
        echo -n "$1" | base64 -d
    else
        echo "Base64 decoding tool not found."
    fi
}

# decode from Base32
decode_base32() {
    if command -v base32 &> /dev/null; then
        echo -n "$1" | base32 -d
    else
        echo "Base32 decoding tool not found."
    fi
}

# decode from Base16 (Hexadecimal)
decode_base16() {
    if command -v xxd &> /dev/null; then
        echo -n "$1" | xxd -r -p
    else
        echo "Hexadecimal decoding tool not found."
    fi
}

# decode HTML entities
decode_html() {
    echo "$1" | sed 's/&amp;/\&/g; s/&lt;/</g; s/&gt;/>/g; s/&quot;/"/g; s/&#39;/'\''/g'
}

# decode URL-encoded strings
decode_url() {
    echo "$1" | python3 -c "import urllib.parse, sys; print(urllib.parse.unquote(sys.stdin.read().strip()))"
}

# decode Binary encoded strings
decode_binary() {
    binary_string=$(echo "$1" | tr -d ' ')
    length=${#binary_string}
    decoded_string=""

    for ((i=0; i<length; i+=8)); do
        byte=${binary_string:i:8}
        decimal=$((2#$byte))
        decoded_string+=$(printf "\\x%x" "$decimal")
    done

    echo -e "$decoded_string"
}

# decode Octal encoded strings
decode_octal() {
    echo "$1" | awk '{for(i=1;i<=NF;i++)printf("%c",strtonum("0"$i));print""}'
}

# detect encoding type
detect_encoding() {
    if echo "$1" | grep -qE '^[0-9A-Fa-f]+$'; then
        echo "The string appears to be Base16 (Hexadecimal)."
        return 1
    elif echo "$1" | grep -qE '^[A-Z2-7=]+$'; then
        echo "The string appears to be Base32."
        return 2
    elif echo "$1" | grep -qE '^[A-Za-z0-9+/=]+$'; then
        echo "The string appears to be Base64."
        return 3
    elif echo "$1" | grep -qE '(&amp;|&lt;|&gt;|&quot;|&#39;)'; then
        echo "The string appears to be HTML encoded."
        return 4
    elif echo "$1" | grep -qE '(%[0-9A-Fa-f]{2})+'; then
        echo "The string appears to be URL encoded."
        return 5
    elif echo "$1" | grep -qE '^[01 ]+$'; then
        echo "The string appears to be Binary encoded."
        return 6
    elif echo "$1" | grep -qE '^[0-7 ]+$'; then
        echo "The string appears to be Octal encoded."
        return 7
    else
        echo "Unable to detect encoding type."
        return 0
    fi
}

# Get the string to decode
read -p "Enter the string to decode: " input_string

# detect the encoding type
detect_encoding "$input_string"
encoding_type=$?

# user do you want to decode?
if [ $encoding_type -ne 0 ]; then
    read -p "Do you want to decode it? (yes/no) " decode_choice
    if [ "$decode_choice" == "yes" ]; then
        case $encoding_type in
            1)
                decoded=$(decode_base16 "$input_string")
                ;;
            2)
                decoded=$(decode_base32 "$input_string")
                ;;
            3)
                decoded=$(decode_base64 "$input_string")
                ;;
            4)
                decoded=$(decode_html "$input_string")
                ;;
            5)
                decoded=$(decode_url "$input_string")
                ;;
            6)
                decoded=$(decode_binary "$input_string")
                ;;
            7)
                decoded=$(decode_octal "$input_string")
                ;;
            *)
                echo "Invalid encoding type detected."
                exit 1
                ;;
        esac

        if [ -z "$decoded" ]; then
            echo "Decoding failed or tool not available."
        else
            echo "Decoded string: $decoded"
        fi
    else
        echo "Decoding aborted."
    fi
fi