Master Base64 Encoding and Decoding on the Command Line

Base64 is a method for converting binary data into ASCII characters, which is useful when transmitting data through text‑only systems that cannot handle raw binary.

What Base64 Is Used For

Data compression

Data hiding

Transmitting data in an alternative format

Base64 encoded data may only contain letters, digits, and the = padding character. For example, c2FtcGxlCg== is valid, while HV3.Zh2J== is not.

Base64 Command Syntax

The basic syntax for the GNU base64 utility is:

$ base64 [OPTION] [FILE]

Common Options

Decode a file or string: -d or --decode Show help information: --help Ignore non‑alphabet characters when decoding: -i, --ignore-garbage Show version information:

--version

Encoding a String

To encode the text “Welcome to Linux”: $ echo "Welcome to Linux" | base64 The command prints the Base64 representation to standard output. You can also redirect the output to a file:

$ echo "Welcome to Linux" | base64 > encodedfile.txt

View the saved file with:

$ cat encodedfile.txt

Decoding a String

To decode the Base64 string “V2VsY29tZSB0byBMaW51eAo=”:

$ echo "V2VsY29tZSB0byBMaW51eAo=" | base64 --decode

The original text is printed to standard output:

You can also redirect the decoded output to a file:

$ echo "V2VsY29tZSB0byBMaW51eAo=" | base64 --decode > decodedfile.txt

Encoding a Text File

Encode the contents of testfile.txt:

$ base64 testfile.txt

Redirect the output to a file if needed:

$ base64 -d encodedfile.txt > decodedfile.txt

Encoding User Input with a Script

The following Bash script reads data from the user, encodes it with Base64, and prints the result:

#!/bin/bash
# Prompt for input
echo "Provide Some data to encode"
# Read input into variable
read data
# Encode and store in variable
encod_data=`echo -n $data | base64`
# Print encoded output
echo "Encoded text is : $encod_data"

Verifying a User Key

This script decodes a predefined Base64 key and compares it with user input to validate the key:

#!/bin/bash
# Prompt for key
echo "Enter your key"
read key
# Decode predefined key
orig_key=`echo 'QWJjMTIzCg==' | base64 --decode`
# Compare
if [ $key == $orig_key ]; then
  echo "You have entered a valid key"
else
  echo "The key you have entered is not valid"
fi

Note that encoding is not encryption; encoded data can be easily decoded, so Base64 should not be used to protect sensitive information.