Base64 in Bash and PowerShell CLI

Sometimes you need to quickly encode a string or a file for a configuration file, SSH key, or Kubernetes secret, and you don't want to open a web browser or write a Python script.

Fortunately, macOS, Linux, and Windows all include native command-line utilities for working with Base64.

1. Linux & macOS (Bash/Zsh)

On UNIX-like systems, the base64 core utility is installed by default. You can pipe data into it via standard input (stdin).

Encoding Strings

Remember to use -n with echo.

# Correct: Encodes exactly "hello world"
echo -n "hello world" | base64
# Output: aGVsbG8gd29ybGQ=

# Incorrect: Encodes "hello world\n"
echo "hello world" | base64
# Output: aGVsbG8gd29ybGQK

Decoding Strings

To decode, pass the --decode flag (or -d on most Linux distributions, -D on older macOS).

echo -n "aGVsbG8gd29ybGQ=" | base64 --decode
# Output: hello world

Encoding and Decoding Files

You can also pass a file directly to the base64 command.

# Encode a file
base64 my_secret.key > encoded.txt

# Decode a file
base64 --decode encoded.txt > decoded.key

2. Windows (PowerShell)

Windows doesn't have a native base64 executable, but PowerShell provides access to the robust .NET System.Convert class.

Encoding Strings

$text = "hello windows"
$bytes = [System.Text.Encoding]::UTF8.GetBytes($text)
$base64 = [System.Convert]::ToBase64String($bytes)

Write-Output $base64
# Output: aGVsbG8gd2luZG93cw==

Decoding Strings

$base64 = "aGVsbG8gd2luZG93cw=="
$bytes = [System.Convert]::FromBase64String($base64)
$text = [System.Text.Encoding]::UTF8.GetString($bytes)

Write-Output $text
# Output: hello windows

Bonus: certutil (Windows CMD)

If you are stuck in the old Windows Command Prompt (cmd.exe) and need to encode a file without PowerShell, you can use the built-in certificate utility certutil.

# Encode a file to Base64
certutil -encode input.txt output.b64

# Decode a Base64 file
certutil -decode output.b64 input.txt