Base64 Decode on Linux, Mac, and Windows — Command Line Guide

Every OS has a built-in way to decode Base64 from the terminal. The syntax is slightly different on each. Here is the exact command for every platform, plus a browser alternative when you do not want to open a terminal.

Linux

The base64 command is pre-installed on every major distro.

• Decode a string: echo "SGVsbG8gV29ybGQ=" | base64 -d
• Decode a file: base64 -d encoded.txt > decoded.txt
• Encode a string: echo -n "Hello World" | base64
• Encode a file: base64 input.txt > encoded.txt

The -n flag on echo is important when encoding. Without it, echo adds a trailing newline that gets included in the Base64 output.

macOS

macOS uses the BSD version of base64. The critical difference: use -D (capital) for decode, not -d.

• Decode: echo "SGVsbG8=" | base64 -D
• Encode: echo -n "Hello" | base64
• Decode file: base64 -D -i encoded.txt -o decoded.txt

If you use Homebrew and install coreutils, you get gbase64 which uses the same flags as Linux (-d for decode).

Windows

Windows does not have a simple base64 command.

PowerShell

• Decode: [System.Text.Encoding]::UTF8.GetString([System.Convert]::FromBase64String("SGVsbG8="))
• Encode: [System.Convert]::ToBase64String([System.Text.Encoding]::UTF8.GetBytes("Hello"))

Verbose, but it works. PowerShell 5+ is pre-installed on Windows 10 and 11.

CMD (certutil)

• Decode file: certutil -decode encoded.txt decoded.txt
• Encode file: certutil -encode input.txt encoded.txt

Only works with files, not inline strings. And the output includes a certificate header/footer that you may need to strip.

Quick Reference

Platform	Decode Command	Gotcha
Linux	echo "..." | base64 -d	Use -n on echo when encoding
macOS	echo "..." | base64 -D	Capital -D, not lowercase -d
PowerShell	[Convert]::FromBase64String(...)	Verbose syntax
CMD	certutil -decode file.txt out.txt	Files only, adds headers
Python	base64.b64decode("...").decode()	Works everywhere Python runs
Browser	Paste and click Decode	No syntax to remember

When the Command Line Is Overkill

If you need to quickly decode one string while reading documentation, debugging an API response, or checking a Kubernetes secret, opening a terminal and typing a command is slower than opening a browser tab.

The Base64 Encoder/Decoder handles both encoding and decoding with one click. No syntax differences between platforms, no flags to remember, full UTF-8 support built in.

Scripting and Automation

For scripts and CI/CD pipelines, the command-line tools are the right choice. Some tips:

• Always use echo -n (no trailing newline) when encoding
• For cross-platform scripts, Python's base64 module works identically everywhere
• In Docker/Kubernetes YAML, values are already Base64. Decode with: kubectl get secret name -o jsonpath='{.data.key}' | base64 -d

Related: URL Encoder for percent-encoding, JSON Formatter for API debugging.