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The Fastest Way to Back Up a File in Bash (You’re Probably Not Using It)

Konstantinos Patronas

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Dec 15, 2025

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When working in the terminal, backing up a file before editing it is a habit that saves time, nerves, and sometimes entire systems. There’s a Bash trick that makes this almost effortless:

cp filename{,.bak}

How It Works

This command relies on brace expansion, a shell feature that generates multiple strings from a single pattern.

filename{,.bak}

expands to:

filename filename.bak

So Bash actually executes:

cp filename filename.bak

You type the filename once, and Bash handles the rest.

Why This Is Better Than the “Normal” Way

Most people write:

cp filename filename.bak

That works — but brace expansion has advantages:

• Faster typing
• Fewer mistakes, especially with long filenames
• Cleaner commands
• Easier to scan in scripts and terminal history

Once you get used to it, going back feels slow.

Real-World Examples