How to Find All Combinations of 4 Numbers Using Bash

Generating every possible combination of 4 numbers is a surprisingly common task — whether you're writing test data, exploring number patterns, solving a puzzle, or automating a security audit. Bash gives you several clean ways to do this, each with trade-offs depending on what "combination" actually means in your situation.

What "Combinations" Actually Means Here

Before writing a single line of Bash, it's worth getting precise about terminology, because the word combination gets used loosely:

• Permutations — order matters. 1234 and 4321 are different results.
• Combinations — order doesn't matter. 1234 and 4321 are the same group.
• With repetition — digits can repeat: 1112, 9999, etc.
• Without repetition — each digit used only once per sequence.

Most people searching for this topic want one of two things: either all 4-digit sequences from a set of digits (permutations with repetition, like generating every PIN from 0000–9999), or unique groupings where order doesn't matter and digits don't repeat (true combinations). The Bash approach differs meaningfully between these two cases.

Generating All 4-Digit Sequences (0000–9999) 🔢

If your goal is every possible 4-digit number — including leading zeros — a simple nested loop or brace expansion handles it efficiently.

Using nested loops: