git / zero sha

updated May 29, 2026

A zero SHA is a commit hash made of only 0 characters. Git uses it as a null object ID for refs that point nowhere.

For SHA-1 repos, it is 40 zeros:

0000000000000000000000000000000000000000

For SHA-256 repos, it is 64 zeros:

0000000000000000000000000000000000000000000000000000000000000000

Where it appears

You usually see zero SHAs in push events and hooks, not in normal git log output.

In push semantics:

• branch creation: before is zero, after is the first commit
• branch deletion: before is the old commit, after is zero

Webhook payloads may also send before as an empty string on branch creation. Treating empty and zero as equivalent makes handlers resilient.

Practical check in Go

func isZeroSHA(sha string) bool {
	sha = strings.TrimSpace(sha)
	if sha == "" {
		return true
	}
	if len(sha) != 40 && len(sha) != 64 {
		return false
	}
	for _, r := range sha {
		if r != '0' {
			return false
		}
	}
	return true
}

Then branch your logic:

switch {
case isZeroSHA(before):
	fmt.Println("branch created")
case isZeroSHA(after):
	fmt.Println("branch deleted")
default:
	fmt.Println("normal push")
}

Why this matters

Without a zero-SHA check, automation can misclassify branch creation and deletion events. That can trigger noisy automation and incorrect event handling.

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