Pattern

Regex for SHA-1 hash

40-character SHA-1 hash.

The SHA-1 hash regex is ^[0-9a-fA-F]{40}$ — copy it below, or open it in the explainer for a token-by-token breakdown.

The pattern

^[0-9a-fA-F]{40}$

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What it matches

356a192b7913b04c54574d18c28d46e6395428ab
DA39A3EE5E6B4B0D3255BFEF95601890AFD80709

What it doesn't match

short
356a192b7913b04c54574d18c28d46e639542

Notes & gotchas

Same length as a Git commit SHA. SHA-1 is deprecated for security but still used in legacy systems.

Code in your language

Use the explainer's Code tab to generate ready-to-paste snippets in JavaScript, Python, Java, .NET, Go, Ruby, and PHP for this pattern.

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Token-by-token breakdown

Every part of the pattern, left to right:

Token	Meaning
`^`	start of string (or line in multiline mode)
`[0-9a-fA-F]{40}`	exactly 40 times: any of: digits, a–f, A–F
`$`	end of string (or line in multiline mode)

About this pattern

Identifier formats like UUIDs, hashes, and version strings have well-defined structures that regex captures cleanly. The pattern verifies format; checksums and validity against a registry need additional checks.

Quick usage in different languages

This exact pattern — with the correct escaping and idioms for each language:

JavaScript: /^[0-9a-fA-F]{40}$/.test(value)
Python: re.match(r"^[0-9a-fA-F]{40}$", value)
Java: Pattern.compile("^[0-9a-fA-F]{40}$").matcher(value).matches()
C# / .NET: Regex.IsMatch(value, @"^[0-9a-fA-F]{40}$")
Go: regexp.MustCompile(`^[0-9a-fA-F]{40}$`).MatchString(value)
Ruby: /^[0-9a-fA-F]{40}$/.match?(value)
PHP: preg_match('~^[0-9a-fA-F]{40}$~', $value)

The explainer’s Code tab regenerates these for any pattern you paste, and the downloadable cheat sheet bundles the breakdown, all seven snippets, and the pitfalls below onto one printable page.

Common pitfalls

Anchored to the whole string. This pattern uses ^ and $, so it requires the entire input to match. To find it inside a longer text, drop the anchors and use the global (g) flag.
Case sensitivity. Letter ranges are case-sensitive — use the i flag if the input case can vary.
Validate beyond format. Matching the format doesn't guarantee the value is real. Confirm the sha-1 hash against a source of truth (database, API, or checksum) where it matters.

Standards & sources

This pattern is based on the following authoritative specification(s) and issuing authorities. Formats can change — always confirm against the primary source.

RFC 3174 — US Secure Hash Algorithm 1 (SHA1)

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