Pattern

Regex for Positive integer

Non-negative whole number, no leading zeros.

The Positive integer regex is ^(0|[1-9]\d*)$ — copy it below, or open it in the explainer for a token-by-token breakdown.

The pattern

^(0|[1-9]\d*)$

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What it matches

0
1
42
1000000

What it doesn't match

-1
01
1.5
1e2
abc

Notes & gotchas

Zero is allowed; leading zeros are not (so "007" fails). For values where leading zeros matter (codes, IDs), use a different pattern.

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)
`(`	start of a capturing group
`0`	literal text “0”
`\|`	OR — try the alternative
`[1-9]`	any of: 1–9
`\d*`	zero or more: digit (0–9)
`)`	end of group
`$`	end of string (or line in multiline mode)

About this pattern

Number patterns appear constantly in form validation, log parsing, and data extraction. Regex is great for matching the shape but limited for semantic checks (range validation, mathematical constraints).

Quick usage in different languages

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

JavaScript: /^(0|[1-9]\d*)$/.test(value)
Python: re.match(r"^(0|[1-9]\d*)$", value)
Java: Pattern.compile("^(0|[1-9]\\d*)$").matcher(value).matches()
C# / .NET: Regex.IsMatch(value, @"^(0|[1-9]\d*)$")
Go: regexp.MustCompile(`^(0|[1-9]\d*)$`).MatchString(value)
Ruby: /^(0|[1-9]\d*)$/.match?(value)
PHP: preg_match('~^(0|[1-9]\d*)$~', $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.
Escape it correctly per language. In Java and JavaScript strings each backslash must be doubled (\\d); in Python, Go, and C# use raw/verbatim strings so the backslashes survive.
Validate beyond format. Matching the format doesn't guarantee the value is real. Confirm the positive integer against a source of truth (database, API, or checksum) where it matters.

Related patterns

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