Pattern

Regex for Line comment (// or #)

Single-line comment in C-family or scripting languages.

The Line comment (// or #) regex is (\/\/|#).*$ — copy it below, or open it in the explainer for a token-by-token breakdown.

The pattern

(\/\/|#).*$

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What it matches

// JS comment
# Python comment
// rest of line

What it doesn't match

code only
/* not a line comment */

Notes & gotchas

Use the /m flag for multiline mode so $ matches at line boundaries. Won't correctly handle // inside strings — for that, use a real lexer.

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 a capturing group
`\/`	literal “/”
`\/`	literal “/”
`\|`	OR — try the alternative
`#`	literal text “#”
`)`	end of group
`.*`	zero or more of any character
`$`	end of string (or line in multiline mode)

About this pattern

Developer-oriented patterns help with code analysis, log parsing, and data transformation. Use these in build scripts, CI tools, and code review utilities.

Quick usage in different languages

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

JavaScript: /(\\/\\/|#).*$/.test(value)
Python: re.match(r"(\/\/|#).*$", value)
Java: Pattern.compile("(\\/\\/|#).*$").matcher(value).matches()
C# / .NET: Regex.IsMatch(value, @"(\/\/|#).*$")
Go: regexp.MustCompile(`(\/\/|#).*$`).MatchString(value)
Ruby: /(\\/\\/|#).*$/.match?(value)
PHP: preg_match('~(\/\/|#).*$~', $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 $, so it requires the entire input to match. To find it inside a longer text, drop the anchors and use the global (g) flag.
Greedy “.*”. A greedy .* / .+ can match more than intended. Use a lazy version (.*?) or a negated class ([^…]) to stop at the right place.
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 line comment (// or #) against a source of truth (database, API, or checksum) where it matters.

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