Single Line Comment Validation Regex

Match single-line comments starting with // that extend to the end of the line using regex pattern.

Pattern Breakdown

\/\/.*$

Components

Character Classes

• \/\/ - Literal // (both forward slashes escaped)
• .* - Any character except newline (greedy, matches to end of line)
• $ - End of line anchor

Examples

Matches:

• // This is a comment
• code(); // inline comment
• // Comment at start of line
• var x = 5; // assignment comment

Doesn't Match:

• /* This is not a single-line comment */ (multi-line syntax)
• // Comment continues (only matches first line)
• Comment without markers (no markers)

Implementation

JavaScript

const singleLineCommentRegex = /\/\/.*$/gm; // 'm' flag for multiline, 'g' for global
const code = `var x = 5; // assignment
var y = 10; // another comment`;
const comments = code.match(singleLineCommentRegex);
// ['// assignment', '// another comment']

// To remove comments
const withoutComments = code.replace(/\/\/.*$/gm, '');

Python

import re
single_line_comment_regex = r'//.*$'
code = """var x = 5; // assignment
var y = 10; // another comment"""
comments = re.findall(single_line_comment_regex, code, re.MULTILINE)
# ['// assignment', '// another comment']

# To remove comments
without_comments = re.sub(single_line_comment_regex, '', code, flags=re.MULTILINE)

Go

import "regexp"
singleLineCommentRegex := regexp.MustCompile(`(?m)//.*$`) // (?m) for multiline mode
code := "var x = 5; // assignment\nvar y = 10; // another comment"
comments := singleLineCommentRegex.FindAllString(code, -1)
// ["// assignment", "// another comment"]

// To remove comments
withoutComments := singleLineCommentRegex.ReplaceAllString(code, "")

Limitations

1. No string handling: May match // inside strings (e.g., "http://example.com")
2. End of line only: Only matches comments at end of line
3. No multi-line: Doesn't handle comments spanning multiple lines
4. Language specific: Works for languages that use // (JavaScript, C++, Java, etc.)
5. No escape sequences: Doesn't account for escaped characters

When to Use

• Extracting single-line comments
• Removing comments from code
• Code minification
• Comment validation in supported languages
• Quick comment matching

For production, consider:

• Handling // inside strings properly
• Using proper parsers for language-specific comment handling
• Supporting different comment styles if needed
• Preserving comments in minification if required
• Using AST parsers for accurate comment extraction