Multiple Line Comment Validation Regex

Match multi-line comments using /* */ syntax that can span multiple lines using regex pattern.

Pattern Breakdown

\/\*[\s\S]*?\*\/

Components

Character Classes

• \/\* - Literal /* (forward slash and asterisk, both escaped)
• [\s\S] - Any character: \s (whitespace) OR \S (non-whitespace) = matches everything including newlines
• *? - Non-greedy quantifier: matches as few characters as possible
• \*\/ - Literal */ (asterisk and forward slash, both escaped)

Examples

Matches:

• /* This is a comment */
• /* Multi-line comment */
• /* Comment spanning multiple lines */
• /* */ (empty comment)

Doesn't Match:

• // This is not a multi-line comment (single-line syntax)
• /* Unclosed comment (missing closing)
• Comment without markers (no markers)

Implementation

JavaScript

const multiLineCommentRegex = /\/\*[\s\S]*?\*\//g; // 'g' flag for global
const code = `/* First comment */
code here
/* Second
   multi-line comment */`;
const comments = code.match(multiLineCommentRegex);
// ['/* First comment */', '/* Second\n   multi-line comment */']

// To remove comments
const withoutComments = code.replace(/\/\*[\s\S]*?\*\//g, '');

Python

import re
multi_line_comment_regex = r'/\*[\s\S]*?\*/'
code = """/* First comment */
code here
/* Second
   multi-line comment */"""
comments = re.findall(multi_line_comment_regex, code)
# ['/* First comment */', '/* Second\n   multi-line comment */']

# To remove comments
without_comments = re.sub(multi_line_comment_regex, '', code)

Go

import "regexp"
multiLineCommentRegex := regexp.MustCompile(`/\*[\s\S]*?\*/`)
code := "/* First comment */\ncode here\n/* Second\n   multi-line comment */"
comments := multiLineCommentRegex.FindAllString(code, -1)
// ["/* First comment */", "/* Second\n   multi-line comment */"]

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

Limitations

1. No nested comments: Doesn't handle nested /* */ comments properly
2. Non-greedy matching: *? may not match all comments in some edge cases
3. No validation: Only matches format, doesn't validate comment syntax
4. Global flag needed: Requires global flag to find all comments
5. Performance: Can be slow with very large files

When to Use

• Extracting multi-line comments
• Removing comments from code
• Code minification
• Comment validation in C-style languages
• Processing source code files

For production, consider:

• Handling edge cases with nested comments
• Using proper parsers for language-specific comment handling
• Tracking comment positions for source maps
• Preserving comments in minification if needed
• Using AST parsers for accurate comment extraction