Q: What are the most common string replacement use cases for developers?

Common operations: replace all newlines with \n for JSON; strip HTML tags ( ]*>); normalize whitespace (\s+ → single space); convert camelCase to snake_case (([A-Z]) → _$1, then lowercase); redact sensitive fields ("password":"[^"]*" → "password":"[REDACTED]"); replace environment-specific URLs; bulk-rename variables in a code snippet; convert Windows CRLF line endings to Unix LF (\r\n → \n).

Question 1

What is the difference between simple string replace and regex replace?

Accepted Answer

Simple (literal) replace finds an exact sequence of characters and replaces it. It is fast and predictable but cannot match patterns. Regex replace uses a regular expression to match patterns — replacing all email addresses, extracting numbers, or normalizing whitespace. In JavaScript: str.replace('foo', 'bar') replaces only the first occurrence; str.replaceAll('foo', 'bar') replaces all; str.replace(/foo/g, 'bar') uses regex with the global flag to replace all matches.

Question 2

How do I use capture groups in regex replacement?

Accepted Answer

Capture groups let you reuse matched text in the replacement. In JavaScript: 'John Smith'.replace(/(\w+) (\w+)/, '$2, $1') → 'Smith, John'. $1 refers to the first group, $2 to the second. Named groups: /(?\w+) (?\w+)/ → replacement '$, $'. In Python: re.sub(r'(\w+) (\w+)', r'\2, \1', 'John Smith'). Capture groups are essential for reformatting dates, phone numbers, and structured text patterns.

Question 3

What are the most common string replacement use cases for developers?

Accepted Answer

Common operations: replace all newlines with 
 for JSON; strip HTML tags (<[^>]*>); normalize whitespace (\s+ → single space); convert camelCase to snake_case (([A-Z]) → _$1, then lowercase); redact sensitive fields ("password":"[^"]*" → "password":"[REDACTED]"); replace environment-specific URLs; bulk-rename variables in a code snippet; convert Windows CRLF line endings to Unix LF (
 → 
).

Question 4

What is the difference between case-sensitive and case-insensitive replacement?

Accepted Answer

Case-sensitive replacement matches only the exact case: replacing 'foo' will not match 'Foo' or 'FOO'. Case-insensitive replacement matches any case variant: replacing 'foo' with /foo/gi (regex) or the tool's case-insensitive option matches 'foo', 'Foo', 'FOO', 'FoO'. The replacement text is used verbatim — it does not inherit the original case. For case-preserving replace (keeping original capitalization), you need a more complex regex with capture groups or a programmatic solution.

無料のWeb開発者向けツール

文字列置換

設定

検索と置換

入力

出力

文字列置換ツールの仕組み

このツールでできること

開発者によくある利用シーン

主な機能

データ形式、型、またはバリエーション

よくある落とし穴とエッジケース

コードではなくこのツールを使うべき場面