Generating Regex Code Across Multiple Programming Languages

Writing a regex pattern is only half the work. Integrating it into code requires understanding how each language handles syntax, escaping, flags, and API conventions. A pattern that works in a regex tester may fail in code due to string escaping issues, missing flags, or API differences.

The Escaping Problem

The backslash is an escape character in both strings and regex. To match a literal backslash, the regex needs `\\`, which in some string literals becomes `"\\\\"`. Languages like Python offer raw strings (`r"\d+"`) and JavaScript offers regex literals (`/\d+/`) to avoid this double-escaping problem.

Language-Specific Syntax

JavaScript uses regex literals (`/pattern/flags`) or `new RegExp('pattern', 'flags')`. Python uses `re.compile(r'\d+')` with flag constants. Swift uses `NSRegularExpression(pattern: "\\d+")` or Swift 5.7+ regex literals. Java uses `Pattern.compile("\\d+")`. Go uses backtick raw strings: `regexp.Compile(`\d+`)`.

Translating Flags

Case-insensitive matching is `/i` in JavaScript, `re.IGNORECASE` in Python, `Pattern.CASE_INSENSITIVE` in Java. Multiline mode is `/m` in JavaScript but in Ruby `/m` enables dotAll mode instead. These inconsistencies cause cross-language bugs.

Feature Availability

Named capture groups use `(?P<name>...)` in Python but `(?<name>...)` in JavaScript. Possessive quantifiers work in Java and PCRE but not JavaScript. Unicode property escapes work in Java and modern JavaScript but require the `regex` module in Python. Verify feature support before translating.

Automating Code Generation

RegExpress includes code generation that exports tested patterns as ready-to-use snippets for multiple languages, complete with correct escaping and appropriate API calls. This eliminates escaping bugs and flag translation errors.