Pattern

Regex for Windows environment variable

%VAR% style Windows environment variable.

The Windows environment variable regex is %([A-Za-z_][A-Za-z0-9_]*)% — copy it below, or open it in the explainer for a token-by-token breakdown.

The pattern

%([A-Za-z_][A-Za-z0-9_]*)%

Try in explainer → Download cheat sheet ↓

What it matches

%USERPROFILE%
%PATH%
%TEMP%
%APPDATA%

What it doesn't match

%not closed
$HOME
%123BAD%

Notes & gotchas

Windows cmd-style variable reference. Group 1 captures the name. PowerShell uses $env:VAR syntax instead.

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.

Open in explainer →

Token-by-token breakdown

Every part of the pattern, left to right:

Token	Meaning
`%`	literal text “%”
`(`	start of a capturing group
`[A-Za-z_]`	any of: uppercase letters, lowercase letters, “_”
`[A-Za-z0-9_]*`	zero or more: any of: uppercase letters, lowercase letters, digits, “_”
`)`	end of group
`%`	literal text “%”

About this pattern

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

Quick usage in different languages

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

JavaScript: /%([A-Za-z_][A-Za-z0-9_]*)%/.test(value)
Python: re.match(r"%([A-Za-z_][A-Za-z0-9_]*)%", value)
Java: Pattern.compile("%([A-Za-z_][A-Za-z0-9_]*)%").matcher(value).matches()
C# / .NET: Regex.IsMatch(value, @"%([A-Za-z_][A-Za-z0-9_]*)%")
Go: regexp.MustCompile(`%([A-Za-z_][A-Za-z0-9_]*)%`).MatchString(value)
Ruby: /%([A-Za-z_][A-Za-z0-9_]*)%/.match?(value)
PHP: preg_match('~%([A-Za-z_][A-Za-z0-9_]*)%~', $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

Not anchored. Without ^ and $ this can match a substring anywhere in the input — add anchors if you need the whole value to conform.
ASCII letters only. [a-zA-Z] excludes accented and non-Latin letters (é, ü, ß, ñ, and non-Latin scripts). For international input use Unicode properties like \p{L} with the u flag.
Validate beyond format. Matching the format doesn't guarantee the value is real. Confirm the windows environment variable against a source of truth (database, API, or checksum) where it matters.

Related patterns

More patterns in the Developer category: