Pattern

Regex for Environment variable reference

$VAR or ${VAR} in shell scripts.

The Environment variable reference regex is \$\{?([A-Z_][A-Z0-9_]*)\}? — copy it below, or open it in the explainer for a token-by-token breakdown.

The pattern

\$\{?([A-Z_][A-Z0-9_]*)\}?

Try in explainer → Download cheat sheet ↓

What it matches

$HOME
${PATH}
$JAVA_HOME
${USER_NAME}

What it doesn't match

$var (lowercase)
${not closed
plaintext

Notes & gotchas

Captures the variable name in group 1. Bash convention is uppercase with underscores. Doesn't match lowercase or local variables — adjust the character class for those.

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 “$”
`\{?`	optional (zero or one): literal “{”
`(`	start of a capturing group
`[A-Z_]`	any of: uppercase letters, “_”
`[A-Z0-9_]*`	zero or more: any of: uppercase letters, digits, “_”
`)`	end of group
`\}?`	optional (zero or one): literal “}”

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-Z_][A-Z0-9_]*)\}?/.test(value)
Python: re.match(r"\$\{?([A-Z_][A-Z0-9_]*)\}?", value)
Java: Pattern.compile("\\$\\{?([A-Z_][A-Z0-9_]*)\\}?").matcher(value).matches()
C# / .NET: Regex.IsMatch(value, @"\$\{?([A-Z_][A-Z0-9_]*)\}?")
Go: regexp.MustCompile(`\$\{?([A-Z_][A-Z0-9_]*)\}?`).MatchString(value)
Ruby: /\$\{?([A-Z_][A-Z0-9_]*)\}?/.match?(value)
PHP: preg_match('~\$\{?([A-Z_][A-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.
Uppercase only. Ranges like [A-Z] won't match lowercase. Add a-z (or the i flag) if lowercase input should be accepted.
Escape it correctly per language. In Java and JavaScript strings each backslash must be doubled (\\d); in Python, Go, and C# use raw/verbatim strings so the backslashes survive.
Validate beyond format. Matching the format doesn't guarantee the value is real. Confirm the environment variable reference against a source of truth (database, API, or checksum) where it matters.

Related patterns

More patterns in the Developer category: