Pattern
Regex for Australian postcode
4-digit Australian postcode.
The pattern
^\d{4}$
Open in explainer →
About this pattern
Country-specific identifier formats vary widely. The pattern below validates structure; many real IDs include checksums that regex can't verify alone.
Quick usage in different languages
Once you've validated a candidate value matches this pattern, you'll typically use it inside your application code. Each language has its own regex syntax:
- JavaScript:
new RegExp(pattern).test(value) - Python:
re.match(pattern, value)with raw strings:r"pattern" - Java:
Pattern.compile(pattern).matcher(value).matches() - C# / .NET:
Regex.IsMatch(value, pattern) - Go:
regexp.MustCompile(pattern).MatchString(value)— Go uses RE2 so some advanced features aren't available - Ruby:
value =~ /pattern/orpattern.match?(value) - PHP:
preg_match('/pattern/', $value)
The explainer's Code tab generates these for any pattern you paste — including the right escaping and idioms for each language.
Common pitfalls
- Anchors matter. If the pattern uses
^and$it expects the entire input to match. To find this pattern inside a longer text, remove the anchors and use the/gflag. - Case sensitivity. Letter ranges like
[A-Z]only match uppercase. Use theiflag or[A-Za-z]for case-insensitive matching. - Escape user input. If you're building a regex from a string variable, escape regex metacharacters first to avoid bugs or injection.
- Performance. For this specific pattern the risk is low, but be cautious of nested quantifiers when adapting it — they can cause exponential backtracking on adversarial input.
See also
Browse all 300 patterns in the library, or open this regex in the interactive explainer for a token-by-token breakdown, live testing, and code in seven languages.
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