Regular expressions (regex) are one of the most powerful tools in a developer's arsenal—and one of the most feared. This tutorial breaks down regex into digestible pieces, building from basic concepts to patterns you can use in real projects.
🎯 By the end of this tutorial, you'll be able to: Write patterns for email validation, password requirements, phone numbers, and more. You'll understand quantifiers, groups, lookaheads, and know when to use (or avoid) regex.
O que são expressões regulares?
Regular expressions are patterns that describe sets of strings. They're used to:
- Search: Find text matching a pattern
- Validate: Check if input matches expected format
- Extract: Pull specific parts from text
- Replace: Transform text based on patterns
O básico: caracteres literais
The simplest regex is just literal text:
Matches: "hello" in "hello world"
Does not match: "Hello" (case-sensitive by default)
Classes de personagens
Match any single character from a set:
| Pattern | Matches | Example |
|---|---|---|
[abc] |
a, b, or c | "cat" matches c |
[a-z] |
Any lowercase letter | "Hello" matches e, l, l, o |
[A-Z] |
Any uppercase letter | "Hello" matches H |
[0-9] |
Any digit | "abc123" matches 1, 2, 3 |
[^abc] |
NOT a, b, or c | "dog" matches d, o, g |
Classes de caracteres abreviados
| Shorthand | Equivalent | Description |
|---|---|---|
\d |
[0-9] |
Any digit |
\D |
[^0-9] |
Not a digit |
\w |
[a-zA-Z0-9_] |
Word character |
\W |
[^a-zA-Z0-9_] |
Not a word character |
\s |
[ \t\n\r] |
Whitespace |
\S |
[^ \t\n\r] |
Not whitespace |
. |
(almost anything) | Any character except newline |
Quantificadores: Quantos?
| Quantifier | Meaning | Example |
|---|---|---|
* |
0 or more | ab*c matches "ac", "abc", "abbc" |
+ |
1 or more | ab+c matches "abc", "abbc", not "ac" |
? |
0 or 1 | colou?r matches "color" and "colour" |
{n} |
Exactly n | \d{4} matches "2026" |
{n,} |
n or more | \d{2,} matches "12", "123", "1234" |
{n,m} |
Between n and m | \d{2,4} matches "12", "123", "1234" |
✅ Ganancioso vs Preguiçoso
Quantifiers are "greedy" by default—they match as much as possible. Add ? to make them
"lazy" (match as little as possible). .* vs .*?
Âncoras: onde combinar
| Anchor | Position | Example |
|---|---|---|
^ |
Start of string/line | ^Hello matches "Hello world", not "Say Hello" |
$ |
End of string/line | world$ matches "Hello world", not "world peace" |
\b |
Word boundary | \bcat\b matches "cat" but not "category" |
Grupos e captura
Parentheses create groups for:
- Applying quantifiers to multiple characters:
(ab)+ - Capturing matched text for later use
- Creating alternatives:
(cat|dog)
Exemplo: Capturando Grupos
Input: "555-123-4567"
Group 0 (full match): "555-123-4567"
Group 1: "555"
Group 2: "123"
Group 3: "4567"
Grupos sem captura
Use (?:...) when you need grouping but don't need to capture:
Padrões práticos
Validação de e-mail (básico)
Matches: [email protected], [email protected]
Número de telefone (EUA)
Matches: (555) 123-4567, 555-123-4567, 555.123.4567
Senha (8+ caracteres, maiúsculas, minúsculas, número)
Uses lookaheads to require different character types
URL
Matches: http://example.com, https://sub.domain.com/path
Olhar para frente e olhar para trás
Match based on what comes before or after, without including it in the match:
| Type | Syntax | Description |
|---|---|---|
| Positive Lookahead | (?=...) |
Followed by ... |
| Negative Lookahead | (?!...) |
NOT followed by ... |
| Positive Lookbehind | (?<=...) |
Preceded by ... |
| Negative Lookbehind | (? |
NOT preceded by ... |
foo(?=bar) // matches "foo" in "foobar", not in "foobaz"
// Match $ amount (digit preceded by $)
(?<=\$)\d+ // matches "100" in "$100"
Sinalizadores/Modificadores
| Flag | Description |
|---|---|
i |
Case-insensitive matching |
g |
Global - find all matches, not just first |
m |
Multiline - ^ and $ match line boundaries |
s |
Dotall - . matches newlines too |
Erros Comuns
- Forgetting to escape:
.,*,+,?, etc. have special meaning. Use\.to match a literal period. - Greedy matching:
.*matches too much. Use.*?for lazy matching. - Missing anchors:
\d{4}matches "2026" anywhere. Use^\d{4}$for exact match. - Overcomplicated patterns: Sometimes string methods or multiple simple patterns are clearer.
🔧 Teste seus padrões
Use our free RegEx Tester to experiment with patterns and see matches in real-time.
Abra o testador RegEx →Quando NÃO usar Regex
- Parsing HTML/XML: Use a proper parser. Regex can't handle nested tags correctly.
- Complex validation: Email RFC is incredibly complex. Use a library.
- Simple tasks:
str.includes()orstr.startsWith()are clearer than regex.
Conclusão
Regular expressions are like a superpower—incredibly useful once you learn them, but easy to misuse. Start with simple patterns, test incrementally, and don't be afraid to use comments or break complex patterns into pieces.
The key to mastering regex is practice. Use the patterns in this tutorial as building blocks, experiment with variations, and soon you'll be writing patterns confidently.