Lección 2
Literals and Metacharacters en español
Guía en español para regex regex literals and metacharacters: Character classes, quantifiers, anchors, and escaping.
Este contenido todavía no está disponible en español. Se muestra la versión en English mientras completamos la localización.
Most regex syntax falls into two buckets: literals (match themselves) and metacharacters (special symbols with meaning).
Literals and escaping
Letters and digits usually match themselves: cat matches the substring cat.
Metacharacters such as . * + ? [ ] ( ) { } | ^ $ \ need care:
.matches any one character (except line terminators in some modes)- To match a literal dot, escape it:
\.
When in doubt, use a character class for punctuation: [.] matches a dot without escaping debates.
Character classes
[abc] matches one character from the set a, b, or c.
Useful shorthands (JavaScript-style):
| Class | Meaning |
|---|---|
\d | Digit [0-9] |
\w | “Word” char (engine-specific; often [A-Za-z0-9_] ) |
\s | Whitespace |
\D, \W, \S | Negated versions |
Ranges: [a-z] for lowercase letters. Put - first or last if you need a literal hyphen inside a class.
Quantifiers
Repeat the previous atom:
| Quantifier | Meaning |
|---|---|
* | Zero or more |
+ | One or more |
? | Zero or one |
{3} | Exactly 3 |
{2,5} | Between 2 and 5 |
{2,} | Two or more |
Greedy vs lazy: + consumes as much as possible; +? consumes as little as possible. This matters when parsing delimited fields.
Anchors
| Anchor | Meaning (typical) |
|---|---|
^ | Start of input or line (with multiline flag) |
$ | End of input or line |
\b | Word boundary |
^https:// ensures the URL starts at the beginning (or line start), not in the middle of a sentence.
Grouping
( ... ) groups atoms so quantifiers apply to the group: (ab)+ matches ab, abab, etc.
Key takeaway
Build patterns from small tested pieces: anchor + class + quantifier. Complex patterns become readable when each segment has one job.