Regex

Regex (Regular Expressions) is a powerful search-and-replace language. Instead of searching for a specific word, you describe the shape of the text you're looking for.

The Literal & The Wildcard

abc : Matches exactly "abc".
. (dot) : Matches any single character (except a newline).
    Example: h.t matches "hat", "hit", or "h0t".

Character Classes (The "Any Of" Box)

[aeiou] : Matches any one vowel.
[a-z] : Matches any lowercase letter.
[0-9] : Matches any single digit.
[^0-9] : Matches anything except a digit.

Quantifiers (How Many?)

These follow a character to tell you how many times it repeats:

* : 0 or more times.
+ : 1 or more times.
? : 0 or 1 time (makes it optional).
{3} : Exactly 3 times.
{2,5} : Between 2 and 5 times.

Anchors (Where?)

^ : The start of a line.
$ : The end of a line.
    Example: ^Error only finds "Error" if it's the first word on the line.

Shorthand Escapes

\d : Any digit (same as [0-9]).
\w : Any "word" character (letters, numbers, underscores).
\s : Any whitespace (space, tab, newline).
\b : A word boundary (helps you find "cat" but not "catastrophe").

Examples

Look at this pattern: ^\d{3}-\d{4}$

^ : Start at the beginning of the line.
\d{3} : Find exactly 3 digits.
- : Find a literal hyphen.
\d{4} : Find exactly 4 digits.
$ : Must be the end of the line.

Result: It matches a phone number format like 555-1234.

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