Quantifiers
Learn to specify repetition with *, +, ? and {}.
Quantifiers: *, +, ?, {n}
A quantifier tells how many times an item repeats. The four most common ones:
* zero or more. The pattern ab*c matches ac, abc, abbbbc.
+ one or more. ab+c requires at least one b, so it does not match ac.
? zero or one (optional). ab?c matches both ac and abc.
{n,m} between n and m repetitions. a{2,4} means 2 to 4 as.
Greedy and lazy matching
Quantifiers are greedy by default: they take the longest possible match. The pattern /".+"/ takes all text between the first and the last quote as a single piece.
You can make them lazy by adding a question mark: /".+?"/ takes the shortest match, i.e. the first "..." pair.
When extracting content between quotes or tags, lazy matching is usually safer.
Exercise Validate a phone format
Write isPhoneNumber(string $str): bool. Validate the 05XX XXX XX XX format with the pattern /^05\d{2}\s\d{3}\s\d{2}\s\d{2}$/; return true on match, false otherwise. Compare the preg_match result with === 1. The three echo calls below are already written.
Show example solution
bool { return preg_match("/^05\d{2}\s\d{3}\s\d{2}\s\d{2}$/", $str) === 1; }
Example solution:
<?php
// isPhoneNumber: validate 05XX XXX XX XX format with quantifiers
// Define the isPhoneNumber function
function isPhoneNumber(string $str): bool {
return preg_match("/^05\d{2}\s\d{3}\s\d{2}\s\d{2}$/", $str) === 1;
}
echo isPhoneNumber("0555 123 45 67") ? "valid\n" : "invalid\n";
echo isPhoneNumber("12345") ? "valid\n" : "invalid\n";
echo isPhoneNumber("0555 123 45 6") ? "valid\n" : "invalid\n";Test yourself
-
One or more digits
$pattern = "/\d____/"; preg_match($pattern, "Tel: 0555", $matches);Show answer
$pattern = "/\d+/"; preg_match($pattern, "Tel: 0555", $matches); -
Quantifier meanings
- *
- Zero or more
- +
- One or more
- ?
- Zero or one
- {2,4}
- Between two and four
-
In the pattern a*b, what does * mean?
- Exactly one 'a'
- At least one 'a'
- Zero or more 'a's
- Zero or one 'a'
Show answer
Zero or more 'a's — Correct. * means zero or more repetitions.