CODEWITHSUNDEEP
regex
Few Tem
Few Tem

Reputation: 673

Difference between * and + regex

Can anybody tell me the difference between the * and + operators in the example below:

[<>]+ [<>]*

Upvotes: 34

Views: 35810

Answers (7)

godot
godot

Reputation: 3545

I'll bring some example to extend answers above. Let we have a text:

100test10
test10
test

if we write \d+test\d+, this expression matches 100test10 and test10 but \d*test\d* matches three of them

Upvotes: 2

ghoti
ghoti

Reputation: 46836

+ means one or more of the previous atom. ({1,})

* means zero or more. This can match nothing, in addition to the characters specified in your square-bracket expression. ({0,})

Note that + is available in Extended and Perl-Compatible Regular Expressions, and is not available in Basic RE. * is available in all three RE dialects. That dialect you're using depends most likely on the language you're in.

Pretty much, the only things in modern operating systems that still default to BRE are grep and sed (both of which have ERE capability as an option) and non-vim vi.

Upvotes: 8

dan radu
dan radu

Reputation: 2782

They are quantifiers.

  • + means 1 or many (at least one occurrence for the match to succeed)
  • * means 0 or many (the match succeeds regardless of the presence of the search string)

Upvotes: 5

aleroot
aleroot

Reputation: 72636

Each of them are quantifiers, the star quantifier(*) means that the preceding expression can match zero or more times it is like {0,} while the plus quantifier(+) indicate that the preceding expression MUST match at least one time or multiple times and it is the same as {1,} .

So to recap : 

a*  ---> a{0,}  ---> Match a or aa or aaaaa or an empty string
a+  ---> a{1,}  ---> Match a or aa or aaaa but not a string empty

Upvotes: 64

detale
detale

Reputation: 12892

[<>]+ is same as [<>][<>]*

Upvotes: 3

jahroy
jahroy

Reputation: 22692

* means zero or more of the previous expression.

In other words, the expression is optional.

You might define an integer like this:

-*[0-9]+

In other words, an optional negative sign followed by one or more digits.

Upvotes: 5

Ismail Badawi
Ismail Badawi

Reputation: 37177

* means zero-or-more, and + means one-or-more. So the difference is that the empty string would match the second expression but not the first.

Upvotes: 14

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