Difference between * and + regex

Question

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

[<>]+ [<>]*

Answer 1

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

Answer 2

* 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.

Answer 3

+ 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.

Answer 4

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)

Answer 5

* 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.

Answer 6

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