正则表达式匹配 1 次或更少出现的字符串？

Question

Suppose I want a regex to match "Jump over this bridge FOOL" as well as "Jump over this bridge". How do I make "FOOL" optional (0 or 1 occurrence)?

Answer 1

You can use the ? mark to specify the occurrence of a group as optional (occurs 0 or 1 time), or you can also use curly braces with min/max values as 0 and 1, so the answer is:

Jump over this bridge( FOOL)?

or

Jump over this bridge( FOOL){0,1}

Answer 2

You might want to have a look at a regex tutorial .

Optional parts of a regex are indicated with a question mark:

Jump over this bridge( FOOL)?

In case you want to match any string that includes FOOL less than twice, things get a bit more complicated. Then you would be best off using the more advanced concept of a negative lookahead :

^(?!(.*FOOL){2})

This turns the logic on its head and asserts that the string doesn't contain 2 (or more) instances of FOOL .

Answer 3

Try doing this :

Jump over this bridge( FOOL)?

You can put a set of strings too :

Jump over this bridge( FOOL| FOOB)?