validating space in alphanumeric string thru regular expression

I am using the following regular expression

"[a-zA-Z0-9 \s]{4,}" 

to validate an alphanumeric entry with space and minimum length 4. but it doesn't accept spaces. what a开发者_运维知识库m i missing here.

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This reference over here, under flag options says:

x If set, allow use of white space and #comments within patterns

It sounds like you need to set this x flag option for whitespace to work. If I understand it correctly, your regex should look something like

"(?x)[a-zA-Z0-9 \s]{4,}"