Space or no space

"space or no space" is the same as "zero or one space", or perhaps "zero or more spaces", I'm not sure exactly what you want.

In the following discussion, I'm going to use <space> to represent a single space, since a single space is hard to see in short code snippets. In the actual regular expression, you must use an actual space character.

zero-or-one-space is represented as a single space followed by a question mark (<space>?). That will match exactly zero or one spaces. If you want to match zero or any number of spaces, replace the ? with * (eg: <space>*)

If by "space" you actually mean "any whitespace character" (for example, a tab), you can use \s which most regular expression engines translate as whitespace. So, zero-or-one of any whitespace character would be \s?, and zero-or-more would be \s*

Other alternatives for the space or no-space problem (notice the spaces at the beginning in some):

[ ]{0,1}
 {0,1}
[ ]?
 ?