Question

Ok, a friend of mine confronted me with a regular expression he found in a piece of code and I am not experienced at all. I tried to figure it out and I really think that it is quite basic, but I have trouble.

The expression is: ^(.*?){0,1}>$

So this is what I gathered from various tutorials and definitions:

• ^ stands for “start” and $ for end, so expression between those must describe the full string in order to be selected.
• *? is a lazy operator (meaning it first tries to take 0 of the preceeding character, if that doesn’t match, it takes one, two, three, etc).
• (.*?) so this must mean “takes as few characters as possible”.
• (.*?){0,1}: Now the trouble beginns for me. “Take as few characters as possible, zero times or once”?
• ^(.*?){0,1}>$: “Take as few characters as possible, zero times or once, with the character > afterwards followed by the end”?

That would basically mean “select everything, if a > is at the end of the string”? I am confused… I would appreciate it if someone could shed some light on this (I guess very basic) problem…

EDIT: Ok, to prevent missunderstanding, the regex is used in this context:

.replace(/^(.*?){0,1}>$/,"$1/>");

Answer 1

What you have is equivalent to the following:

^(.*)>$

Whoever wrote it in the first place was probably in a hurry, and didn’t realize they were putting so much extraneous stuff in there.

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After clarifying your use case, just use this:

.replace(/>$/, '/>');

and it’ll add a slash before the closing > tag (if there is one).

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If you want to add the slash only if it’s not there yet, use this:

.replace(/([^\/])>$/, '$1/>');