Regular Expression - Match End if Start is Match

Question

I want to match the following strings:

[anything can be here]
[{anything can be here}]

Can I achieve this using only one regular expression?

I am currently using this one '^\[({)?.+(})?]$', but it will match also:

[anything can be here}]
[{anything can be here]

I need to to match } only if { is used.

Please, note I can use only regular expression match function as I have implemented it as SQL CLR function in order to use it in T-SQL statements.

Answer 1

Basically you can write (verbatim strings):

^\[(?:{.+}|[^]{}]+)]$

You can use something more complicated with a conditional statement (?(condition)then|else):

^\[({)?[^]{}]+(?(1)}|)]$

(if capture group 1 exists, then } else nothing)

But this way is probably less efficient.

Answer 2

I got this working: \[[^{].*[^}]\]|\[\{.*\}\]

EDIT as pointed out by OP something needs to be between parentheses so a 'one or more' match is more suited:

\[[^{].+[^}]\]|\[\{.+\}\]

see RegEx example here

Answer 3

Your regex ^\[({)?.+(})?]$ will match only an individual string like [{...}] or [{...] because 1) you have anchors (^$), and both curly braces are present in the same pattern.

I suggest using negative look-behinds to avoid matching strings that have just 1 curly brace inside the []-ed string like this:

var rgx = new Regex(@"((?!\[\{[^}]+\]|\[[^{]+\})\[\{?.+?\}?\])");
var tst = "[anything can be here] [{anything can be here}] [anything can be here}] [{anything can be here]";
var mtch = rgx.Matches(tst).Cast<Match>().ToList();

This will make sure you match the []-ed strings even in larger context.

Result: