Regex for extracting qmake variables

Question

I'm trying to write the QRegExp for extracting variable names from qmake project code (*.pro files).
The syntax of variable usage have two forms:

• $$VAR
• $${VAR}

So, my regular expression must handle both cases. I'm trying to write expression in this way:

\$\$\{?(\w+)\}?

But it does not work as expected: for string $$VAR i've got $$V match, with disabled "greeding" matching mode (QRegExp::setMinimal (true)). As i understood, gready-mode can lead to wrong results in my case.
So, what am i doing wrong?
Or maybe i just should use greedy-mode and don't care about this behavior :)

P.S. Variable name can't contains spaces and other "special" symbols, only letters.

Answer 1

You do not need to disable greedy matching. If greedy matching is disabled, the minimal match that satisfies your expression is returned. In your example, there's no need to match the AR, because $$V satisfies your expression.

So turn the minimal mode back on, and use

\$\$(\w+|\{\w+\})

This matches two dollar signs, followed by either a bunch of word characters, or by a bunch of word characters between braces. If you can trust your data not to contain any non-matching braces, your expression should work just as well.
\w is equal to [A-Za-z0-9_], so it matches all digits, all upper and lowercase alphabetical letters, and the underscore. If you want to restrict this to just the letters of the alphabet, use [A-Za-z] instead.

Since the variable names can not contain any special characters, there's no danger of matching too much, unless a variable can be followed directly by more regular characters, in which case it's undecidable.
For instance, if the data contains a string like Buy our new $$Varbuster!, where $$Var is supposed to be the variable, there is no regular expression that will separate the variable from the rest of the string.