Question

I have a command line application that needs to support arguments of the following brand:

1. all: return everything
2. search: return the first match to search
3. all*search: return everything matching search
4. X*search: return the first X matches to search
5. search#Y: return the Yth match to search

Where search can be either a single keyword or a space separated list of keywords, delimited by single quotes. Keywords are a sequence of one or more letters and digits – nothing else.

A few examples might be:

1. 2*foo
2. bar#8
3. all*’foo bar’

This sounds just complex enough that flex/bison come to mind – but the application can expect to have to parse strings like this very frequently, and I feel like (because there’s no counting involved) a fully-fledged parser would incur entirely too much overhead.

What would you recommend? A long series of string ops? A few beefy subpattern-capturing regular expressions? Is there actually a plausible argument for a “real” parser?

It might be useful to note that the syntax for this pseudo-grammar is not subject to change, so if the code turns out less-than-wonderfully-maintainable, I won’t cry. This is all in C++, if that makes a difference.

Thanks!

Answer 1

The answer mostly depends on a balance between how much coding you want to do and how much libraries you want to depend on – if your application can depend on other libraries, you can use any of the many regular expression libraries – e.g. POSIX regex which comes with all Linux/Unix flavors.

OR

If you just want those specific syntaxes, I would use the string tokenizer (strtok) – split on ‘*’ and split on ‘#’ – then handle each case.