Controlling shell command line wildcard expansion in C or C++
- by Adrian McCarthy
I'm writing a program, foo, in C++. It's typically invoked on the command line like this:
foo *.txt
My main() receives the arguments in the normal way. On many systems, argv[1] is literally *.txt, and I have to call system routines to do the wildcard expansion. On Unix systems, however, the shell expands the wildcard before invoking my program, and all of the matching filenames will be in argv.
Suppose I wanted to add a switch to foo that causes it to recurse into subdirectories.
foo -a *.txt
would process all text files in the current directory and all of its subdirectories.
I don't see how this is done, since, by the time my program gets a chance to see the -a, then shell has already done the expansion and the user's *.txt input is lost. Yet there are common Unix programs that work this way. How do they do it?
In Unix land, how can I control the wildcard expansion?
(Recursing through subdirectories is just one example. Ideally, I'm trying to understand the general solution to controlling the wildcard expansion.)
