Question

I am trying to understand how grep works.

When I say grep "hello" *.*, does grep get 2 arguments — (1) string to be searched i.e. “hello” and (2) path *.*? Or does the shell convert *.* into something that grep can understand?

Where can I get source code of grep? I came across this GNU grep link. One of the README files says its different from unix grep. How so?

I want to look at source of FreeBSD version of grep and also Linux version of it (if they are different).

Answer 1

The shell does the globbing (conversion from * form to filenames). You can see this by if you have a simple C program:

#include <stdio.h>

int main(int argc, char **argv) {
    for(int i=1; i<argc; i++) {
        printf("%s\n", argv[i]);
    }
    return 0;
}

And then run it like this:

./print_args *

You’ll see it prints out what matched, not * literally. If you invoke it like this:

./print_args '*'

You’ll see it gets a literal *.