how to check if there's a string in the command line

Question

I have this command line:> write_strings "Hello World!" a.txt b.txt dir/a.txt. all the elements (command, string, file names) go into an array of char pointer. how can I take an element and check if it's a string or a file name? I don't mean the exact code lines, buts just need the idea. the program should return an error if there's no string.

Answer 1

You can use an API such as stat or access to check if the file pointed to by a path exists. There is no fundamental distinction between filepaths and regular strings when they are passed to your process.

If you're using the standard main(int argc, char *argv[]) convention, you can loop through argv , checking each one to see if it's a file via one of the previously-mentioned system calls.

Answer 2

Every string that can be passed on a command line is a potential pathname, since the only restriction in both cases is that there can't be any NULs.

A program with a command line syntax in which a specific argument might or might not be used as a pathname (depending on some vague definition of "filename-ish strings" or even a file existence test) is a bad design. Each argument should have a meaning defined by its order in the argument list, or by being associated with an option like -m msg or -o outputfile .

A well-behaved unix program will let the user create a file called Hello world! if he wants.

Answer 3

not regarding how meaningful the program might or might not be - you can compare the single characters of your char *argv[] by looping through them via argv[i][j] . If every string includes a ".txt" you do not have a string, which is not a filename in your context