Is this "regulated" by the author of the tool?
Yes and no. The programmer must consciously provide this in his program, but for this there is a standard library function - getopt() and the built-in shell command getopts . Both are standardized by POSIX. Interfaces to getopt are available in almost all languages.
For example, I will write a program that will work with the following arguments: -R -t -dT,
Assuming that it is -d and -T are two different keys, in C, a typical processing example would look something like this:
#include <stdbool.h> #include <stdlib.h> #include <unistd.h> void usage(const char* name) { printf(stderr, "Usage: %s" -[RtdT] [-f <file>], name); } int main (int argc, char **argv){ bool recursive=0; bool show_directory=0 bool super_time=0; char *file; int c; while ((c = getopt (argc, argv, "RtdTf:")) != -1) { switch (c) { case 'R': recursive = 1; break; case 't': process_time = 1; break; case 'd': show_directorye = 1; break; case 'T': process_time = 0; break; case 'f': file = optarg break; case 'h': usage(argv[0]); return EXIT_SUCCESS; case '?': return EXIT_FAILURE; default: assert(0); } } // do stuff return EXIT_SUCCESS; }
glibc also provides the function getopt_long () , which supports the parsing of long arguments like - --some-option and - --some-option-with-arg=val , but this is only a GNU extension.
For example, take the standard ls program, and run it with the arguments -a -l. We get a conclusion.
This behavior of most utilities, by the way, is also standardized by POSIX.
