command line utility to copy and cat files

copy.c2

module copy;

import stdio local;
import stdlib local;

type Opts struct {
    char* from;
    char* to;
}

fn Opts parseOpts(i32 argc, char** argv) {
    Opts opts;

    shiftArgs(&argc, &argv);

    opts.from = shiftArgs(&argc, &argv);
    opts.to = shiftArgs(&argc, &argv);

    return opts;
}

fn char* shiftArgs(i32* argc, char*** argv) {
    if (*argc == 0) return nil;

    char* result = (*argv)[0];

    *argv += 1;
    *argc -= 1;

    return result;
}

fn void copyFileFromOpts(Opts opts) {
    FILE* from = stdin;
    if (opts.from) {
        from = fopen(opts.from, "rb");
        if (from == nil) {
            fatalError("file `from` cannot be read\n");
        }
    }

    FILE* to = stdout;
    if (opts.to) {
        to = fopen(opts.to, "wb");
        if (to == nil) {
            fatalError("file `to` cannot be written\n");
        }
    }

    copyFile(from, to);

    if (opts.from) {
        fclose(from);
    }

    if (opts.to) {
        fclose(to);
    }
}

fn void copyFile(FILE* from, FILE* to) {
    static char[16384] buffer;

    while (true) {
        usize bytesRead = fread(buffer, sizeof(buffer[0]), elemsof(buffer), from);
        if (bytesRead == 0) break;

        fwrite(buffer, sizeof(buffer[0]), bytesRead, to);
    }
}

fn void fatalError(const char* message) {
    fputs(message, stderr);
    exit(EXIT_FAILURE);
}

public fn i32 main(i32 argc, char** argv) {
    Opts opts = parseOpts(argc, argv);
    copyFileFromOpts(opts);
    return 0;
}