cat4.c

/*
    cat4.c -- simple cat command with -e option

    Copyright (c) 2017 Minero Aoki

    This program is free software.
    Redistribution and use in source and binary forms,
    with or without modification, are permitted.
*/

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>

static void do_cat(FILE *f, int escape);

int
main(int argc, char *argv[])
{
    int opt;
    int escape = 0;
    int i;

    while ((opt = getopt(argc, argv, "e")) != -1) {
        switch (opt) {
        case 'e':
            escape = 1;
            break;
        case '?':
            fprintf(stderr, "Usage: %s [-e] [file...]\n", argv[0]);
            exit(1);
        }
    }
    argc -= optind;
    argv += optind;
    if (argc == 0) {
        do_cat(stdin, escape);
    }
    else {
        for (i = 0; i < argc; i++) {
            FILE *f;

            f = fopen(argv[i], "r");
            if (!f) {
                perror(argv[i]);
                exit(1);
            }
            do_cat(f, escape);
            fclose(f);
        }
    }
    exit(0);
}

static void
do_cat(FILE *f, int escape)
{
    int c;

    if (escape) {
        while ((c = fgetc(f)) != EOF) {
            switch (c) {
            case '\t':
                if (fputs("\\t", stdout) == EOF) exit(1);
                break;
            case '\n':
                if (fputs("$\n", stdout) == EOF) exit(1);
                break;
            default:
                if (putchar(c) < 0) exit(1);
                break;
            }
        }
    }
    else {
        while ((c = fgetc(f)) != EOF) {
            if (putchar(c) < 0) exit(1);
        }
    }
}