mycat.c

#include <stdio.h>
#include <getopt.h>
#include <stdlib.h>
#include <string.h>

struct flags
{
    int b, e, n, s, t, u, v;
} f = {0};

enum states
{
    new_line,
    wait4content,
    content,
};

int line_num = 0;
void println()
{
    if (f.b)
    {
        if (f.e)
        {
            printf("      \t");
        }
    }
    else if (f.n)
    {
        printf("%6d\t", ++line_num);
    }
    if (f.e)
    {
        printf("$");
    }
    printf("\n");
}

int main(int argc, char **argv)
{
    char c;

    while ((c = getopt(argc, argv, "benstvET")) != -1)
    {
        switch (c)
        {
        case 'b':
            f.b = 1;
            break;
        case 'n':
            f.n = 1;
            break;
        case 's':
            f.s = 1;
            break;
        case 'e':
            f.e = 1;
            f.v = 1;
            break;
        case 't':
            f.t = 1;
            f.v = 1;
            break;
        case 'v':
            f.v = 1;
            break;
        case 'E':
            f.e = 1;
            break;
        case 'T':
            f.t = 1;
            break;
        default:
            exit(1);
        }
    }

    for (int argind = optind; argind < argc; ++argind)
    {
        char const *infile = "-";
        if (argind < argc)
            infile = argv[argind];

        FILE *fptr;
        if ((strcmp((infile), ("-")) == 0))
        {
            fptr = freopen(NULL, "r", stdin);
        }
        else
        {
            fptr = fopen(infile, "r");
        }
        if (fptr == NULL)
        {
            // printf("mycat: cannot open file: %s\n", infile);
            exit(1);
        }

        int state = new_line;
        while ((c = getc(fptr)) != EOF)
        {
            if (state == wait4content)
            { // s
                if (c == '\n')
                    continue;
                else
                {
                    println();
                    state = new_line;
                }
            }
            if (state == new_line)
            {
                if (c == '\n')
                {
                    if (f.s)
                    {
                        state = wait4content;
                        continue;
                    }
                    println();
                }
                else
                {
                    if (f.b || f.n)
                    {
                        printf("%6d\t", ++line_num);
                    }
                    state = content;
                }
            }
            if (state == content)
            {
                if (c == '\n')
                {
                    if (f.e)
                    {
                        printf("$");
                    }
                    printf("\n");
                    state = new_line;
                    continue;
                }
                else
                {
                    int nonPrintable = (c >= 0 && c < 32) || (c == 127);

                    if (c == '\t')
                    {
                        if (f.t)
                        {
                            printf("^I");
                        }
                        else
                        {
                            printf("\t");
                        }
                    }
                    else if (f.v && nonPrintable)
                    {
                        if (c == 127)
                        {
                            printf("^?");
                        }
                        else
                        {
                            printf("^%c", c + 64);
                        }
                    }
                    else
                    {
                        printf("%c", c);
                    }
                }
            }
        }
        if (state == wait4content)
        {
            println();
        }
        fclose(fptr);
    }
}