grep.c

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

#define MAXLINE 1000

int _getline(char *, int);

int main(int argc, char *argv[]) {
    char line[MAXLINE];
    long lineno = 0;
    int c, except = 0, number = 0, found = 0;
    while (--argc > 0 && (*++argv)[0] == '-')
        while ((c = *++argv[0]))
            switch (c) {
                case 'x':
                    except = 1;
                    break;
                case 'n':
                    number = 1;
                    break;
                default:
                    printf("illegal option %c\n", c);
                    argc = 0;
                    found = -1;
                    break;
            }
    if (argc != 1)
        printf("Usage: ./a.out -x -n PATTERN\n");
    else
        while (_getline(line, MAXLINE) > 0) {
            lineno++;
            if ((strstr(line, *argv) != NULL) != except) {
                if (number)
                    printf("%ld:", lineno);
                printf("%s", line);
                found++;
            }
        }
    return found;
}

int _getline(char *s, int n)
{
    int c;
    char *tmp = s;
    while(n-- > 0 && (c = getchar()) != EOF && c != '\n')
        *s++ = c;
    if (c == '\n')
        *s++ = c;
    *s = '\0';
    return s - tmp;
}