usr/rev.c


1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43

#include "gbos.h"
/* rev [file]: reverse the characters of each line, from a file or stdin. */

#define MAXLINE 80

void main(void) {
    char *argv[4];
    char line[MAXLINE];
    unsigned char argc = argv_parse(argv, 4);
    unsigned char len = 0, fd = NOFD, i;
    int ch;

    if (argc > 0 && argv[0][0] != '-') {
        fd = open(argv[0], O_READ);
        if (fd == EISDIR) {
            puts("rev: is a directory");
            nl();
            sexit(2);
        }
        if (fd == NOFD) {
            puts("rev: no such file");
            nl();
            sexit(2);
        }
    }
    for (;;) {
        if (fd == NOFD) {
            char c = readc();
            ch = (c == EOF) ? -1 : c;
        } else ch = fgetc(fd);
        if (ch == '\r') continue;
        if (ch >= 0 && ch != '\n') {
            if (len < MAXLINE) line[len++] = (char)ch;
            continue;
        }
        if (ch < 0 && len == 0) break;
        for (i = len; i--;) putc(line[i]);
        nl();
        len = 0;
        if (ch < 0) break;
    }
    if (fd != NOFD) close(fd);
}