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
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
|
#include <stdbool.h>
#include <stdio.h>
#include <string.h>
#include <syscall.h>
static void read_line (char line[], size_t);
static bool backspace (char **pos, char line[]);
int
main (void)
{
printf ("Shell starting...\n");
for (;;)
{
char command[80];
/* Read command. */
printf ("--");
read_line (command, sizeof command);
/* Execute command. */
if (!strcmp (command, "exit"))
break;
else if (!memcmp (command, "cd ", 3))
{
if (!chdir (command + 3))
printf ("\"%s\": chdir failed\n", command + 3);
}
else if (command[0] == '\0')
{
/* Empty command. */
}
else
{
pid_t pid = exec (command);
if (pid != PID_ERROR)
printf ("\"%s\": exit code %d\n", command, wait (pid));
else
printf ("exec failed\n");
}
}
printf ("Shell exiting.");
return EXIT_SUCCESS;
}
/* Reads a line of input from the user into LINE, which has room
for SIZE bytes. Handles backspace and Ctrl+U in the ways
expected by Unix users. On return, LINE will always be
null-terminated and will not end in a new-line character. */
static void
read_line (char line[], size_t size)
{
char *pos = line;
for (;;)
{
char c;
read (STDIN_FILENO, &c, 1);
switch (c)
{
case '\r':
*pos = '\0';
putchar ('\n');
return;
case '\b':
backspace (&pos, line);
break;
case ('U' - 'A') + 1: /* Ctrl+U. */
while (backspace (&pos, line))
continue;
break;
default:
/* Add character to line. */
if (pos < line + size - 1)
{
putchar (c);
*pos++ = c;
}
break;
}
}
}
/* If *POS is past the beginning of LINE, backs up one character
position. Returns true if successful, false if nothing was
done. */
static bool
backspace (char **pos, char line[])
{
if (*pos > line)
{
/* Back up cursor, overwrite character, back up
again. */
printf ("\b \b");
(*pos)--;
return true;
}
else
return false;
}
|
