blob: 9448d5ccc2b602bf08cb07f31de24ff298de3476 (
plain)
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
|
ans =
1.
-->exec('Example10.sci')
-->clear
-->flag=1
flag =
1.
-->mode(-1)
Current date is 23-Jun-2013
Welcome to the Textbook Companionship Project 2013
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Book Title : UNIX CONCEPTS AND APPLICATIONS
Book Edition : 4
Book Author : Sumitabha Das
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Code Author : Pranav Bhat T
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Chapter Number : 24
Chapter Title : Systems programming II- Files
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Example 10 : Show the effect of using dup command to achieve both input and output redirection
****************************************************************
Answer :
INSTRUCTIONS :
1.These programs are part of systems programming PURELY in Unix and the commands have NO EQUIVALENT IN SCILAB
2.However the .c files which are displayed here are also made into a seperate file.If you are a unix user then try compiling and
running the programme with gcc or cc compiler
3.The outputs displayed here are just MOCK OUTPUTS which are DISPLAYED IN THE TEXTBOOK
4.The inconvenience is regretted.
.............Press [ENTER] to continue..... UNIX SHELL SIMULATOR(DEMO VERSION WITH PRELOADED COMMANDS)
$ cat dup.c # to open the file emp.lst /* Program: dup.c -- Uses dup to achieve both input and output redirection Closes standard streams first before using dup */
#include <stdio.h>
#include <unistd.h>
#include <sys/stat.h>
#include <fcntl.h>
#define MODE600 (S_IRUSR | S_IWUSR)
int main(int argc,char **argv) {
int fd1,int fd2;
fd1 = open(argv[1],O_RDONLY);
fd2 = open(argv[2], O_WRONLY | O_CREAT |O_TRUNC, MODE600);
close(STDIN_FILENO); /*This should return descriptor 0 */
dup(fd1);
close(STDOUT_FILENO); /*This should return descriptor 1 */
dup(fd2);
execvp(argv[3], &argv[3]); /* Execute any filter */
printf("Failed to exec filter");
}
$ cc shell.c $ a.out /etc/passwd passwd.cnt wc -1 cat passwd.cnt 37 /etc/passwd
$ exit #To exit the current simulation terminal and return to Scilab console
........# (hit [ENTER] for result)
BACK TO SCILAB CONSOLE...
Loading initial environment
-->diary(0)
|
