I want to create a program in C that displays the router password using telnet protocol. The instruction to do that from cmd is:
open CMD
Type telnet <router ip>
Type the router dashboard User
Type the router dashboard password
Type wireless default
I try with
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
int main(int argc, char *argv[])
{
system("telnet 192.168.1.1");
system("Menara");
system("Menara");
system("wireless default");
system("PAUSE");
return 0;
}
but the program stops at the second argument so I assume that system() cannot communicate with telnet. Can someone give me the correct code?
You need to open a pipe to the telnet command and send commands to it. Look at the popen() function in C and look at this StackOverflow question.
Here is a code example (taken from the StackOverflow question that I just pointed before):
#include <stdio.h>
int main()
{
FILE *fp = popen("telnet 192.168.1.1","w");
fprintf(fp, "Menara\n");
fprintf(fp, "Menara\n");
fprintf(fp, "PAUSE\n");
if (pclose(fp) != 0) {
/* Error reported by pclose() */
fprintf (stderr, "Could not run more or other error.\n");
}
return 0;
}
Related
I am attempting to write a simple program that calls git checkout -- . on a Github repo that would be a command line argument. I would like to call it like > clearRepo repoName. I keep all my repos in the same Github directory.
The code is as follows:
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <string.h>
#include <errno.h>
void print_error()
{
fprintf(stderr, "Error executing: %s\n", strerror(errno));
exit(EXIT_FAILURE);
}
void print_usage(char* this)
{
printf("SYNTAX ERROR:\n%s [directoryName]\n", this);
exit(EXIT_FAILURE);
}
int main(int argc, char **argv)
{
if(argc != 2)
{
print_usage(argv[0]);
}
pid_t pid = fork();
if (pid == 0)
{
static char* params[] = {"git", "checkout", "--", ".", NULL};
char s[50], s2[50];
strcpy(s, "/home/myname/Documents/Github/");
strcpy(s2, argv[1]);
strcat(s, s2);
printf("s: %s\n", s);
int err = execv(s, params);
if(err == -1)
{
print_error();
}
exit(127);
}
else
{
waitpid(pid, 0, 0);
}
return 0;
}
It compiles fine, but print_error() will spit out Error executing: Permission denied every time I run it. I am not too familiar with writing programs for Linux, so it is probably a simple mistake. Information on what I'm doing wrong is appreciated. Thanks.
The first argument you're passing to execv is a directory, but execv expects a program. The error "Permission denied" is slightly misleading, because there is no such thing as "permission to execute directories".
To change the current directory, call chdir. Then, call whichever one of the exec* functions you like to invoke git.
chmod u+x filename for changing file permission.
If you want to checkout of a branch, but save the changes, use git stash. You can use git stash pop or git stash apply when you come back to the branch.
https://git-scm.com/docs/git-stash
Git commands and programs are quite tricky.
Follow these steps and you might debug your problem.
Enter the git commands written in the program into a terminal and check if the logic actually works. (Suggested this as you said you were new to Linux)
If it works, change the permission of your file by typing "chmod +x filename.extention".
My problem is to deal with sparse file reads and understand where the extents of the file are to perform some logic around it.
Since, there is no direct API call to figure these stuff out, I decided to use ioctl api to do this. I got the idea from how cp command deals with problems of copying over sparse files by going through their code and ended up seeing this.
https://github.com/coreutils/coreutils/blob/df88fce71651afb2c3456967a142db0ae4bf9906/src/extent-scan.c#L112
So, I tried to do the same thing in my sample program running in user space and it errors out with "Invalid argument". I am not sure what I am missing or if this is even possible from userspace. I am running on ubuntu 14.04 on an ext4 file system. Could this be a problem with device driver supporting these request modes underneath?
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <sys/fcntl.h>
#include <errno.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <unistd.h>
#include <sys/ioctl.h>
#include <linux/fs.h>
#include "fiemap.h" //This is from https://github.com/coreutils/coreutils/blob/df88fce71651afb2c3456967a142db0ae4bf9906/src/fiemap.h
int main(int argc, char* argv[]) {
int input_fd;
if(argc != 2){
printf ("Usage: ioctl file1");
return 1;
}
/* Create input file descriptor */
input_fd = open (argv [1], O_RDWR);
if (input_fd < 0) {
perror ("open");
return 2;
}
union { struct fiemap f; char c[4096]; } fiemap_buf;
struct fiemap *fiemap = &fiemap_buf.f;
int s = ioctl(input_fd, FS_IOC_FIEMAP, fiemap);
if (s == 0) {
printf("ioctl success\n");
} else {
printf("ioctl failure\n");
char * errmsg = strerror(errno);
printf("error: %d %s\n", errno, errmsg);
}
/* Close file descriptors */
close (input_fd);
return s;
}
As you're not properly setting the fiemap_buf.f parameters before invoking ioctl(), it is likely that the EINVAL is coming from the fiemap invalid contents than from the FS_IOC_FIEMAP request identifier support itself.
For instance, the ioctl_fiemap() (from kernel) will evaluate the fiemap.fm_extent_count in order to determine if it is greater than FIEMAP_MAX_EXTENTS and return -EINVAL in that case. Since no memory reset nor parameterization is being performed on fiemap, this is very likely the root cause of the problem.
Note that from the coreutils code you referenced, it performs the correct parameterization of fiemap before calling ioctl():
fiemap->fm_start = scan->scan_start;
fiemap->fm_flags = scan->fm_flags;
fiemap->fm_extent_count = count;
fiemap->fm_length = FIEMAP_MAX_OFFSET - scan->scan_start;
Note fiemap is not recommended as you have to be sure to pass FIEMAP_FLAG_SYNC which has side effects. The lseek(), SEEK_DATA and SEEK_HOLE interface is the recommended one, though note that will, depending on file system, represent unwritten extents (allocated zeros) as holes.
I have a question, here is my original code in the testchdir.c file:
#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
int main(int argc,char **argv)
{
if (argc < 2)
{
printf("Usage: %s <pathname\n",argv[0]);
exit(1);
}
if (chdir(argv[1]) == 0)
{
printf("success in chdir\n");
return 0;
}
else
{
printf("error happened");
exit(1);
}
}
In my Linux system, my original path is /home/Tom3543, then when I compile my codes above using gcc -o testchdir testchdir.c, it looks good. Later on, I want to change my path and execute the program, so I type
./testchdir /home/tom3543/C++
"success in chdir" appeared in my terminal, but my path is still /home/Tom3543 in my terminal. Can someone help me explain why? I am confused about that!
It's because the shell starts a new process for your program, and you only change the current directory in that new process. The shells process will be unaffected.
Unfortunately (for you) there's no real good (or legal) way to change the working directory of the parent process (the process of the shell).
I have a binary called TEST which spawns a bash shell, I was hoping to write a C program that runs TEST and then passes commands to the bash shell that it spawns - I have tried the following - can someone indicate if this is possible. I can run the file using, but don't know how to then pass commands to shell it spawns:
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
int main()
{
system("/var/testfolder/TEST"); #run the test file
return 0;
}
The UNIX styled popen() function is what you want to use.
See the man page for specifics.
It runs your command in a subprocess and gives you a pipe to interact with it. It returns a FILE handle like fopen() does, but you close it with pclose() rather than fclose(). Otherwise you can interact with the pipe the same way as for a file stream. Very easy to use and useful.
Here's a link to a use case example
Also check out this example illustrating a way to do what you are trying to do:
#include <stdio.h>
int main(void) {
FILE *in;
extern FILE *popen();
char buf[512];
if (!(in = popen("ls -sail", "r")))
exit(1);
while (fgets(buf, sizeof(buf), in) != NULL)
printf("%s", buf);
pclose(in);
}
How do I programmatically open a file in its default program in Linux (im using Ubuntu 10.10).
For example, opening *.mp3 will open the file in Movie Player (or something else).
You need to run gnome-open, kde-open, or exo-open, depending on which desktop you are using.
I believe there is a project called xdg-utils that attempts to provide a unified interface to the local desktop.
So, something like:
snprintf(s, sizeof s, "%s %s", "xdg-open", the_file);
system(s);
Beware of code injection. It's safer to bypass scripting layers with user input, so consider something like:
pid = fork();
if (pid == 0) {
execl("/usr/bin/xdg-open", "xdg-open", the_file, (char *)0);
exit(1);
}
// parent will usually wait for child here
Ubuntu 10.10 is based on GNOME. So, it would be good idea to use
g_app_info_launch_default_for_uri().
Something like this should work.
#include <stdio.h>
#include <gio/gio.h>
int main(int argc, char *argv[])
{
gboolean ret;
GError *error = NULL;
g_type_init();
ret = g_app_info_launch_default_for_uri("file:///etc/passwd",
NULL,
&error);
if (ret)
g_message("worked");
else
g_message("nop: %s", error->message);
return 0;
}
BTW, xdg-open, a shell script, tries to determin your desktop environment and call a known helper like gvfs-open for GNOME, kde-open for KDE, or something else. gvfs-open ends up calling g_app_info_launch_default_for_uri().
A simple solution with less coding:
I've tested this program on my Ubuntu and it is working fine, and if I am not wrong you are looking for something like this
#include <stdio.h>
#include <stdlib.h>
int main()
{
system("firefox file:///dox/song.mp3");
return 0;
}