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c executing shell problem

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# 1  
Old 11-27-2009
c executing shell problem
Hello
im geting error here:

Code:
#include <stdlib.h>
#include <stdio.h>
using namespace std;
int main (int argc, char *argv[])
{
char user[20];
string command;
 cin << user;
command = printf ("grep '%s' /etc/shadow", user);

system (command.c_str());
 }
 return 0;
}

it should search shadow file for a entered user, but it shows "sh not found"
# 2  
Old 11-27-2009
to start off:
Code:
printf ("grep '%s' /etc/shadow", user);

Is not a valid command in sh or bash.

What system does -
1. fork a new process
2. exec a shell in the child process and pass the arguments to to it
3. wait until the child process is done
4. get status from wait (see man 2 wait nad man system for exact details)

When you are at the command line:
show the output of
Code:
ls /bin/sh

What does your system manpage say about the default name of the shell it intends to use? -- it may refer you to exec...
# 3  
Old 11-27-2009
Code:
#include <stdlib.h>
#include <stdio.h>
using namespace std;
int main (int argc, char *argv[])
{
char user[20];
string command;
 cin << user;
command = printf ("grep '%s' /etc/shadow", user);

system (command.c_str());
 }
 return 0;
}

I'm surprised this even compiles. How did you get namespace::std or cin without iostream?

also, printf doesn't work that way. printf prints to stdout. If you want to print to a string, you use sprintf, like this:

Code:
char buf[512];
sprintf(buf, "grep '%s' /etc/shadow", user);



---------- Post updated at 12:49 PM ---------- Previous update was at 12:48 PM ----------

Lastly, why write a C command to run a shell command? wouldn't it be easier to run the shell command in the first place?
# 4  
Old 11-28-2009
Why not do it all from within C using the getpwent() et al APIs? Much safer.
# 5  
Old 12-03-2009
hi..
why dont you use exec family of functions to execute shell scripts from within the C program.
you can use execlp.
plz check the exec family of functions. its the most portable and simple way of executing shell commands. plz reply to extend this conversation. Smilie
regards
ttyl
# 6  
Old 12-05-2009
#include <stdlib.h>
#include <stdio.h>
using namespace std;
int main (int argc, char *argv[])
{
char user[20];
string command; ---> char command[25];
cin << user; ----> cin>>user;
command = printf ("grep '%s' /etc/shadow", user); --->

sprintf(command,"grep '%s' /etc/shadow", user)

system (command.c_str());

return 0;
}


Try this..
# 7  
Old 12-06-2009
Please use
Code:
code tags

Why to mix printf with cin, just use scanf instead of cin?
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