Execute shell/bash command using C/C++
In this article I’ll explain how to execute a shell command using a c/c++ program.
There’s an advanced example included, reading line by line from a file and executing a command for each line.
There are a few options that you can use: execl, execlp, execle, execv, execvp, but in this example I’ll use system.
Let’s begin with a simple example:
#include <cstdlib>
#include <cstdio>
using namespace std;
int main()
{
// declaration of record
char record[1000];
// prints the shell command into record
sprintf(record,"/bin/ls");
// this executes what record contains
system(record);
return 0;
}
A short description of include headers:
cstdlib - includes functions involving memory allocation, process control, conversions, and so on
cstdio - contains macro definitions, constants, and declarations of functions and types
using namespace std – is a collection of classes and functions, which are written in the core language and part of the C++ ISO Standard itself
How to compile this under linux, first of all you need GCC installed, compile it like this if you do have it installed:
g++ -o filename filename.cpp
Now let’s see a more complex example:
#include <cstdlib>
#include <cstdio>
// required in order to open a file
#include <fstream>
using namespace std;
int main()
{
// declaration of line as a string
string line;
// opens iplist for reading
ifstream myfile ("/home/iplist");
char record[1000];
// if the file was successfully opened "continue"
if (myfile.is_open())
{
// reading from file until reaching end of file EOF
while (! myfile.eof() )
{
// get line by line from file and store it in the variable line
getline (myfile,line);
// stores the to be executed command into "record", %s is replaced by the content of "line"
sprintf(record,"/sbin/iptables -A INPUT -s %s -j ACCEPT", line.c_str());
// executes the actual command
system(record);
}
// after we are done with the file we need to close it
myfile.close();
}
// in case the file can't be opened, the program prints this message on a new line
else printf("Unable to open file\n");
return 0;
}
What is this program doing?
It starts by opening the file “/home/iplist” for reading.
Next, if the file is opened it will start executing the while loop, else it will print “Unable to open file” on a new line.
The while loop will execute the shell command for every line in the file.
Let’s say that you have the file /home/iplist containing this lines:
192.168.0.2 10.10.2.4
Your program will execute the following commands:
iptables -A INPUT -s 192.168.0.2 -j ACCEPT iptables -A INPUT -s 10.10.2.4 -j ACCEPT
