What is System() Function in C?

Answer: ‘system()’ function is used to execute SHELL COMMANDS which we can’t use directly in C programs. Note here that program execution doesn’t complete until the COMMAND has completed. This function is defined in ‘stdlib.h’ header and is prototyped as below

    int system(char const *COMMAND);

Note that COMMAND is passed as a string. ‘system()’ function, then, passes this COMMAND to the host environment so that it can be executed as a command by the systems’ command processor. To ensure if command processor exists, call system() with NULL argument and check the return value if it’s non-zero. Let’s work with a simple C program to see how ‘system()’ works on Linux Machine.

/* system.c -- program calls system() to execute SHELL COMMANDS */
#include <stdio.h>
#include <stdlib.h>
#include <assert.h>
 
int main(void)
{
    int status;
 
    /* assert if command processor is available */
    assert((system(NULL)) != 0);
 
    /* let's attempt to execute SHELL commands */
    system("ls -l");
 
    /* do some more processing here */
 
    exit(0);
}

Try to execute above program and observe the output! Notice that ‘assert()’ function ensures if command processor is available.