system() Function

The system() function is declared in the header file <stdlib.h>.

The system() function enables a program to execute an operating system command by invoking the command processor. It provides a simple interface to run shell commands directly from your C code, allowing integration with the host system’s command environment.

Syntax of system()

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int system(const char* command);

Parameters

ParameterDescription
commandA C-string containing the command to be executed. Alternatively, a null pointer can be passed to check if a command processor is available.

Note that if command is a null pointer, system() will not execute any command but will simply check for the presence of a command processor. The behavior and return value when executing a command may vary depending on the system and library implementation.

Return Value

If command is a null pointer, the function returns a nonzero value if a command processor is available and zero if not. If command is not a null pointer, the return value is typically the status code returned by the executed command, though this is system-dependent.

Examples for system()

Example 1: Executing a Simple Shell Command

This example demonstrates how to use system() to execute a simple shell command that prints a message to the console.

Program

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#include <stdio.h>
#include <stdlib.h>

int main() {
    /* Execute a simple command to print a message */
    int status = system("echo Hello, World!");
    
    /* Print the status code returned by the command */
    printf("Command exited with status: %d\n", status);
    return 0;
}

Explanation:

  1. The program calls system() with the command "echo Hello, World!" to print a message.
  2. The status code returned by the command is stored in the variable status.
  3. The status code is printed to the console.

Program Output:

Hello, World!
Command exited with status: 0

Example 2: Checking for a Command Processor

This example demonstrates how to use system() with a null pointer to check whether a command processor is available on the system.

Program

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#include <stdio.h>
#include <stdlib.h>

int main() {
    /* Check if a command processor is available */
    int available = system(NULL);
    
    if (available) {
        printf("A command processor is available.\n");
    } else {
        printf("No command processor available.\n");
    }
    return 0;
}

Explanation:

  1. The program calls system(NULL) to check for the availability of a command processor.
  2. The return value is nonzero if a command processor is available and zero otherwise.
  3. A corresponding message is printed based on the result.

Program Output:

A command processor is available.

Example 3: Executing a Directory Listing Command

This example uses system() to execute a command that lists the contents of the current directory. Note that the specific command may vary between operating systems.

Program

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#include <stdio.h>
#include <stdlib.h>

int main() {
    /* Execute a directory listing command */
    #if defined(_WIN32) || defined(_WIN64)
        int status = system("dir");
    #else
        int status = system("ls -l");
    #endif
    
    printf("Directory listing command exited with status: %d\n", status);
    return 0;
}

Explanation:

  1. The program conditionally compiles the appropriate command for the operating system: "dir" for Windows and "ls -l" for Unix-like systems.
  2. The system() function is used to execute the directory listing command.
  3. The exit status of the command is captured and printed.

Program Output:

total 20
-rwxr-xr-x 1 tutorialkart tutorialkart 16008 Feb 23 13:39 a.out
-rw-r--r-- 1 tutorialkart tutorialkart   331 Feb 23 13:39 main.c
Directory listing command exited with status: 0