Summarize the usage of system() function in Linux system

Summary of the system() function under Linux

In the Linux system, the system() function is a very commonly used function, which can be used to execute command line commands. This article will introduce the system() function in detail and provide some specific code examples.

1. Basic usage of the system() function

The declaration of the system() function is as follows:

int system(const char *command);

Among them, the command parameter is a string indicating the command to be executed. .

The function of the system() function is to execute commands in a child process and wait for the completion of command execution. The execution of the command is achieved by calling the shell.

When command is NULL, the system() function just checks the availability of the current shell, which is equivalent to system(":")

The return value of the function is the result of the command execution. If the command is executed successfully, the return value is the exit status of the command. Under normal circumstances, the command execution returns 0 successfully, otherwise it returns a non-zero value.

2. Basic Example

The following is a simple example that demonstrates how to use the system() function to execute the ls command:

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

int main()
{
    int result = system("ls");
    if(result == 0)
    {
        printf("Command executed successfully
");
    }
    else
    {
        printf("Command execution failed
");
    }
    return 0;
}

In the above example, by calling system( "ls") executes the ls command, and then determines whether the command is executed successfully based on the return value.

3. System call

The system() function is actually implemented by calling system calls such as fork(), execve() and waitpid().

First, the system() function calls fork() to create a new child process. The child process is responsible for executing the commands to be executed.

Then, the child process calls the execve() function to reload an executable program to replace itself. Here, call /bin/sh to execute the command.

The parent process calls the waitpid() function and waits for the child process to complete execution.

4. Security considerations

When using the system() function, you need to pay attention to some security issues. Because the system() function executes commands entered by the user, there are security risks such as command injection and path traversal.

In order to improve security, we should follow the following principles:

1. Never pass user input directly to the system() function. User input should be validated and filtered.
2. Use absolute paths to execute commands to avoid being affected by the PATH environment variable.
3. For parameters that may contain special characters, quotation marks, escape characters, etc. should be used for processing.

5. Summary

This article introduces the system() function under Linux and provides some code examples. The system() function can conveniently execute command line commands, but you need to pay attention to security issues when using it. Proper use of the system() function can improve the flexibility and functional scalability of the program.

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