Detailed explanation of system() function usage

system() function usage: 1. Directly call the system() function and pass in the system command string to be executed; 2. The return value of the system() function indicates the execution result of the system command. You can use this The return value is used to determine the execution result of the command, and then take corresponding processing measures; 3. The system() function can accept parameters in the command string; 4. The input and output of the command will be shared with the input and output of the program; 5. system( ) function will directly execute the incoming command string. Pay special attention to the security of the command.

# The system() function is a C language library function used to execute system commands in the operating system. Its function prototype is:

int system(const char *command);

Among them, the command parameter is a string representing the system command to be executed. The function return value represents the execution result of the system command. If the execution is successful, it returns 0, otherwise it returns a non-zero value.

The system() function is very powerful and can be used to execute various system commands, such as creating files, deleting files, running programs, etc. It can help us call the functions provided by the operating system in the program to achieve more complex operations.

The following is a detailed introduction to the usage of the system() function and some precautions.

Basic usage

The simplest usage is to directly call the system() function and pass in the system command string to be executed. For example, the following code will execute a simple command in the system:

#include <stdlib.h>
int main() {
    system("ls -l");
    return 0;
}

In the above code, system("ls -l") will execute the ls -l command in the Linux system and display the files in the current directory. File and folder details.

Command execution result

The return value of the system() function indicates the execution result of the system command. If 0 is returned, the command execution was successful; if a non-zero value is returned, the command execution failed.

You can use this return value to judge the execution result of the command, and then take corresponding processing measures. For example, the following code will output a prompt message when the command execution is successful:

#include <stdlib.h>
#include <stdio.h>
int main() {
    int result = system("ls -l");
    if (result == 0) {
        printf("Command executed successfully.\n");
    } else {
        printf("Command execution failed.\n");
    }
    return 0;
}

Command parameters

The system() function can accept parameters in the command string. Parameters can be separated by spaces or tabs. For example, the following code will execute a command with parameters:

#include <stdlib.h>
int main() {
    system("gcc -o hello hello.c");
    return 0;
}

The above code will execute the gcc -o hello hello.c command in the system and compile the hello.c file into the executable file hello.

Command input and output

When the system() function executes a system command, by default, the input and output of the command will be bound to the input and output of the current program. Set together. That is, the input and output of the command are shared with the input and output of the program.

If we want to separate the input and output of the command, we can use the redirection symbol. For example, the following code will redirect the output of the command to a file:

#include <stdlib.h>
int main() {
    system("ls -l > output.txt");
    return 0;
}

The above code will execute the ls -l command on the system and redirect the output to the output.txt file.

Command security

Because the system() function will directly execute the incoming command string, special attention should be paid to the security of the command.

If the command string is entered by the user, it should be strictly checked and filtered to prevent the user from entering malicious commands. For example, you can use string processing functions to filter out illegal characters or sensitive commands.

In addition, in order to increase the security of the program, other functions can be used to replace the system() function. For example, you can use the exec() series of functions to execute commands. These functions can directly specify the executable file to be executed and will not call the shell interpreter.

Summary:

The system() function is a very practical function that can help us execute system commands in the program. However, since it executes the command string passed in by the user, special attention must be paid to the security of the command when using it to avoid causing security holes in the system. In addition, pay attention to the input and output of commands and the processing of return values ​​to achieve more flexible and accurate operations.

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