system(3) — Linux man page
system() executes a command specified in command by calling /bin/sh -c command, and returns after the command has been completed. During execution of the command, SIGCHLD will be blocked, and SIGINT and SIGQUIT will be ignored.
Return Value
The value returned is -1 on error (e.g., fork(2) failed), and the return status of the command otherwise. This latter return status is in the format specified in wait(2). Thus, the exit code of the command will be WEXITSTATUS(status). In case /bin/sh could not be executed, the exit status will be that of a command that does exit(127).
If the value of command is NULL, system() returns nonzero if the shell is available, and zero if not.
system() does not affect the wait status of any other children.
Conforming to
Notes
If the _XOPEN_SOURCE feature test macro is defined (before including any header files), then the macros described in wait(2) (WEXITSTATUS(), etc.) are made available when including .
As mentioned, system() ignores SIGINT and SIGQUIT. This may make programs that call it from a loop uninterruptible, unless they take care themselves to check the exit status of the child. E.g.
Do not use system() from a program with set-user-ID or set-group-ID privileges, because strange values for some environment variables might be used to subvert system integrity. Use the exec(3) family of functions instead, but not execlp(3) or execvp(3). system() will not, in fact, work properly from programs with set-user-ID or set-group-ID privileges on systems on which /bin/sh is bash version 2, since bash 2 drops privileges on startup. (Debian uses a modified bash which does not do this when invoked as sh.)
In versions of glibc before 2.1.3, the check for the availability of /bin/sh was not actually performed if command was NULL; instead it was always assumed to be available, and system() always returned 1 in this case. Since glibc 2.1.3, this check is performed because, even though POSIX.1-2001 requires a conforming implementation to provide a shell, that shell may not be available or executable if the calling program has previously called chroot(2) (which is not specified by POSIX.1-2001).
It is possible for the shell command to return 127, so that code is not a sure indication that the execve(2) call failed.
System() Function in C Language
The Linux command console is undoubtedly something like the living room of all of us who are fans of this operating system. The countless commands that Linux offers are part of our daily work environment and many of them we know and use by heart. The possibility of executing these commands in Linux from our C code and interacting directly with the operating system from there opens up a number of very useful resources for the programmer.
In this Linux Hint article, we will explain everything that you need to know to execute the commands from C code using the system() function. We will explain the theoretical framework of this function, its input and output arguments, and the type of data it accepts in each case. We will then apply what we learned in a practical example that includes the code snippets where we execute the various Linux commands from our C code.
Syntax of the System() Function in C Language
Description of the System() Function in C Language
The system() function executes a command in the Linux system shell or another OS.
If the command is executed correctly, system() returns “0”.
This function has a pointer to the string str as its only input argument, which contains the command to be executed in the system verbatim and without syntax errors.
The system() function executes the commands in the Linux system, but does not retrieve any information or return any results of the executed command.
System() is part of the “stdlib” standard library. To use it, we must include it in our code file as follows:
Once the “stdlib.h” library is included, we can use the system() function.
Next, we will see some examples of using the system() function to execute the various commands in the Linux interpreter.
Example 1: How to Execute a Command in the Linux Interpreter Using the System() Function in C
In this example, we open a file with the fopen() function and use the system() function to send a beep to the system in case of an opening error.
The fopen() function returns 0 if an error occurs when opening the file. We put this value as a condition in an if-condition and execute the “beep” command in the interpreter with system( ) to inform the user about its error.
We see the code for this purpose in the following illustration. In the path that specifies the file, we put the name of a non-existent file to generate an error:
f_Ptr = fopen ( «Documents/ not exist» , «r» ) ;
Example 2: How to Recognize Whether the Command Executed with the System() Function Is Interpreted Correctly
In this example, we explain how to determine whether the command is executed correctly in the Linux console. An error in the execution of the command itself does not refer to an error in the execution of the system() function. Therefore, the system does not log this exception in the error code variable, “errno”.
As mentioned in the description, the system() function executes the commands on the system, but does not return the results.
The output argument of this function is an integer which returns “0” if the command is successfully executed on the system. Otherwise, it returns another value.
Next, we see a code fragment where we use the return of the system() function to determine if the command is executed correctly.
In this code, we send the “beep” command. But for the practice of this example, we can send the various correct and incorrect commands into the input argument of the system() function to see the different results.
We use the return of the system() function as a condition in an if-else condition. If the command is executed correctly, a message is displayed on the screen with the following text:
“The command was executed successfully.”
Otherwise, the following message is displayed:
“The command was not recognized or could not be executed.”
printf ( “ The command was executed successfully \n » ) ;
Using system() function in c
I want to use the system function to get the number of accounts on windows and on linux. I have no idea where to look. Please just point me in the right direction.
Welcome to Stack Overflow. Please read the FAQ before too long. What have you tried? What constitutes an account? Where do you look for information about accounts on Linux? Where do you look for information about accounts on Windows? What command would you run from the shell, because that’s the command you’ll run via system() ? If you don’t know the way to do it at the shell (CMD window prompt) you’re on a hiding to nothing. Research that first; when you can get the answer outside your C code, getting it with system() inside your C code is child’s play.
4 Answers 4
The system() function runs a program. If you know a command line that does what you need, you can use system() to run that command line.
I’m not sure what command-line program would give the number of accounts on Windows. You could get an approximation by looking at the number of home directories. On Windows the home directories are in \Users and on Linux home directories are in `/home’.
The system() function doesn’t capture the output of the program. You would then likely need to run a command line that redirects the program output to a file, then open this file and parse the output.
You would probably have an easier time solving this problem using a language like Python. Python programs are very portable and there are some wrappers for system stuff.
«Python programs are very portable». How many Sega Megadrives do you know that’ll run a Python implementation?
That is an irrelevant indication of the portability of Windows or Linux, not the portability of Python programs.