How to execute a shell script from C in Linux?

by

It depends on what you want to do with the script (or any other program you want to run).

If you just want to run the script system is the easiest thing to do, but it does some other stuff too, including running a shell and having it run the command (/bin/sh under most *nix).

If you want to either feed the shell script via its standard input or consume its standard output you can use popen (and pclose) to set up a pipe. This also uses the shell (/bin/sh under most *nix) to run the command.

Both of these are library functions that do a lot under the hood, but if they don’t meet your needs (or you just want to experiment and learn) you can also use system calls directly. This also allows you do avoid having the shell (/bin/sh) run your command for you.

The system calls of interest are fork, execve, and waitpid. You may want to use one of the library wrappers around execve (type man 3 exec for a list of them). You may also want to use one of the other wait functions (man 2 wait has them all). Additionally you may be interested in the system calls clone and vfork which are related to fork.

fork duplicates the current program, where the only main difference is that the new process gets 0 returned from the call to fork. The parent process gets the new process’s process id (or an error) returned.

execve replaces the current program with a new program (keeping the same process id).

waitpid is used by a parent process to wait on a particular child process to finish.

Having the fork and execve steps separate allows programs to do some setup for the new process before it is created (without messing up itself). These include changing standard input, output, and stderr to be different files than the parent process used, changing the user or group of the process, closing files that the child won’t need, changing the session, or changing the environmental variables.

You may also be interested in the pipe and dup2 system calls. pipe creates a pipe (with both an input and an output file descriptor). dup2 duplicates a file descriptor as a specific file descriptor (dup is similar but duplicates a file descriptor to the lowest available file descriptor).

More Related Contents:

  1. fd leak, custom Shell
  2. Implementation of multiple pipes in C
  3. Executing shell script with system() returns 256. What does that mean?
  4. Pipes, dup2 and exec()
  5. argv: Sanitizing wildcards
  6. what the output of this code and why?
  7. How to make child process die after parent exits?
  8. What is time_t ultimately a typedef to?
  9. What is the equivalent to Posix popen() in the Win32 API?
  10. How to recursively list directories in C on Linux?
  11. How does kernel get an executable binary file running under linux?
  12. Measure time in Linux – time vs clock vs getrusage vs clock_gettime vs gettimeofday vs timespec_get?
  13. Is malloc/free a syscall or a library routine provided by libc?
  14. Creating a new directory in C
  15. Building a kernel module from several source files which one of them has the same name as the module
  16. Turn a simple socket into an SSL socket
  17. Bind failed: Address already in use
  18. Why do I have to define LD_LIBRARY_PATH with an export every time I run my application?
  19. Is there a macro definition to check the Linux kernel version?
  20. Writing to a closed, local TCP socket not failing
  21. Write to .txt file?
  22. Do forked child processes use the same semaphore?
  23. What’s a good C decompiler? [closed]
  24. How to set the IP address from C in linux
  25. In C, what’s the size of stdout buffer?
  26. What can cause a “Resource temporarily unavailable” on sock send() command
  27. Returning struct containing array
  28. C: Different implementation of clock() in Windows and other OS?
  29. What is ‘:-!!’ in C?
  30. Where can I find system call source code?

Leave a Comment