It's not clear which of two things you are asking

• How to run an arbitrary external command line, which may or may not be the binary executable produced by compiling a C program.
• How to call C code (say, as a subroutine call) directly from perl.

1. Run the command with back-ticks, assigning its STDOUT to a variable: as in, my $result = `commandline`;
2. Use the system() function: as in, my $rc = system("commandline > result.log");
3. Open the command as a pipe (if, say, you expect lots of output):

   # note vertical bar (pipe) at end of command
   open PH, "commandline|" or die "commandline: $!";
   while (<PH>) {
      # ... do something with each line of output
   }
   close PH or die "commandline: $!";
   [download]

The answer to the second question is too involved to cover adequately here, but has been covered in depth elsewhere, among which are this and this.

Update: Another option, as posited by Sniper, is of course to use Inline.pm, but once again, that's a whole 'nother ball of wax.

dmm