running external commands

1. To run external commands while editing a file in vim, use the '!' in the normal mode. For example
   

   :!ls -al
   

   will list the files
   

   :!date
   

   will display the current date.
   
   
2. To read the output of external commands into the current file, do
   

   :r !date
   

   All the commands are run in normal mode. Press ESC key to enter the normal mode in vim.
   
   Further reading:- :help :!
   
   
3. To run external commands in octave, use the system command. Sample octave session looks as
   

   $octave -q
   octave:1> system("date")
   Thu Jun  4 23:49:23 EDT 2009
   ans = 0
   octave:2> [ret_code output] = system("date");
   octave:3> ret_code
   ret_code = 0
   octave:4> output
   output = Thu Jun  4 23:49:40 EDT 2009
   
   octave:5> exit

   Further reading :- "doc system" shows the relevant help pages in octave.
   
   
4. To run external commands in Fortran 90 programs, use the system command. Sample code looks as below
   

   $cat system.f90
   program callsystem
          implicit none
          !to examine the behaviour of the system command
          character (len=100)::cmd
          cmd="echo Wake up Neo"
          !if u are using ifc compiler use -Vaxlib during compilation
          call system(cmd//achar(0))
          call system(cmd)
          call system("date")
          ! The next line also works.
          ! call system("ls")
   end program callsystem
   
   $gfortran system.f90
   
   $./a.out
   Wake up Neo
   Wake up Neo
   Thu Jun  4 23:55:07 EDT 2009

5. To run the external commands in C, use the system command available in stdlib.h. Sample code will be
   

   $cat system.c
   #include stdio.h
   #include stdlib.h
   
   int main() {
        /* Fixme :- <, > in the header files are not showing up on blogspot */
        int ret_code;
        ret_code = system("date");
   
        printf("%d\n", ret_code);
        return 0;
   }
   
   $gcc -Wall system.c
   
   $./a.out
   Fri Jun  5 00:04:14 EDT 2009
   0

   
   Further reading :- man system
   
   All the above are tested in Debian Lenny using vim 7.1, octave 3.0.1, gfortran 4.3.1, gcc 4.3.1