Programming

fdin=fdpipe[0];
fdout=fdpipe[1];

$ uname -a
SunOS foobar 5.7 Generic_106541-08 sun4c sparc SUNW,Sun_4_50
$ /usr/local/bin/gcc ab.c -o ab
$ echo "fred" | ./ab
fdout=6,fdin=5
pid=274,tmpin=3,tmpout=4
fdout=6,fdin=5
pid=275,tmpin=3,tmpout=4
0+1 records in
0+1 records out
0+1 records in
0+1 records out
fdout=6,fdin=5
pid=276,tmpin=3,tmpout=4
0+1 records in
0+1 records out
pid=277,tmpin=3,tmpout=4
fred
0+1 records in
0+1 records out

#include <sys/types.h>
#include <sys/stat.h>
#include <sys/wait.h>
#include <stdio.h>
#include <unistd.h>
#include <errno.h>
#include <stdlib.h>
#include <fcntl.h>

struct cmd
{
  char **_arguments;
};

char *args[]={
	"dd",NULL,
	"dd",NULL,
	"dd",NULL,
	"dd",NULL
};

struct cmd cmdList[]={
	{args+0},
	{args+2},
	{args+4},
	{args+6}
};

struct cmd *_simpleCommands[]={
	cmdList+0,
	cmdList+1,
	cmdList+2,
	cmdList+3
};

char *_inputFile;
char *_outFile;

int main(int argc,char **argv)
{
int _background=0;
int _numberOfSimpleCommands=(sizeof(cmdList)
									/sizeof(cmdList[0]));
	int tmpin=dup(0);
	int tmpout=dup(1);
	int ret=-1;
	int fdout=-1;
	int fdin=-1;
	int i;
	int rc=0;

	if(_inputFile)
	{
	   fdin = open(_inputFile, O_RDONLY | O_CREAT, S_IREAD | S_IWRITE);
	}
	else
	{
	   fdin=dup(tmpin);
	}

	for (i = 0; i < _numberOfSimpleCommands; i++)
	{
	   rc=dup2(fdin, 0); if (rc==-1) perror("dup2(fdin)");
	   close(fdin); fdin=-1;

	   if(i == _numberOfSimpleCommands-1) 
	   {
	      if(_outFile)
	      {
	         fdout=open(_outFile, O_WRONLY | O_CREAT, S_IREAD | S_IWRITE);
	      }
	      else
	      {  
	         fdout=dup(tmpout);
	      }
	   }
	   else
	   {
	      int fdpipe[2];
	      pipe(fdpipe);
          fdin=fdpipe[0];
          fdout=fdpipe[1];

			fprintf(stderr,"fdout=%d,fdin=%d\n",fdout,fdin);
	    }

	    rc=dup2(fdout,1); if (rc==-1) perror("dup2(fdout)");

	    close(fdout); fdout=-1;

	    ret = fork();
	    if(ret==0)
	    {
			fprintf(stderr,"pid=%d,tmpin=%d,tmpout=%d\n",
					getpid(),tmpin,tmpout);			
			rc=close(tmpin); if (rc) perror("close(tmpin)");
			rc=close(tmpout); if (rc) perror("close(tmpout)");

			execvp( (*_simpleCommands)[i]._arguments[0],
					(*_simpleCommands)[i]._arguments);

	       	perror("execvp");
	       	exit(1);
	     }
	}

	rc=dup2(tmpin, 0); if (rc==-1) perror("dup2(tmpin,0)");
	rc=dup2(tmpout, 1); if (rc==-1) perror("dup2(tmpin,0)");
	close(tmpin);
	close(tmpout);
	
	if(!_background)
	{
		waitpid(ret, 0, 0);
	}

    return 0;
}