if(numpipes==0)
{	// single command
}
else
{	int fdsl[2];	// file descriptors currently dealing the pipe to the left of the current process
	int fdsr[2];	// file decsriptors currently dealing the pipe to the left of the current process
	char** argv=new char*[cmd2.size()];
	int i=0,j;

	if(pipe(fdsr)<0)
	{	//error
	}
	for(j=0;cmd2[i+j]!="|"&&i+j<cmd2.size();++j)
	{	argv[j]=new char[cmd2[i+j].length()+1];
		strcpy(argv[j],cmd2[i+j].c_str());
	}
	argv[j]=NULL;
	i=j+1;
	pid=fork();
	if(pid<0)
	{	//error
	}
	else if(pid==0)
	{	dup2(fdsr[1],1);
		close(fdsr[0]);
		close(fdsr[1]);
		execvp(argv[0],argv);
		// error
		_exit(errno==ENOENT?127:126);
	}
	for(j=0;argv[j];++j)
	{	delete[] argv[j];
	}

	for(int pipesdone=1;pipesdone<numpipes&&i<cmd2.size();++pipesdone)
	{	fdsl[0]=fdsr[0];
		fdsl[1]=fdsr[1];
		if(pipe(fdsr)<0)
		{	//error
		}
		for(j=0;cmd2[i+j]!="|"&&i+j<cmd2.size();++j)
		{	argv[j]=new char[cmd2[i+j].length()+1];
			strcpy(argv[j],cmd2[i+j].c_str());
		}
		argv[j]=NULL;
		i=j+1;
		pid=fork();
		if(pid<0)
		{	//error
		}
		else if(pid==0)
		{	dup2(fdsl[0],0);
			dup2(fdsr[1],1);
			close(fdsl[0]);
			close(fdsl[1]);
			close(fdsr[0]);
			close(fdsr[1]);
			execvp(argv[0],argv);
			// error
			_exit(errno==ENOENT?127:126);
		}
		for(j=0;argv[j];++j)
		{	delete[] argv[j];
		}
		close(fdsl[0]);
		close(fdsl[1]);
	}

	fdsl[0]=fdsr[0];
	fdsl[1]=fdsr[1];
	for(j=0;cmd2[i+j]!="|"&&i+j<cmd2.size();++j)
	{	argv[j]=new char[cmd2[i+j].length()+1];
		strcpy(argv[j],cmd2[i+j].c_str());
	}
	argv[j]=NULL;
	i=j+1;
	pid=fork();
	if(pid<0)
	{	//error
	}
	else if(pid==0)
	{	dup2(fdsl[0],0);
		close(fdsl[0]);
		close(fdsl[1]);
		execvp(argv[0],argv);
		// error
		_exit(errno==ENOENT?127:126);
	}
	for(j=0;argv[j];++j)
	{	delete[] argv[j];
	}
	close(fdsl[0]);
	close(fdsl[1]);

	delete[] argv;
}