Тестовые примеры / ch8 / exec_cmd

	/* exec_cmd.C: 		Functions to execute one shell command input line */

	#include <iostream.h>

	#include <stdio.h>

	#include <stdlib.h>

	#include <unistd.h>

	#include <fcntl.h>

	#include <sys/wait.h>

	#include "shell.h"



	/* change the standard I/O port of a process */

	void chg_io( char* fileName, mode_t mode, int fdesc )

	{

 		int 	fd= open(fileName,mode,0777);

		 if (fd==-1) 

 			perror("open");

		 else 

		{

 			if (dup2(fd,fdesc)==-1) perror("dup2");

 			close(fd);

 		}

	}

 

	/* execute one or more command pipe */

	void exec_pipes( CMD_INFO *pCmd )

	{

 		CMD_INFO 		*ptr;

 		int 		fifo[2][2];

 		int 		bg=0, first=1, cur_pipe = 0;

 		pid_t 		pid;

 		while (ptr=pCmd) 

		{

 			pCmd = ptr->Pipe;

 			if (pipe(fifo[cur_pipe])==-1)

			{

 				perror("pipe"); return;

 			}

			switch(fork())

			{

 				case -1: 			perror("fork"); 

							return;

				case 0: 			if (!first)

							{	 						// not the first cmd

 								dup2(fifo[1-cur_pipe][0],0);

 								close(fifo[1-cur_pipe][0]);

 							}

 							else if (ptr->infile)

 								chg_io(ptr->infile,O_RDONLY,0);

						 	if (pCmd) 								// not the last cmd

 								dup2(fifo[cur_pipe][1],1);

 							else if (ptr->outfile)

 								chg_io(ptr->outfile,

											O_WRONLY|O_CREAT|O_TRUNC,1);

 							close(fifo[cur_pipe][0]);

 							close(fifo[cur_pipe][1]);

 							execvp(ptr->argv[0],ptr->argv);

						 	cerr << "Execute `" << ptr->argv[0] << "` fails\n";

 							exit(4);

			 }

			 if (!first) close(fifo[1-cur_pipe][0]);

 			close(fifo[cur_pipe][1]);

			cur_pipe = 1 - cur_pipe;

 			bg = ptr->backgrnd;

 			delete ptr;

			first = 0;

 		}

 		close(fifo[1-cur_pipe][0]);

 		while (!bg && (pid=waitpid(-1,0,0))!=-1) ;

	}



	/* execute one shell command line */

	void exec_cmd( CMD_INFO *pCmd )

	{

 		pid_t 		prim_pid, pid;

 		CMD_INFO 		*ptr = pCmd;



		// create a sub-shell to process one command line

 		switch( prim_pid = fork()) 

		{

 			case -1: 			perror("fork"); return;

 			case 0: 			break;

 			default: 			if (waitpid(prim_pid,0,0)!=prim_pid) 							perror("waitpid");

						return;

 		} 

		while (ptr=pCmd) 									// execute each command stage

		{

 			pCmd = ptr->Next;

 			if (ptr->Pipe) 

 				exec_pipes(ptr);	 						// execute one stage which has command pipes

 			else 

			{

 				// sub-process to execute one command stage

 				switch (pid=fork())

				{

					 case -1: 			perror("fork"); return;

 					case 0: 			break;

 					default: 			if (!ptr->backgrnd && waitpid(pid,0,0)!=pid)

 									perror("waitpid");

 								delete ptr;

 								continue;

 				}

				 if (ptr->infile) 

 					chg_io(ptr->infile,O_RDONLY,0);

 				if (ptr->outfile) 

					chg_io(ptr->outfile,O_WRONLY|O_CREAT|O_TRUNC,1);

				 if (ptr->argv) 

				{

					 execvp(ptr->argv[0], ptr->argv);

					 cerr << "Execute `" << ptr->argv[0] << "` fails\n";

 					exit(999);

 				} else 

				{

					 exec_cmd(ptr->pSubcmd);

					 exit(0);

 				}

 			} 

 		}

 		exit(0);

	}