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);

}