MIT 6.828 HW2 shell
Notes of MIT 6.828 HW2
In this HW, we implement several features in a small shell.
Executing simple commands
Fill the ‘’ case in runcmd.
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| case ' ':
ecmd = (struct execcmd*)cmd;
if(ecmd->argv[0] == 0)
_exit(0);
if ((execv(ecmd->argv[0], ecmd->argv) == -1))
fprintf(stderr, "execv failed\n");
break;
|
I/O redirection
Use the trick that open will choose the smallest free file descriptor.
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| case '>':
case '<':
rcmd = (struct redircmd*)cmd;
close(rcmd->fd);
if (open(rcmd->file, rcmd->flags, S_IRWXU) == -1) {
fprintf(stderr, "open failed\n");
break;
}
runcmd(rcmd->cmd);
break;
|
Implement Pipes
Use pipe and dup. Mind to close pipefds correctly and wait for child processes.
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| case '|':
pcmd = (struct pipecmd*)cmd;
int pipefds[2];
if ((pipe(pipefds)) == -1) {
fprintf(stderr, "create pipe failed\n");
}
int pid1, pid2;
if ((pid1 = fork1()) == 0) {
close(STDOUT_FILENO);
dup(pipefds[1]);
close(pipefds[0]);
close(pipefds[1]);
runcmd(pcmd->left);
}
else {
if ((pid2 = fork1()) == 0) {
close(STDIN_FILENO);
dup(pipefds[0]);
close(pipefds[0]);
close(pipefds[1]);
runcmd(pcmd->right);
}
else {
close(pipefds[0]);
close(pipefds[1]);
wait(&r);
wait(&r);
}
}
break;
|