tinybc.c

创建一个具有SHELL功能的小程序. 利用管道技术及FORK创建子进程

#include <stdio.h>
#define oops(m,x) {perror(m);exit(x);}
main()
{
int pid,todc[2],fromdc[2];
if(pipe(todc)==-1 || pipe(fromdc)==-1)
oops("pipe failed",1);
if((pid=fork())==-1)
oops("fork failed",2);
if(pid==0)
be_dc(todc,fromdc);
else{
be_bc(todc,fromdc);
wait(NULL);
}
}
be_dc(int in[2],int out[2])
{
if(dup2(in[0],0)==-1)
oops("dc: cannot rediret stdin",3);
close(in[0]);
close(in[1]);
if(dup2(out[1],1)==-1)
oops("dc: cannot rediret stdout",4);
close(out[1]);
close(out[0]);
execlp("dc","dc","-",NULL);
oops("cannot run dc",5);
}
be_bc(int todc[2],int fromdc[2])
{
int num1,num2;
char operation[BUFSIZ],message[BUFSIZ],*fgets();
FILE *fpout,*fpin,*fdopen();
close(todc[0]);
close(fromdc[1]);
fpout=fdopen(todc[1],"w");
fpin=fdopen(fromdc[0],"r");
if(fpout==NULL||fpin==NULL)
fatal("error convering pipes to streams");
while(printf("tinybc:"),fgets(message,BUFSIZ,stdin)!=NULL){
if(sscanf(message,"%d%[-+*/^]%d",&num1,operation,&num2)!=3){
printf("syntax error\n");
continue;
}
if(fprintf(fpout,"%d\n%d\n%c\np\n",num1,num2,*operation)==EOF)
fatal("Error writing");
fflush(fpout);
if(fgets(message,BUFSIZ,fpin)==NULL)
break;
printf("%d%c%d=%s",num1,*operation,num2,message);
}
fclose(fpout);
fclose(fpin);
}
fatal(char *mess[])
{
fprintf(stderr,"Error:%s\n",mess);
exit(1);
}