0901假設存在一個可以從標準輸入讀入字母并且將其從小寫轉換為大寫輸出的可執行程序upcase

/*

• 假設存在一個可以從標準輸入讀入字母并且將其從小寫轉換為大寫輸出的可執行程序upcase,
• 使用pipe函數編寫一個應用程序，實現將一個指定文本文件中的字母都轉換為大寫。
  */

#include <stdio.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/wait.h>

#define BUFSIZE PIPE_BUF

int main(int argc, char argv[])
{
int n,fd[2];
pid_t pid;
char buffer[BUFSIZE+1];
FILE fp;
if(argc<=1)
{
printf("usage:%s <pathname>\n",argv[0]);
exit(1);
}
//open txt file
if((fp=fopen(argv[1],"r"))==NULL)
{
printf("Can't open %s\n",argv[1]);
exit(1);
}
//create pipe
if(pipe(fd)<0)
{
printf("pipe failed!\n");
exit(1);
}
//create son process
if((pid=fork())<0)
{
printf("fork failed!\n");
exit(1);
}
else if(pid>0)// father process
{
close(fd[0]);
while(fgets(buffer,BUFSIZE,fp)!=NULL)
{
n=strlen(buffer);
//write data to pipe
if(write(fd[1],buffer,n)!=n)
{
printf("write error to pipe.\n");
exit(1);
}
}
if(ferror(fp))
{
printf("fgets error.\n");
exit(1);
}
close(fd[1]);
if(waitpid(pid,NULL,0)<0)
{
printf("waitpid error!\n");
exit(1);
}
exit(0);
}
else
{
close(fd[1]);
if(fd[0]!=STDIN_FILENO)
{
//copy pipe to stdin
if(dup2(fd[0],STDIN_FILENO)!=STDIN_FILENO)
{
printf("dup2 error to stdin!\n");
exit(1);
}
close(fd[0]);
}
//run user program
if(execl("upcase","upcase",(char *)0)<0)
{
printf("execl error for upcase.\n");
exit(1);
}
exit(0);
}
//return 0;
}