C将stdout重定向到带有预定义消息的文件 [英] C redirecting stdout to file with predefined message
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问题描述
当我使用dup()和dup2()将案例's'打到案例'f的打开文件时,我想复制在stdout中打印的消息.
I want to duplicate the message that is being printed in stdout when I hit case 's' to the opened file for case 'f' using dup() and dup2().
我不确定dup系统调用的工作方式以及如何将stdout复制到文件中.我知道我必须使用dup捕获stdout指向的内容,然后使用dup2在屏幕和文件之间切换.
I'm not sure how the dup system calls work and how I could dup the stdout to the file. I know I would have to use dup to capture what stdout is pointing at then use dup2 to switch between the screen and the file.
这是我的代码:
#include <stdio.h>
#include <string.h>
#include <fcntl.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <stdlib.h>
#define BUFFER_SIZE 128
#define PERMS 0666
int main(int argc, char *argv[])
{
char outBuffer[BUFFER_SIZE] = "This is a message\n";
int count;
int fd;
char input =0;
int a;
if(argc!=2){
printf("Provide an valid file as an argument\n");
exit(1);
}
if((fd = open(argv[1],O_CREAT|O_WRONLY|O_APPEND,PERMS)) == -1)
{
printf("Could not open file\n");
exit(1);
}
printf("0 to terminate, s to write to stdout, f to write to file\n");
do{
scanf(" %c", &input);
switch(input)
{
case 'f':
case 's':
write(1,outBuffer,strlen(outBuffer));
break;
default:
printf("Invalid Choice\n");
}
}while(input != '0');
close(fd);
return 0;
}
推荐答案
考虑使用"tee"程序(管道到子进程),该程序可以将stdout发送到文件.
Consider using a the 'tee' program (pipe to a child process), which has the ability to send stdout to a file.
case 'f':
pipe fd2[2] ;
pipe(fd2) ;
if ( fork() > 0 ) {
// Child
dup2(fd[0], 0) ;
close(fd[1]) ;
close(
// create command line for 'tee'
char teecmd[256] ;
sprintf(teecmd, "...", ...) ;
execlp(teecmd) ;
} ;
// Parent
fd = fd[1] ;
close(fd[0]) ;
...
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