管道--------popen

1. popen出现原因：
创建一个管道连接到另一个进程，然后读其输出或向其输入端发送数据是管道比较常见的操作。
2. 函数原型：
#include
FILE *popen(const char *cmdstring, const char *type);  
返回值：成功返回文件指针，失败返回NULL。
3. 功能作用
  popen调用pipe创建管道，调用fork创建父子进程。子进程执行cmdstring命令后退出，父进程返回fp指针。
3.1 popen(cmdstring,"r")
  

[e-mail]:~/test/pipe>more popen_r.c
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define MAXLINE 256

int main(int argc, char *argv[])
{
    FILE *fp;
    char buf[MAXLINE];
    fp = popen("ls -al","r");

    while(fgets(buf,MAXLINE,fp) != NULL) {
        printf("%s\n",buf);
    }

    return 0;
}

编译运行：
[e-mail]:~/test/pipe>gcc -g popen_r.c -o popen_r
[e-mail]:~/test/pipe>./popen_r
总用量 208

drwxrwxr-x  2 gwwu gwwu  4096 4月  15 15:12 .

drwxr-xr-x 35 gwwu gwwu  4096 4月   9 16:32 ..

-rwxrwxr-x  1 gwwu gwwu  8947 4月  14 09:32 add2

-rw-rw-r-- 1 gwwu gwwu   635 4月  14 09:32 add2.c

-rwxrwxr-x  1 gwwu gwwu 13199 4月  14 10:10 add2_filter

-rw-rw-r-- 1 gwwu gwwu  2041 4月  14 10:10 add2_filter.c

-rw-rw-r-- 1 gwwu gwwu    24 4月  14 16:53 dafadfasd

-rwxrwxr-x  1 gwwu gwwu 13602 4月  14 15:29 fifo

-rwxrwxr-x  1 gwwu gwwu 13603 4月  14 15:29 fifo1

-rw-rw-r-- 1 gwwu gwwu  2074 4月  14 15:27 fifo1.c

-rw-rw-r-- 1 gwwu gwwu  2084 4月  14 15:28 fifo.c

-rwxrwxr-x  1 gwwu gwwu 10472 4月  14 16:43 myuclc

-rw-r--r-- 1 gwwu gwwu   519 4月  14 16:45 myuclc.c

-rwxrwxr-x  1 gwwu gwwu  9748 4月   8 17:42 pipe

-rw-r--r-- 1 gwwu gwwu   702 4月   8 17:42 pipe.c

-rwxrwxr-x  1 gwwu gwwu 12577 4月  13 15:20 pipe_more

-rw-rw-r-- 1 gwwu gwwu  1981 4月  13 15:20 pipe_more.c

-rw-rw-r-- 1 gwwu gwwu  1812 4月   8 10:56 popen.c

-rwxrwxr-x  1 gwwu gwwu 11976 4月  13 17:16 popen_more

-rw-rw-r-- 1 gwwu gwwu  1085 4月  14 09:25 popen_more.c

-rwxrwxr-x  1 gwwu gwwu 10558 4月  14 16:43 popen_pipe

-rw-r--r-- 1 gwwu gwwu   740 4月  14 16:24 popen_pipe.c

-rwxrwxr-x  1 gwwu gwwu  9401 4月  15 15:12 popen_r

-rw-rw-r-- 1 gwwu gwwu   281 4月  15 15:10 popen_r.c

-rwxrwxr-x  1 gwwu gwwu  9542 4月  15 14:57 popen_w

-rw-rw-r-- 1 gwwu gwwu   322 4月  15 14:56 popen_w.c

[e-mail]:~/test/pipe>

3.2 popen(cmdstring,"w")

#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

int main(int argc, char *argv[])
{
    FILE* fp;

    fp = popen("tftp 10.155.3.245","w");

    if(fp == NULL) {
        printf("popen error\n");
        return -1;
    }

    fprintf(fp,"help\n");
    fprintf(fp,"quit\n");
    pclose(fp);
}

编译运行：
[e-mail]:~/test/pipe>./popen_w
tftp> help
tftp-hpa 0.49
Commands may be abbreviated. Commands are:

connect         connect to remote tftp
mode set file transfer mode
put             send file
get receive file
quit exit tftp
verbose         toggle verbose mode
trace           toggle packet tracing
literal         toggle literal mode, ignore ':' in file name
status          show current status
binary set mode to octet
ascii set mode to netascii
rexmt set per-packet transmission timeout
timeout set total retransmission timeout
? print help information
help            print help information
tftp> quit
[e-mail]:~/test/pipe>