linux下popen函数用法代码

linux下popen函数用法代码

// linux下popen函数用法代码：zread.c，摘自gzip例子
#include <stdio.h> 
#include <stdlib.h> 
#include <string.h> 
 
/* Trivial example of reading a gzip'ed file or gzip'ed standard input 
 * using stdio functions fread(), getc(), etc... fseek() is not supported. 
 * Modify according to your needs. You can easily construct the symmetric 
 * zwrite program. 
 * 
 * Usage: zread [file[.gz]] 
 * This programs assumes that gzip is somewhere in your path. 
 */ 
int main(argc, argv) 
    int argc; 
    char **argv; 
{ 
    FILE *infile; 
    char cmd[256]; 
    char buf[BUFSIZ]; 
    int n; 
 
    if (argc < 1 || argc > 2) { 
        fprintf(stderr, "usage: %s [file[.gz]]\n", argv[0]); 
        exit(EXIT_FAILURE); 
    } 
    strcpy(cmd, "gzip -dc ");  /* use "gzip -c" for zwrite */ 
    if (argc == 2) { 
        strncat(cmd, argv[1], sizeof(cmd)-strlen(cmd)); 
    } 
    infile = popen(cmd, "r");  /* use "w" for zwrite */ 
    if (infile == NULL) { 
        fprintf(stderr, "%s: popen('%s', 'r') failed\n", argv[0], cmd); 
        exit(EXIT_FAILURE); 
    } 
    /* Read one byte using getc: */ 
    n = getc(infile); 
    if (n == EOF) { 
        pclose(infile); 
        exit(EXIT_SUCCESS); 
    } 
    putchar(n); 
 
    /* Read the rest using fread: */ 
    for (;;) { 
        n = fread(buf, 1, BUFSIZ, infile); 
        if (n <= 0) break; 
        fwrite(buf, 1, n, stdout); 
    } 
    if (pclose(infile) != 0) { 
        fprintf(stderr, "%s: pclose failed\n", argv[0]); 
        exit(EXIT_FAILURE); 
    } 
    exit(EXIT_SUCCESS); 
    return 0; /* just to make compiler happy */ 
} 

zread abc.tar.gz
会输出 abc.tar.gz文件的内容

相当于执行: gzip -dc abc.tar.gz

abc.tar.gz 的由来，存在一个文本文件 hello.c
tar zcvf abc.tar.gz hello.c

例子2

python代码 ，看怎么转换为linux c 代码

# -*- coding: utf8 -*-
import sys
import time
import threading
from pywebsocketserver.server import SocketServer
from pywebsocketserver.baseio import BaseIO
import subprocess
def tcpdump():  
    global g_output_log
    popen=subprocess.Popen([‘bash’,‘-c’,“/usr/sbin/tcpdump -i eth0 -v”],stdout=subprocess.PIPE,stderr=subprocess.PIPE)
    pid=popen.pid
    print(‘Popen.pid:’+str(pid))  
    while True:  
        line=popen.stdout.readline().strip()
        #line =popen.communicate()
        print “output:%s” %(line)
        g_output_log.append(line)
        if subprocess.Popen.poll(popen) is not None:  
                break
    print(‘DONE’)  
    
class MyIO(BaseIO):
    def onData(self,uid,text):
        self.sendData(uid,“received the message：%s”%(text,))
    def onConnect(self,uid):
        global g_uid
        g_uid=uid
        while True:
            #self.sendData(uid,”testing…”)
            if  len(g_output_log) >0:
                log = g_output_log.pop()
                self.sendData(uid,log)
            else:
                time.sleep(.01)
try:
    g_output_log=[]
    g_uid=None
    tcpdump = threading.Thread(name=‘tcpdump’, target=tcpdump)
    tcpdump.start()        
    port = sys.argv[1]
except:
    port = 88
port = int(port)
myIo = MyIO()
SocketServer(port,myIo).run()    

备注

FILE *tcpdump = popen(“tcpdump -s0 -w - 2>/dev/null”, “r”);

redirect stderr to /dev/null:

FILE *tcpdump = popen(“tcpdump -s0 -w - 2>/dev/null”, “r”);
2>&1 means to redirect stderr to stdout, 2>file means to redirect stderr to file (and redirecting to /dev/null essentially ignores the output)