C - プロセス間通信 - お話は楽しい(パイプ、pipe関数)

Head First C
原著

開発環境

• OS: macOS High Sierra - Apple
• Text Editor: Emacs
• コンパイラー: LLVM/Clang, GCC(gcc)
• プログラミング言語: C

Head First C ―頭とからだで覚えるCの基本 (David Griffiths (著)、Dawn Griffiths (著)、中田 秀基 (監修)、木下 哲也 (翻訳)、オライリージャパン)の10章(プロセス間通信 - お話は楽しい)、エクササイズ(p. 447)を取り組んでみる。

エクササイズ(p. 447)

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

void error(char *msg) {
  fprintf(stderr, "%s: %s\n", msg, strerror(errno));
  exit(1);
}

void open_url(char *url) {
  char launch[255];
  sprintf(launch, "open '%s'", url);
  system(launch);
}

int main(int argc, char *argv[]) {
  char *phrase = argv[1];
  char *vars[] = {"RSS_FEED=http://rss.cnn.com/rss/edition.rss", NULL};
  int fd[2];
  if (pipe(fd) == -1) {
    error("パイプを作成できません");
  }
  pid_t pid = fork();
  if (pid == -1) {
    error("プロセスをフォークできません");
  }
  if (!pid) {
    close(fd[0]);
    dup2(fd[1], 1);
    if (execle("/usr/bin/python", "/usr/bin/python", "rssgossip.py", "-u",
               phrase, NULL, vars) == -1) {
      error("スクリプトを実行できません");
    }
  }
  close(fd[1]);
  dup2(fd[0], 0);
  char line[255];
  for (; fgets(line, 255, stdin);) {
    printf("%s", line);
    if (line[0] == '\t') {
      open_url(line + 1);
    }
  }
}

入出力結果(Terminal)

$ cc sample.c -o sample
$ ./sample US
US offers Libya as model for North Korea talks
 https://www.cnn.com/2018/04/30/asia/north-korea-bolton-libya-intl/index.html
Sajid Javid named new UK home secretary after Windrush scandal
 https://www.cnn.com/2018/04/30/europe/sajid-javid-uk-new-home-secretary-intl/index.html
The 57 most outlandish, outrageous and offensive lines from Trump's Michigan rally
 https://www.cnn.com/2018/04/30/politics/donald-trump-michigan-speech-annotation/index.html
Iran accuses US of breaching nuclear deal as Macron fights to save it
 https://www.cnn.com/2018/04/30/asia/rouhani-macron-iran-deal-intl/index.html
Migrant caravan reaches US-Mexico border
 https://www.cnn.com/2018/04/29/americas/migrant-caravan-us-border-crossing/index.html
US ready to pull out of Iran deal, top diplomat says
 https://www.cnn.com/2018/04/29/politics/pompeo-iran-nuclear-deal-intl/index.html
US mobile carriers agree to merge
 http://money.cnn.com/2018/04/29/news/companies/t-mobile-sprint-merger/index.html
Trump slams 'lousy' London embassy again
 https://www.cnn.com/2018/04/29/politics/trump-london-embassy-lousy-intl/index.html
3 US Marines charged with rape
 https://www.cnn.com/2018/04/29/us/marines-charged-with-rape/index.html
Superstitions of rich and famous
 https://www.cnn.com/style/article/strange-habits-creative-people-beyonce-benjamin-franklin/index.html
Intelligence: US raises monitoring before Trump-Kim summit
 https://www.cnn.com/2018/04/29/politics/us-north-korea-intelligence/index.html
Top Australian financial firm is in crisis
 http://money.cnn.com/2018/04/30/news/companies/amp-australia-scandal-catherine-brenner/index.html
Who is Meghan Markle's future husband?
 https://www.cnn.com/2018/04/28/europe/prince-harry-chris-jackson-intl/index.html
Miller and Sokolsky: As Pompeo's star rises, Haley and Kushner risk getting eclipsed
 https://www.cnn.com/2018/04/29/opinions/pompeo-star-rises-eclipsing-kushner-haley-opinion-miller/index.html
Don Lincoln: This satellite gave us a new star map that is out of this world
 https://www.cnn.com/2018/04/28/opinions/gaia-star-map-opinion-lincoln/index.html
$