//實用工具程序之一，作用是在將消息轉發給相關程序前預處理這些消息

#include "fd.h"#include "sgetopt.h"#include "readwrite.h"#include "strerr.h"#include "substdio.h"#include "exit.h"#include "fork.h"#include "wait.h"#include "env.h"#include "sig.h"#include "error.h"#define FATAL "preline: fatal: "void die_usage(){  strerr_die1x(100,"preline: usage: preline cmd [ arg ... ]");}int flagufline = 1; char *ufline;int flagrpline = 1; char *rpline;int flagdtline = 1; char *dtline;char outbuf[SUBSTDIO_OUTSIZE];char inbuf[SUBSTDIO_INSIZE];substdio ssout = SUBSTDIO_FDBUF(write,1,outbuf,sizeof outbuf);substdio ssin = SUBSTDIO_FDBUF(read,0,inbuf,sizeof inbuf);void main(argc,argv)int argc;char **argv;{  int opt;  int pi[2];  int pid;  int wstat;   sig_pipeignore();   if (!(ufline = env_get("UFLINE"))) die_usage();  if (!(rpline = env_get("RPLINE"))) die_usage();  if (!(dtline = env_get("DTLINE"))) die_usage();   while ((opt = getopt(argc,argv,"frdFRD")) != opteof)    switch(opt) {      case 'f': flagufline = 0; break;      case 'r': flagrpline = 0; break;      case 'd': flagdtline = 0; break;      case 'F': flagufline = 1; break;      case 'R': flagrpline = 1; break;      case 'D': flagdtline = 1; break;      default: die_usage();    }  argc -= optind;  argv += optind;  if (!*argv) die_usage();   if (pipe(pi) == -1)    strerr_die2sys(111,FATAL,"unable to create pipe: ");  pid = fork();  if (pid == -1)    strerr_die2sys(111,FATAL,"unable to fork: ");  if (pid == 0) {    close(pi[1]);    if (fd_move(0,pi[0]) == -1)      strerr_die2sys(111,FATAL,"unable to set up fds: ");    sig_pipedefault();    execvp(*argv,argv);    strerr_die4sys(error_temp(errno) ? 111 : 100,FATAL,"unable to run ",*argv,": ");  }  close(pi[0]);  if (fd_move(1,pi[1]) == -1)    strerr_die2sys(111,FATAL,"unable to set up fds: ");   if (flagufline) substdio_bputs(&ssout,ufline);  if (flagrpline) substdio_bputs(&ssout,rpline);  if (flagdtline) substdio_bputs(&ssout,dtline);  if (substdio_copy(&ssout,&ssin) != 0)    strerr_die2sys(111,FATAL,"unable to copy input: ");  substdio_flush(&ssout);  close(1);   if (wait_pid(&wstat,pid) == -1)    strerr_die2sys(111,FATAL,"wait failed: ");  if (wait_crashed(wstat))    strerr_die2x(111,FATAL,"child crashed");  _exit(wait_exitcode(wstat));}