#include <stdlib.h>
#define GNU_SOURCE
#include <stdio.h>
#include <string.h>

#define gettext(file)\
  getline(&line,0,file);\
  if(i=strlen(line)-1,line[i]=='\n')line[i]=(char)0;

int main(int argc,char **argv){
  FILE *file1,*file2,*tempfile;
  char *line=NULL;
  int i;
  if(argc<3)printf("usage: replace file1 file2\n");
  file1=fopen(argv[1],"r");
  file2=fopen(argv[2],"r");
  tempfile=fopen("tempfile","w");
  while(!feof(file1)){
    gettext(file1);
    if(!strcmp(line,"BB")){
      free(line);line=NULL;
      if(feof(file2)){
        printf("unexpexted EOF in %s\n",argv[2]);
        return 2;
      }
      gettext(file2);
    }
    fputs(line,tempfile);
    putc('\n',tempfile);
    free(line);line=NULL;
  }
  fclose(file1);
  fclose(file2);
  fclose(tempfile);
  remove(argv[1]);
  rename("tempfile",argv[1]);
  return 0;
}