Some place:x.x.x.x-x.x.x.x

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

int main (void) {
char str[128];
char *ptr;

strcpy (str, "Some place:x.x.x.x-x.x.x.x");
strtok_r (str, ":", &ptr);

printf ("%s\n", ptr);
return 0;

}

$ ./test       
x.x.x.x-x.x.x.x

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

int main(int argc, char *argv[])
{
  const char prefix[] = "zcat ";
  const char *arg;
  char *strip;
  char *range;
  char *cmd;
  FILE *in;
  char buf[4096];

  if (argc != 2) {
    fprintf(stderr, "Usage: %s file\n", argv[0]);
    return 1;
  }

  arg = argv[1];
  cmd = malloc(sizeof(prefix) + strlen(arg) + 1);
  if (!cmd) {
    fprintf(stderr, "%s: malloc: %s\n", argv[0], strerror(errno));
    return 1;
  }

  sprintf(cmd, "%s%s", prefix, arg);

  in = popen(cmd, "r");
  if (!in) {
    fprintf(stderr, "%s: popen: %s\n", argv[0], strerror(errno));
    return 1;
  }

  while (fscanf(in, "%*s %99[^\n]", buf) == 1){
    strcpy (strip, buf);
    strtok_r (strip, ":", &range);
    printf("%s\n", range);
  }

  if (ferror(in)) {
    fprintf(stderr, "%s: fread: %s\n", argv[0], strerror(errno));
    return 1;
  }
  else if (!feof(in)) {
    fprintf(stderr, "%s: %s: unconsumed input\n", argv[0], argv[1]);
    return 1;
  }

  return 0;
}