You forgot to include stdio.h for printf, etc, which is a crash-causing error in 64-bit programs.

Most major problem:

Code:

char *strip;

...

strcpy(strip,buf);

You use strip without giving it any sort of valid pointer like what you did with cmd and malloc, or just giving it contents from the start, like buf.

There's no point copying it either, use buf directly.

There's also no point making your program more complicated with strtok_r for a program this simple.

You also forgot error checking after calling strtok, which would be a crash-causing error for any line not containing :

Also, while that's a clever use of scanf but there's a built-in function which does that faster and more simply called fgets.

Also, you forgot to call pclose when the program's done, which can cause zombie processes.

Also, prefix should be a define, not a variable. (What that really does is copy from a constant array into a non-constant one at runtime. Using a #define, or just a "" string, just uses the original source.)

Also, never use sizeof() to determine the lengths of strings. That worked by pure coincidence here, since you put it in an array of content-defined length, but that will surprise you in some contexts. sizeof(buf) would always be 4096. sizeof(cmd) would either be 4(32-bit systems) or 8(64-bit systems). strlen() avoids that ambiguity.

Code:

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

#define PREFIX "zcat "

int main(int argc, char *argv[])
{
  const char *arg;
  char *cmd, buf[4096];
  FILE *in;

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

  arg = argv[1];
  cmd = malloc(strlen(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(fgets(buf, 4096, in)) {
    char *tok=strtok(buf, ":"); // First token, 'place'
    // Second token, 'xxx-xxx'
    if(tok != NULL) tok=strtok(NULL, ":");
    // If anything was found, print it
    if(tok != NULL) printf("%s", tok);
  }

  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;
  }

  pclose(in);

  return 0;
}

This is a much easier shell script than a C program, by the way.

Code:

#!/bin/sh

zcat "$@" | awk -F: '$2 { print $2 }'