A simple implementation of the Linux `truncate` function - this is missing in Mac OSX so I decided to implement it. The binary is a Release build for Mac OSX 10.8.4; should run in most versions.

truncate.cpp

/*
 * truncate.cpp
 *
 *  Created on: Sep 4, 2013
 *      Author: marco
 */

#include <iostream>
#include <stdio.h>
#include <unistd.h>


using namespace std;

// Prints usage for this application
void usage() {
    cout << "Usage: truncate [-s SIZE] file" << endl;
    cout << endl << "\tSIZE in bytes is the desired size for the file,"
            " 0 by default" << endl;
}

// This is a super-simplified implementation of Linux's `truncate` bash
// functionality - it only supports the -s SIZE argument.
//
// Use with care: if the argument following the -s cannot be parsed into a valid
// integer format, it will truncate the file to 0 bytes
int main(int argc, char* argv[]) {
    if (argc < 2) {
        usage();
        exit(1);
    }
    long size = 0;
    int file_index = 1;
    if (strcmp(argv[1], "-s") == 0) {
        size = atol(argv[2]);
        file_index = 3;
    }
    char *fname = argv[file_index];
    cout << "Truncating " << fname << " to " << size << " bytes length" << endl;
    if (truncate(fname, size) != 0) {
        cerr << "Could not truncate file " << fname << " to " << size << " bytes" << endl;
        exit(1);
    }
}