#include <stdio.h>
#define BUFSIZE 1024 * 1024

FILE *outfile;
FILE *infile;
unsigned char inbuf[BUFSIZE];

main( int argc, char **argv )
{
    int i;
    
    /* check that there are at least 3 input arguments */
    if (argc < 3)
    {
        fprintf(stderr, "%s: Need at least 2 input arguments!\n", argv[0] );
        fprintf(stderr, "Usage:   %s file1 file2 [ file3 [ file 4 [.... fileN ]  fileout.\n", argv[0] );
        fprintf(stderr, " \t\t bcat concatonates two or more binary files and writes the output to the last filename in the list\n");
        fprintf(stderr, " \t\t if the last file name exists and is not empty return an error\n");
        exit(1);
    }
    
    /* check that we can open output file */
    if ( NULL == (outfile = fopen(argv[argc-1], "ab")) )
    {
        fprintf(stderr, "ERROR %s:  cannot open output file for writing, %s\n", argv[0], argv[argc-1]);
        exit(1);
    }

    /* check that output file is empty */
    fseek(outfile, 0, SEEK_END);
    if ( ftell(outfile) > 0 )
    {
        fprintf(stderr, "ERROR %s:  output file, %s, is not empty\n", argv[0], argv[argc-1]);
        exit(1);        
    }
    
    i = 1;
    /* loop through input files, copying data to output file. */
    while( i < argc - 1 )
    {
        if ( NULL == (infile = fopen(argv[i], "r")) )
        {
            fprintf(stderr, "WARNING %s:  cannot open input file, %s\n", argv[0], argv[i]);        
        }   
        else
        {
            long inbytes, writtenBytes;
            while ( 0 < (inbytes = fread( inbuf, 1, BUFSIZE, infile )) )
            {
                if ( inbytes > (writtenBytes = fwrite( inbuf, 1, inbytes, outfile ) ))
                {
                    fprintf(stderr, "WARNING %s:  error writing data to output file, %s\n", argv[0], argv[i]);                    
                }
            }
            fclose(infile);
        }
        i++;
    }
    
    fclose(outfile);
}