/*
Program: EXTRACT.C
Author : Kim Moser
Date   : 02/15/89
System : IBM PC / Borland Turbo-C 2.0
Descrip: Extracts a run of bytes from a specified file to stdout

Usage  :
	EXTRACT [-<flags>] [-]<offset> <length>
*/

#include <stdlib.h>
#include <stdio.h>
#include <fcntl.h>
#include <io.h>
#include <ctype.h>  /* isalpha */

int MSG=1, WARN=1;  /* Whether to print messages and warnings */

void usage(void)
{
	if (!MSG) return;
	fprintf( stderr, "EXTRACT  v1.0 (2/15/89)  Copyright (c) Kim Moser  All Rights Reserved\n" );
	fprintf( stderr, "Usage: EXTRACT [-<switches>] <offset> <length>\n\n" );
	fprintf( stderr, "  Starting at byte <offset> of stdin, extracts <length> bytes to stdout.\n" );
	fprintf( stderr, "  If offset < 0 then offset is taken to be from EOF.\n\n" );
	fprintf( stderr, "  SWITCH  MEANING\n" );
	fprintf( stderr, "  M       suppress messages\n" );
	fprintf( stderr, "  W       suppress warnings\n" );
	exit(1);
}

void main(argc, argv)
int argc;
char **argv;
{
	unsigned long int offset, length, i;
	int ch;
	int fromend=0;  /* Whether offset should be calculated from EOF */
	long flen;
	int j=1, k;

	if (argc==1) usage();
	if ( (argv[j][0]=='-') && isalpha(argv[j][1]) ) {
		for (k=1; argv[j][k]; k++)
			switch(argv[j][k]) {
				case 'M':  /* Suppress msgs */
					MSG=0;
					break;
				case 'W':  /* Suppress warnings */
					WARN=0;
					break;
				default:
					usage();
					break;
			}
		j++;  /* Point to param which should contain offset */
	}

	fromend = (argv[j][0]=='-' ? 1 : 0);
	if (!sscanf(&argv[j][fromend], "%lu", &offset)) usage();
	if (argv[j+1]==NULL) usage();
	if (!sscanf(argv[j+1], "%lu", &length)) usage();

	if (setmode(fileno(stdin), O_BINARY)==-1) {
		if (WARN)
			fprintf( stderr, "Error setting mode of stdin to O_BINARY.\n" );
		exit(1);
	}
	if (setmode(fileno(stdout), O_BINARY)==-1) {
		if (WARN)
			fprintf( stderr, "Error setting mode of stdout to O_BINARY.\n" );
		exit(1);
	}

	if (fromend) {
		if ((flen=filelength(fileno(stdin)))==-1) {
			if (WARN)
				fprintf( stderr, "Error finding length of stdin.\n" );
			exit(1);
		}
		/* Check if they wanted to begin before beginning: */
		if (flen < offset+1) {
			if (WARN)
				fprintf( stderr, "Offset from EOF (-%lu) is larger than file length (%lu).\n", offset, flen );
			exit(1);
		}
		if (MSG)
			fprintf( stderr, "Offset from end: -%lu (%lu from beginning).\n", offset, flen-offset-1 );
		if ( fseek(stdin, (long) (flen-offset-1), SEEK_SET) ) {
			if (WARN)
				fprintf( stderr, "Unable to set stdin file pointer to -%lu (%lu from beginning).\n", offset, flen-offset-1 );
			exit(1);
		}
	} else {
		if ( fseek(stdin, offset, SEEK_SET) ) {
			if (WARN)
				fprintf( stderr, "Unable to set stdin file pointer to %lu.\n", offset );
			exit(1);
		}
	}

	for (i=0; i<length; i++) {
		if ( ((putchar(ch=getchar()))==EOF) || (ch==EOF) ) break;
	}

	if (i<length)
		if (WARN)
			fprintf( stderr, "\nWent past end of input file by %lu bytes.\n", length-i );
}