pyseek

#!/usr/bin/env python2
# -*- coding: utf-8 -*-

from optparse import OptionParser
parser = OptionParser(usage='%prog [options] [ FROM(MiB) TO(MiB) ... ] PATH',
	description=('Stream given file from/to specified offset.'
		' Limits can be omitted or specified as a single dash for bof/eof.'))
parser.add_option('-b', '--bytes',
	action='store_true', dest='bytes',
	help='Use bytes (B) instead of MiB.')
parser.add_option('-c', '--chunk-size',
	action='store', dest='bs', type='int', metavar='BYTES', default=8192,
	help='Use atomic chunks of a given size for I/O.')
parser.add_option('-f',
	action='store', type='str',
	dest='ch_from', metavar='MiB',
	help='Read stream from this point. Ignored if pairs are given as args.')
parser.add_option('-t',
	action='store', type='str',
	dest='ch_to', metavar='MiB',
	help='Read stream to this point. Ignored if pairs are given as args.')
optz,argz = parser.parse_args()


import itertools as it, operator as op, functools as ft
from cStringIO import StringIO as sio
import os, sys

scale = 1024*1024 if not optz.bytes else 1

src = len(argz) % 2
if not src: parser.error('STDIN processing is not supported')
if len(argz) >= 2:
	chunks = list( (argz[arg], argz[arg+1])
		for arg in xrange(0, len(argz) - src, 2) )
else: chunks = [(optz.ch_from, optz.ch_to)]
src = open(argz[-1]) if src else sys.stdin # not really ;)
dst = sys.stdout # if not optz.buff else sio()

def read(src, dst, chunks, bs):
	for pos,to in chunks:
		try: pos = int(pos)*scale
		except (TypeError, ValueError): pos = 0
		try: to = int(to)*scale
		except (TypeError, ValueError): to = 0

		src.seek(pos, os.SEEK_SET)
		chunk = True
		while chunk:
			chunk = min(to - pos, bs) if to else bs
			chunk = src.read(chunk)
			dst.write(chunk)
			pos += len(chunk)

read(src, dst, chunks, optz.bs)