#!/bin/sh
[ -n "$1" ] || . usage 'file [from [len]]'
file=$1
from=$2
len=$3
if [ -z "$from" ]; then
	cat "$file"
elif [ -z "$len" ]; then
	< "$file" tail -c +$(($from + 1))
else
	< "$file" tail -c +$(($from + 1)) | head -c "$len"
fi