#!/bin/ksh
#This shellscript is chopoff.  Chop off the first n bytes from a file.  If the
#file contains less than n bytes, turn it into an empty file.  Write the chopped
#off bytes to the standard output.
#Sample use: chopoff 10 myfile > firsttenbytes

if [[ $# -ne 2 ]]
then
	echo $0: requires exactly 2 command line arguments 1>&2
	exit 1
fi

if [[ ! $1 == +([0-9]) ]]
then
	echo $0: 1st argument $1 must be a non-negative integer 1>&2
	exit 2
fi

if [[ ! -f $2 ]]
then
	echo $0: 2nd argument $2 must be a filename 1>&2
	exit 3
fi

if [[ ! -w $2 ]]
then
	echo $0: need permission to overwrite the file $2 1>&2
	exit 4
fi

/usr/local/bin/head -c$1 $2
/usr/local/bin/tail -c+$(($1 + 1)) $2 > /tmp/$$
mv /tmp/$$ $2
exit 0