#!/usr/bin/perl
use strict;
use warnings;

# peekFile
# This script displays the values of the bytes at specified offsets
# in a specified file.
# The name 'peekFile' is supposed to suggest the 'peek' command of BASIC
# The first command-line arg is the name of the file to be used
# The remaining args supplies an array of offsets
# For example:
# peekFile myDataFile 53 105
# would print out the value of the bytes at offsets 53 and 105
# Offsets can be given in decimal, octal, or hexadecimal

# Cameron Hayne (macdev@hayne.net)  August 2006

my $scriptName = "peekFile";
if (scalar(@ARGV) < 2)
{
    die "Usage: $scriptName filename offset1 [offset2 ...]\n";
}

my $verbose = 1;
my $filename = shift @ARGV;
my @offsets = @ARGV;

sub convertToDec($)
{
    my ($value) = @_;

    if ($value =~ /^0/)
    {
        return oct($value); # does both oct and hex
    }
    else
    {
        return $value;
    }
}

use Fcntl qw(:seek);
open(FILE, "<$filename") or die "Can't open file $filename: $!\n";
foreach my $offset (@offsets)
{
    my $decOffset = convertToDec($offset);

    seek(FILE, $decOffset, SEEK_SET) or die "seek failed: $!";
    my $numBytesToRead = 1;
    my $value;
    read(FILE, $value, $numBytesToRead) == $numBytesToRead
         or die "read failed: $!";
    printf("Offset $offset: 0x%x\n", unpack("C", $value));
}
close(FILE);