Can someone explain this loop to me? - perl

Question

I have the following Perl code. I Know what the end result is: if I run it and pass in an x9.37 file, it will spit out each field of text. That's great, but I am trying to port this to another language, and I can't read Perl at all. If someone could turn this into some form of pseudocode (I don't need working Java - I can write that part) I just need someone to explain what is going on in the Perl below!
#!/usr/bin/perl -w
use strict;
use Encode;
my $tiff_flag = 0;
my $count = 0;
open(FILE,'<',$ARGV[0]) or die 'Error opening input file';
binmode(FILE) or die 'Error setting binary mode on input file';
while (read (FILE,$_,4)) {
my $rec_len = unpack("N",$_);
die "Bad record length: $rec_len" unless ($rec_len > 0);
read (FILE,$_,$rec_len);
if (substr($_,0,2) eq "\xF5\xF2") {
$_ = substr($_,0,117);
}
print decode ('cp1047', $_) . "\n";
}
close FILE;

Answer 1

read (FILE,$_,4) : read 4 bytes from FILE input stream and load into the variable $_
$rec_len = unpack("N",$_): interpret the first 4 bytes of the variable $_ as an unsigned 32-bit integer in big-endian order, assign to the variable $rec_len
read (FILE,$_,$rec_len): read $rec_len bytes from FILE stream into variable $_
substr($_,0,2): the first two characters of the variable $_
"\xF5\xF2": a two-character string consisting of the bytes 245 and 242
$_ = substr($_,0,117): set $_ to the first 117 characters of $_
use Encode;print decode ('cp1047', $_): interpret the contents of $_ with "code page 1047", i.e., EBCDIC and output to standard output

Answer 2

-w is the old way of enabling warnings.
my declares a lexically scoped variable.
open with < opens a file for reading, the filename is taken from the #ARGV array, i.e. the program's parameters. FILE is the file handle associated with the file.
read reads four bytes into the $_ variable. unpack interprets it as an unsigned 32-bit long (so the following condition can fail only when it's 0).
The next read reads that many bytes to $_ again. substr extracts a substring, and if the first two bytes there are "\xf5\xf2", it shortens the string to the first 117 bytes. It then converts the string to the code page 1047.