I very rarely touch the command line on Windows, I use Linux or Cygwin, but I thought I'd try unpacking from a filehandle wrapped in a do block. Create a file with some unsigned little-endian shorts:-

C:\Users\johngg>perl -Mstrict -Mwarnings -e "print pack q{(S<)*}, 8412
+ .. 8421"
> littleEndian
[download]

Check that the file has the content we expect (Windows is not my natural environment so I drop into Cygwin to use hexdump - is there an equivalent in Windows?):-

$ hexdump -C /cygdrive/c/Users/johngg/littleEndian 
00000000  dc 20 dd 20 de 20 df 20  e0 20 e1 20 e2 20 e3 20  |. . . . .
+ . . . |
00000010  e4 20 e5 20                                       |. . |
00000014
[download]

Now unpack the content:-

C:\Users\johngg>perl -Mstrict -Mwarnings -E "say for unpack q{(S<)*}, 
+do { open
my $fh, q{<:raw}, shift or die $!; <$fh> };" littleEndian
8412
8413
8414
8415
8416
8417
8418
8419
8420
8421
[download]

Using read to pull fixed length records into a buffer for processing is the best way to go but I hope this little aside is of interest.