How can I parse space separated by six STDIN lines unpacked in Perl?

Question

I have a Java program that splashes in hexadecimal format, separated by spaces, 16 bytes of raw packet received over the network. Since I do not want to change this code, I am passing the result to a Perl script, which theoretically can simply unpack from STDIN variables. The following is an example of entering a string in a Perl file:

  FF FF 09 7D 10 01 07 01 00 02 00 1D 00 00 00 00 00 06 06 00 07 00 
 | --garbage ----- | c-- | c-- | int --- | int --- | int --- | int --- | int --- | int --- | int- - |

(c for char / byte, int for 16-bit integer variable)

At first I wanted to use unpack to cleanly separate each line of input from the variables that I need. However, due to a space in the line, I'm not sure how to handle it (I can use "A" as a template, but then I could just use split!)

Is there an elegant way to use unpack() ? I am not a Perl master, but as I said earlier, use split , and then manually convert each hex to byte, and then use bit manipulation and masks to get what I want. Any other suggestions (if unpack doesn't save the day)?

Answer 1

Assuming these ints are in big-endian order, use

 #! /usr/bin/perl use warnings; use strict; # for demo only *ARGV = *DATA; while (<>) { my @fields = unpack "x5C2n7", pack "C*", map hex, split; print "[", join("][" => @fields), "]\n"; } __DATA__ FF FF 09 7D 10 01 07 01 00 02 00 1D 00 00 00 00 00 06 00 07 00 

It starts with packing in bytes ( C* ) according to their values. The unpack template has the following parts:

• x5 skips five bytes
• C2 decodes two unsigned char values
• n7 decodes seven 16-bit unsigned integers

Output:

  $ ./dump-packets
 [1] [7] [256] [512] [7424] [0] [0] [1536] [1792] 

Answer 2

If you want to use decompression for decompressed data, you first need to pack it first. And you will need to remove the spaces before you do this.

In other words,

 $line =~ tr/ //d; # remove spaces $line = pack 'H*', $line; # convert hex to binary # Now you can use unpack.