Perl converting binary stream to hex

Question

The problem I am having is when I have a Perl script reading data (PE Executable) via STDIN and the stream contains a line terminator "0A" the conversion to hex misses it. Then when I convert the hex data back it is corrupted (missing 0A in the hex format). So how can I detect the "windows" version of line feed "0A" in Perl?

Note: Linux OS (Perl) is reading a Windows PE

!usr/bin/perl

while($line = <STDIN>)
{
    chomp($line);
    @bytes = split //, $line;
    foreach (@bytes)
    {
        printf "%02lx", ord $_;
    }
}

Usage example:

[root@mybox test]# cat test.exe | perl encoder.pl > output

Eric Strom · Accepted Answer · 2010-11-23 21:18:40Z

6

In your loop, you are running chomp on each input line. This is removing whatever value is currently in $/ from the end of your line. Chances are this is 0x0a, and that's where the value is going. Try removing chomp($line) from your loop.

In general, using line oriented reading doesn't make sense for binary files that are themselves not line oriented. You should take a look at the lower level read function which allows you to read a block of bytes from the file without caring what those bytes are. You can then process your data in blocks instead of lines.

answered Nov 23, 2010 at 21:18

Eric Strom

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6 Comments

Jim Davis Over a year ago

Wow, that's embarrassing. I dove straight into messing with binmode() and didn't even see the chomp.

cjm Over a year ago

Also, you'll find unpack('H*', $binary_string) is much more efficient than split and printf '%02x'.

ekronnenburg Over a year ago

made a change#!/usr/bin/perl binmode(STDIN); while(<STDIN>) { #print $_; push(@bytes,$_); } foreach (@bytes) { printf "%02lx", ord $_; }

ekronnenburg Over a year ago

With the code change to binmod + removing chomp the stream is breaking

ekronnenburg Over a year ago

Verified chomp is removing the 0a from the encoding stream however I need to insert the following charachters '\x' per hex set eg 0d0d0a24 would be \x0d\x0d\x0a\x24 any suggestions how to do this would be appreciated.

|

ph1g · Accepted Answer · 2011-04-08 03:22:11Z

1

#With split
cat magic.exe | perl -e 'print join("", map { sprintf("\\x%02x", ord($_)) } split(//, join("", <STDIN>)))' > hex_encoded_binary

#With pack
cat magic.exe| perl -e 'print join("", map { "\\x" . $_ } unpack("H*", join("", <STDIN>)) =~ /.{2}/gs)' > hex_encoded_binary

answered Apr 8, 2011 at 3:22

ph1g

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