in reply to Re: hexdump -C
in thread hexdump -C

Actually it was solving the problem that the run of \0 lines needs to be replaced by a single '*', not one '*' per every 16 zeroes.

But, as I went to create an example for you, I realized I misunderstood the '*' behavior. It prints one full line of 00 00 00 ... and then the '*' means "repeat the previous line". I'd only ever seen it replace zeroes with '*' because that's the most likely repetition to appear in data files. 

$ perl -E 'say "\0"x64 ."A"x64' | hexdump -C
00000000  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |.........
+.......|
*
00000040  41 41 41 41 41 41 41 41  41 41 41 41 41 41 41 41  |AAAAAAAAA
+AAAAAAA|
*
00000080  0a                                                |.|
00000081

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Combining everyone's ideas, I now get: 

sub hexdump($data) {
  $data =~ s/\G(.{1,16})(\1+)?/
    sprintf "%08X  %-50s|%s|\n%s",
        $-[0],
        "@{[unpack q{(H2)8a0(H2)8},$1]}",
        $1 =~ y{ -~}{.}cr,
        "*\n"x!!$+[2]
  /segr . sprintf "%08X", $+[0]
}

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Re^3: hexdump -C
by harangzsolt33 (Deacon) on Oct 15, 2025 at 14:07 UTC
    That is so cool! I modified it slightly so it also runs on TinyPerl 5.8: 

    sub hexdump
{
  my $s;
  $_[0] =~ s/\G([\0-\xff]{1,16})/ $s = $1; $s =~ y|\x20-\x7e|.|c; spri
+ntf("%08X  %-50s|%s|\n", $-[0], "@{[unpack q{(H2)8a0(H2)8}, $1]}", $s
+);/ge;
  return $_[0];
}

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    I don't understand why I had to do this: ([\0-\xff]{1,16}) instead of (.{16}) This latter one won't capture anything, which is weird. The second thing I don't understand is why this works: 

    "@{[unpack q{(H2)8a0(H2)8}, $1]}"

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      Maybe cause you were missing the /s? (It was also missing in the original code.)

      a0 returns a zero-length string. [ ] creates an anon array and returns a reference to is. @{ ... } is the referenced array. Interpolating an array in a string joins elements with spaces by default.

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        Hmm... interesting! oh yes yes yes, I forgot the /s

        So, once again, here is the working code: 

        #!/usr/bin/perl -w

use strict;
use warnings;

@ARGV = ($0);

print hexdump( join('', <>) );

sub hexdump
{
  my $s;
  $_[0] =~ s/\G(.{1,16})/ $s = $1; $s =~ y|\x20-\x7e|.|c; sprintf("%08
+X  %-50s|%s|\n", $-[0], "@{[unpack q{(H2)8a0(H2)8}, $1]}", $s);/ges;
  return $_[0];
}

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In Section Obfuscated Code