in reply to hexdump -C

The use of (?{}) doesn't help. 

s/\G(?|(\0{16})+(?{'*'})|(.{1,16})(?{...}))/$^R\n/sgr  What you used.
s/\G(\0{16})|\G.{1,16}/($1?"*":...)."\n"/segr          Could be used.
s/\G.{1,16}/($&eq"\0"x16?"*":...)."\n"/segr            What I used.

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Combining this change and tybalt89's changes, we get 

#!/usr/bin/perl

use v5.36;
use Path::Tiny qw( path );

sub hexdump( $data ) {
   $data =~ s/\G.{1,16}/ 
      ( $& eq "\0"x16
      ? "*"
      : sprintf "%08X  %-50s|%s|",
           $-[0],
           "@{[unpack q{(H2)8a0(H2)8}, $&]}",
            $& =~ y{ -~}{.}cr
      ) . "\n"
   /segr . sprintf "%08x\n", length $data
}

print hexdump( path( $0 )->slurp );

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Re^2: hexdump -C
by NERDVANA (Priest) on Oct 14, 2025 at 05:15 UTC
    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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      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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In Section Obfuscated Code