#!/usr/bin/env perl

# Execute shell commands and include their output in the current buffer,
# formatted as an indented code block with the original command, in Markdown.
#
# See also: filter-exec-raw for unformatted output without the original
# command.

use strict;
use warnings;
use 5.10.0;

my $startmarker = '<!-- exec -->';
my $endmarker = '<!-- end -->';

my $text;
{
  # line separator:
  local $/ = undef;
  $text = <>;
}

$text =~ s{$startmarker(.*?)$endmarker}{handle_block($1);}egs;

print $text;

sub handle_block {
  my ($block) = @_;

  my $cmd;

  if ($block =~ m/\$ (.*?)$/m) {
    $cmd = $1;
  } else {
    die "bogus cmd";
  }

  my $result = `$cmd`;
  $result =~ s/^/    /gm;

  return "$startmarker\n\n    \$ " . $cmd . "\n" . $result . "\n$endmarker";
}