#!/usr/bin/env perl

# Execute shell commands with the included block passed to their stdin.
#
# I haven't wound up using this much, but in principle it has some
# applications.
#
# See also: filter-exec, filter-exec-raw.

use strict;
use warnings;
use 5.10.0;

use IPC::Cmd qw(can_run run_forked);

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

$text =~ s{
  <!--[ ]exec-stdin[ ](.*?)[ ]-->\n
  (.*?)\n
  <!--[ ]end[ ]-->
}{
  handle_block($1, $2);
}egsx;

print $text;

sub handle_block {
  my ($command, $input) = @_;

  my $output_text = '';

  my $result = run_forked($command, {
    child_stdin    => $input,
    timeout        => 300,
    stdout_handler => sub { $output_text .= $_[0]; },
    stderr_handler => sub { $output_text .= $_[0]; }
  });

  # Kill any trailing newlines so that the output will fit between markers
  # without adding a blank line (something about this will probably lead to
  # bugs eventually):
  chomp($output_text);

  my $starter = 'exec-stdin';
  return "<!-- $starter $command -->\n$output_text\n<!-- end -->";
}

__DATA__
A self-test - add some numbers and use ,r in vim to check:

<!-- exec-stdin sort -n -->
1
2
8
9
10
<!-- end -->