I meant Capture::Tiny, along the lines of

    ...
    my $session = get_session_id();
    my $cache   = get_cache_handle();
    $cache->set( $session, [ 0, "" ] );           # no data yet
    my $background = go_background( $session );
    ...
    if( not $background->alive ) {
        if( my $data  = $cache->get( $session ) ){
           return show_results( $data );
        }
    }
    ...



sub get_cache_handle {
  use Cache::FileCache;
  return Cache::FileCache->new
  ...
}
[download]

## stuffintocache.pl
#!/usr/bin/perl --
use strict; use warnings;
use Getopt::Long();
use Capture::Tiny qw/ capture /;
Main( @ARGV );
exit( 0 );
sub Main {
    my %opt;
    Getopt::Long::GetOptionsFromArray(
      \@_,
      \%opt,
      'session=s',
      ...
    )
    my($stdout, $stderr, $exit) = capture {
        system( $cmd, @args );
    };
    my $session = get_session_id();
    my $cache   = get_cache_handle();
    $cache->set( $session, [ 1, $stdout, $stderr, $exit ] );
    return;
}
[download]