use strict;
use warnings;

use File::Temp qw/ tempfile /;

# Initially, borrowed bits from IPC::Run3 for capturing STDERR.
# Then, made efficient for lesser overhead than Capture::Tiny.

sub do_cmd {
  my ( $cmd ) = @_;
  my ( undef, $err_file ) = tempfile();
  my ( $err, $err_fh, @result ) = ('');

  if ( $^O eq 'MSWin32' ) {
    # this is one way to capture STDERR, also works on Unix
    open my $cmd_fh, "$cmd 2> $err_file |" or die "$!\n";
    @result = <$cmd_fh> if defined ( fileno $cmd_fh );
    close $cmd_fh;
  }
  else {
    # this is another way, but not supported on Windows
    local *STDERR_SAVE;

    open STDERR_SAVE, '>&STDERR';
    open $err_fh, '+>', $err_file;
    binmode $err_fh, ':raw';
    open STDERR, '>&' . fileno $err_fh;

    open my $cmd_fh, "$cmd |" or die "$!\n";
    @result = <$cmd_fh> if defined ( fileno $cmd_fh );
    close $cmd_fh;

    open STDERR, '>&STDERR_SAVE';
    close $err_fh;
  }

  if ( -s $err_file ) {
    open $err_fh, '<', $err_file;
    local $/ = undef; $err = <$err_fh>;
    close $err_fh;
  }

  unlink $err_file;

  return ( $err, @result );
}

# Demonstration.

my $pass = 'password';
my $ip   = 'ip_address';
my $cmd  = 'uptime';

my ($err, @result) = do_cmd("sshpass -p $pass ssh user\@$ip $cmd");

if (length $err) {
  print "ERROR: $err\n";
} else {
  chomp @result;
}