Nagios plugin script not working as expected

I have modified an off-the-shelf Nagios plugin perl script to (in theory) return a one or zero according to the existence, or not, of a file on a remote linux server. The script runs a remote ssh session and logs in as the nagios user. The remote linux servers have private keys setup for that user, and on the bash command line the script works as expected, but when run as a plugin it always returns '1' (true) even if the file does not exist. Some help with the logic or a comment on why things are not working as expected within Nagios would be appreciated. I'd prefer to use this ssh login method rather than having to install nrpe on all the linux servers.

To run from a command line (assuming remote server has a user called nagios with a valid private key):

./check_reboot_required -e ssh -H remote-servers-ip-addr -p 'filename-to-check' -v

Ta.

#! /usr/bin/perl -w
#
#
# License Information:
# This program is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation; either version 2 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program; if not, write to the Free Software
# Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
#
############################################################################

use POSIX;
use strict;
use Getopt::Long;
use lib "/usr/lib/nagios/plugins" ;
use vars qw($host $opt_V $opt_h $opt_v $verbose $PROGNAME $pattern $opt_p $mmin $opt_e $opt_t $opt_H $status $state $msg $msg_q $MAILQ $SHELL $device $used $avail $percent $fs $blocks $CMD $RMTOS);
use utils qw(%ERRORS &print_revision &support &usage );

sub print_help ();
sub print_usage ();
sub process_arguments ();

$ENV{'PATH'}='';
$ENV{'BASH_ENV'}=''; 
$ENV{'ENV'}='';
$PROGNAME = "check_reboot_required";

Getopt::Long::Configure('bundling');
$status = process_arguments();

if ($status){
    print "ERROR: processing arguments\n";
    exit $ERRORS{'UNKNOWN'};
}

$SIG{'ALRM'} = sub {
    print ("ERROR: timed out waiting for $CMD on $host\n");
exit $ERRORS{'WARNING'};
};

$host = $opt_H;
$pattern = $opt_p;

print "Pattern >" . $pattern . "< " if $verbose;
alarm($opt_t);

#$CMD = "/usr/bin/find " . $pattern . " -type f 2>/dev/null| /usr/bin/wc -l";
$CMD = "[ -f " . $pattern . " ] && echo 1 || echo 0";

alarm($opt_t);

## get cmd output from remote system

if (! open (OUTPUT, "$SHELL $host $CMD|" ) ) {
    print "ERROR: could not open $CMD on $host\n";
    exit $ERRORS{'UNKNOWN'};
}

my $perfdata = "";
my $state = "3";
my $msg = "Indeterminate result";
# only first line is relevant in this iteration.
while (<OUTPUT>) {
                my $result = chomp($_);
                $msg = $result;
                print "Shell returned >" . $result . "< length is " . length($result)     . " " if $verbose;
                if ( $result == 1 ) {
                  $msg = "Reboot required (NB: Result still not accurate)" . $result ;
                  $state = $ERRORS{'WARNING'};
                  last;
                } elsif ( $result == 0 ) {
                  $msg = "No reboot required (NB: Result still not accurate) " .    $result ;
              $state = $ERRORS{'OK'};
              last;
            }
            else {
              $msg = "Output received, but it was neither a 1 nor a 0" ;
              last;
            }   

}

close (OUTPUT);
print "$msg | $perfdata\n";
exit $state;

#####################################
#### subs


sub process_arguments(){
    GetOptions
        ("V"   => \$opt_V, "version"    => \$opt_V,
         "v"   => \$opt_v, "verbose"    => \$opt_v,
         "h"   => \$opt_h, "help"   => \$opt_h,
         "e=s" => \$opt_e, "shell=s"    => \$opt_e,
             "p=s" => \$opt_p, "pattern=s"  => \$opt_p,
         "t=i" => \$opt_t, "timeout=i"  => \$opt_t,
         "H=s" => \$opt_H, "hostname=s" => \$opt_H
     );

if ($opt_V) {
    print_revision($PROGNAME,'$Revision: 1.0 $ ');
    exit $ERRORS{'OK'};
}

if ($opt_h) {
    print_help();
    exit $ERRORS{'OK'};
}

if (defined $opt_v ){
    $verbose = $opt_v;
}

    if (defined $opt_e ){
    if ( $opt_e eq "ssh" ) {
        if (-x "/usr/local/bin/ssh") {
        $SHELL = "/usr/local/bin/ssh";
        } elsif ( -x "/usr/bin/ssh" ) {
        $SHELL = "/usr/bin/ssh"; 
        } else {
                    print_usage();
                    exit $ERRORS{'UNKNOWN'};
                }

    } elsif ( $opt_e eq "rsh" ) {
        $SHELL = "/usr/bin/rsh";
    } else {
        print_usage();
                exit $ERRORS{'UNKNOWN'};
    }
    } else {
   print_usage();
       exit $ERRORS{'UNKNOWN'};
}

unless (defined $opt_t) {
    $opt_t = $utils::TIMEOUT ;  # default timeout
}

unless (defined $opt_H) {
    print_usage();
    exit $ERRORS{'UNKNOWN'};
}


return $ERRORS{'OK'};
}

sub print_usage () {
    print "Usage: $PROGNAME -e <shell> -H <hostname> -p <directory/file pattern> [-t <timeout>] [-v verbose]\n";
}

sub print_help () {
print_revision($PROGNAME,'$Revision: 0.1 $');
print "\n";
print_usage();
print "\n";
print "   Checks for the presence of a 'reboot-required' file on a remote host via SSH or RSH\n";
print "-e (--shell)     = ssh or rsh (required)\n";
print "-H (--hostname)  = remote server name (required)";
print "-p (--pattern)   = File pattern for find command (default = /var/run/reboot-required)\n";
print "-t (--timeout)   = Plugin timeout in seconds (default = $utils::TIMEOUT)\n";
print "-h (--help)\n";
print "-V (--version)\n";
print "-v (--verbose)   = debugging output\n";
print "\n\n";
support();
}