Depending on the exact format of your text file you may be able to reduce the code to something like this ;

#!perl
use strict;
open FH_SECOND,"<",$ARGV[0] or die $!;            

my @setting = ('Port Speed','Duplex Setting','Switchport Access Mode',
+'Spanning Tree Mode');
my $line1 = <FH_SECOND>;
if ($line1 =~ /description xxxxxxxxx/){
  while (<FH_SECOND>){ 
    my $msg = 'Gigabit '.shift @setting;
    if(/speed 1000|duplex full|switchport mode access|spanning-tree po
+rtfast/){ 
      print $msg." is OK!!!\n";
    } else {
      print $msg." is WRONG!!!\n";
    }
  }  
} else {
  print "The Configuration File $ARGV[0] is NOT the RIGHT FILE \n";
}
close(FH_SECOND);  

# test file
#description xxxxxxxxx
#speed 1000
#duplex full
#switchport mode access
#spanning-tree portfast
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poj