#!/usr/bin/perl -w
#exec /usr/bin/perl /research-sar/sarexec.pl
use strict;

#starting sar....
if($ARGV[0] eq 'start')
{
 # Checking for correct parameters.. 
 if (exists $ARGV[1] && exists $ARGV[2] && exists $ARGV[3])
 {
   #print "present all things\n";
 }
 else 
 {
  #print "Missing parameters..cant continue..\n";
  
  exit;
 }


my $file_param;
my $file_location;
my $interval;

 $file_param = $ARGV[1];
 $file_location = $ARGV[2];
  open(FH,"> fileloc") or die"cant open the file";
  print FH $file_location or die"cant print to file";
  close(FH) or die "cant close the file";
 $interval = $ARGV[3];
  
   
   
  
my $pid =  fork();
  if($pid==0)
  {
  #print "In child";
  #print "$file_param";

   my $param1;
   open FH,"< $file_param" or die"cant open the file";
   #print "$file_param";
   $param1 = <FH>;
   close FH or die "cant close the file";
   chomp($param1);
   #print $param1;
   #my $testvar="-wWbB";
   system("sar  -o logfile $param1   $interval 0 > /dev/null&");
   exit 0;
  }
  else
  {
  #print "In parent";
  my $exitstatus = wait();
   exit;
  }
}

# stopping sar.....
elsif($ARGV[0] eq 'stop')
{

# Checking for correct parameters.. 
 if (exists $ARGV[1])
 {
   print "Bad parameters cant process\n";
   exit;
 }  
  
  my $loc;
  open FH, "< fileloc" or die " cant open file";
  $loc = <FH> ;
  #print $loc;
  chomp($loc);
  close FH or die "cant close file";
  system("kill \$(pidof sadc)");
  system("sar -f logfile>>$loc");
}

else 
{
  print " Wrong parameters";
}
[download]

Part of your script is still running - that's why ssh doesn't terminate the connection:

...
my $pid =  fork();
...
[download]

You need to detach your child process from the parent process - maybe it's enough to close STDIN and STDOUT, but I'd use Proc::Daemon or what perldoc -q daemon says to start the program detached in the background:

use POSIX qw(setsid);

close STDIN; close STDOUT; close STDERR;
# or better, reopen them into some logfile

setsid();

fork && exit;

# We are now detached from ssh
[download]

#!/usr/bin/perl -w
#exec /usr/bin/perl /research-sar/sarexec.pl
use strict;
[download]

Good! Just as a suggestion on a minor point, try

#!/usr/bin/perl

use strict;
use warnings;
[download]




if($ARGV[0] eq 'start')
{
 # Checking for correct parameters.. 
 if (exists $ARGV[1] && exists $ARGV[2] && exists $ARGV[3])
 {
   #print "present all things\n";
 }
 else 
 {
  #print "Missing parameters..cant continue..\n";
  
  exit;
 }
[download]

In Perl you don't need all those nested conditionals and there are alternatives that may increase readability. In this case you may want to create a start() and a stop() sub, then I'd do:

my %action=(start => \&start, stop => \&stop);
my $todo=shift || '';
die "Wrong parameters\n" unless $action{$todo};
goto $action{$todo};  # a "good" goto;

#
# ...
#

sub $start () {
    die "Missing parameters, can't continue!\n" unless @ARGV==3;
    my ($file_param,$file_location,$interval)=@ARGV;
    # ...
}
[download]




  open(FH,"> fileloc") or die"cant open the file";
[download]

open my $fh, '>', 'fileloc' or die "Can't open `fileloc': $!\n";
[download]




my $pid =  fork();
[download]

Aha! => fork.