#!/usr/bin/perl -w
#exec /usr/bin/perl /research-sar/sarexec.pl
use strict;
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Good! Just as a suggestion on a minor point, try

#!/usr/bin/perl

use strict;
use warnings;
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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;
 }
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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;
    # ...
}
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  open(FH,"> fileloc") or die"cant open the file";
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open my $fh, '>', 'fileloc' or die "Can't open `fileloc': $!\n";
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my $pid =  fork();
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Aha! => fork.