Shell Programming and Scripting

my @array_parent = (Some inegers);
my $outputfile = 'output.txt';
my $master_file = 'master.txt';
open (MASTER,"$>>master.txt"); # where exactly you are using this file handler ?? you opened the file in append mode but never actually writing on file handler 
foreach my $child (@array_parent){
        chomp ( my $line = `grep "$child" "$outputfile"` ) ;
        # chomp($line);
        chomp($child);
        my @match = grep (/$child/i, @array_parent_level1); # where is this array defined ??
        if ($child == 22105201 ){
              Lookup($line,*MASTER,$outputfile);
        }
}
close(OUT);
close(MASTER);

sub Lookup {
        my ($line,$MASTER,$outputfile)= @_;
        my ($parent,$len);
        open (OUT,"<$outputfile") or die "Can't OPen File $outputfile"; # Read the file in an array before sending it to function and pass the reference of array here .. so even if you call this function 100 times or 1 time you will do file I/O only once 
  
        chomp($line); # you can avoid this you are already chomping the var before sending to subroutine 
        $parent = (split /,/,$line)[8];
        print "$parent\n";
        $len = length($parent);
        print "$len\n";
        # if ( $parent )  will be sufficient to check if its empty or not no need to check its length.
        if ($len == 0) {
                print "Please goto foreach\n";
                return 1;
        }
        else{
                while(<OUT>) {
                        chomp;
                        my $field = (split/,/)[6];
                        # if $field & $parent are string then user "eq" for comparison 
                        if ($field == $parent){
                                my $line = $_;
                                print "ok\n";
                                #print "$parent|$field|$line\n";
                                sleep(2);
                                Lookup($line,*MASTER,$outputfile); # once code is here then this will be infinite loop :) 
                        }
                }
         }
}