Actually I have to run the above code recursively to get the result: So here is my complete code:

#!/usr/bin/perl -w
use diagnostics;
use warnings;

open $fh, "<", "$ARGV[0]" or die "Could not open $ARGV[0]: $!";
sub getsub{
        my $sub = $_[0];
        print "inside sub for $sub\n";
        seek $fh, 0, 0;
        while  (<$fh>) {
        if (/\.subckt $sub/../\.ends/)  {
                print "starting from $_\n";
                if (/^x/) {
                        $line = $_;
                        while (($nxt = readline($fh)) =~ /^\+/) {
                                $line = $nxt;
#                               print "line changed to $line\n";
                        }
                        $line =~ s/\s+$//;
#                       print  "last line is $line\n";
                        my $sub = (split '\s', $line)[-1];
                        print "subcircuit found is $sub in $line\n";
            my $pos = tell($fh);
                        print "position in file set to $pos\n";
                        getsub ($sub);
                        seek $fh, $pos, 0;
                        $pos = tell ($fh);
                        print "position in file restored to $pos\n";
            print "line is now $_";
                }
        }
        }
}

while  (<$fh>) {
        if ($_ =~ /^xa1/) {
                $line = $_;
                print "line found to be $line\n";
                while (($nxt = readline($fh)) =~ /^\+/) {
                        $line = $nxt;
                        #print "line changed to $line\n";
                }
        $line =~ s/\s+$//;
#       print  "last line is $line\n";
        my $sub = (split '\s', $line)[-1];
        print "subcircuit found is $sub in $line\n";
        getsub($sub);
        }
}
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The file on which I am running the code is too big to be shared. The problem I am getting is inside the subroutine. What I want is whenever I return from the recursive call from the subroutine I want to start from the position where I left off in that routine. So I saved the position in $pos and used that in seek after the recursive call as suggested by you. When I return back from a recursive call I tried to check the line which I am on using the print statement at the end of the subroutine. But it shows $_ to be blank. Also, the if block starts from the beginning again creating an infinite loop. Why is this happening?

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