Variable not set properly in perl

[sar123]

I have the following code:

    #!/usr/bin/perl -w
    use warnings;
    use diagnostics;
    
      open $fh , "<", "$ARGV[0]" or die "Could not open file: $!";

      sub getsub{
        my $sub = $_[0];
        print "sub entered for $sub\n";
        while (<$fh>) {
        if (/\.subckt $sub/../\.ends/) {
          print ;
        }
      }
    }

    while  (<$fh>) {
      if ($_ =~ /^xa1/) {
        $line = $_;
        print "line found to be $line\n";
        while ((my $nxt = readline($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);
      }
    }

Here I am trying to print some text between two patterns inside the `getsub` routine. But when I try to run this I enter the subroutine but doesn't enter the if block inside the subroutine. I am trying to run it on the following file:

     .subckt a1 x y z
       xa a b c1
       xb c d e1
       xc f g h1
     .ends

     .subckt c1 x y z
      xa a b f
      xb c d e
      xc f g h
    .ends

    .subckt e1 x y z
      xa a b c1
      xb c d k1
      xc f g h1
    .ends

    xa1 a s f a1

I want to print the contents of the file between ".subckt a1" till ".ends".
I know this could be done by the one liners of perl on the command line, but I want to create some generalized script for different files so I need to go this way only. What is wrong with the above code.