if ($_ =~ /^xa1/) {

##</code><code>##

sub getsub
{
    my $sub = $_[0];
    print "sub entered for $sub\n";
    local $fh;
    seek  $fh, 0, 0;

    while (<$fh>)
    {
        print if /\.subckt $sub/ .. /\.ends/;
    }
}

##</code><code>##

use strict;
use warnings;

open(my $fh, '<', $ARGV[0]) or die "Could not open file: $!";

sub getsub
{
    my $sub = $_[0];
    print "sub entered for $sub\n";

    open my $fh2, '<', 'subs.txt' or die "Could not open file: $!";

    while (<$fh2>)
    {
        print if /\.subckt $sub/ .. /\.ends/;
    }

    close $fh2 or die "Could not close file: $!";
}

while (my $line = <$fh>)
{
    if ($line =~ /^xa1/)
    {
        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"; 
        my $file_pos = tell $fh;
        getsub($sub);
        seek $fh, $file_pos, 0;
    }
}

close $fh or die "Could not close file: $!";

##</code><code>##

 2:55 >perl 1032_SoPW.pl subs.txt
line found to be xa1 a s f a1

last line is xa1 a s f a1
subcircuit found is a1 in xa1 a s f a1
sub entered for a1
.subckt a1 x y z
   xa a b c1
   xb c d e1
   xc f g h1
 .ends

 2:56 >

##</code><code>##

while ((my $nxt = readline($fh)) =~ /^\+/)

##</code><code>##

while (!eof && (my $nxt = readline($fh)) =~ /^\+/)