#!/usr/bin/perl
use strict;
use warnings;

my $infile = 'infile.txt';
open my $fh,'<',$infile
     or die "Could not open $infile : $!";

my $lineno = 0;     
while (<$fh>){
  ++$lineno;
  if (/^ node \s+ (\d+) \s+ \w+ : $ /x){
    print "lineno $lineno : $1\n";
  }   
}
close $fh;
print "$lineno lines read from $infile\n";