perl special charecter

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　　$_
　　This is a special array for the subroutine duration.U can access it by use $_[<index>]. So the first parmater will be $_[0].
　　The @_ variable is private to the subroutine, @_ is always the parameter list for the current subroutine invocation
　　$PROCESS_ID
　　$$
　　read a file line by line
　　



#!/usr/bin/perl
use strict;
use warnings;
my $dir ="./tmp";
open (FH, "<$dir/txn-history.txt") or die "Couldn't open $dir/txn-history.txt, $!"."\n";
while(<FH>) {
print "$_";
}


　　

perlref
　　If you put a \ in front of a variable, you get a reference to that variable.
　　perlobject
　　perl's subroutine first argument is itself or class/package name.