Can you be bit elaborate on the sample that you have provided.

By "the sample", I presume you mean this one (reformatted for readability)?

perl -e"
    local $/ = '~'; 
    push @{ $h{lines } }, $_ while <>; 
" huge.file
[download]

When you call readline (or use the <> operater as above), Perl determines how much to read from the file, by looking for a character (or sequence of characters), that match the current setting of the special variable $/ (also known as the $INPUT_RECORD_SEPARATOR (you'll have to scroll down aways to find it)). Normally, $/ defaults to being a newline. But...

What the sample above does is set the value of $/ = '~';. That means that readline will stop reading when it encounters a '~' in the input stream.

Ie. Instead of readline reading the whole 37 MB in as a single string; then spliting it into a big list; and then assigning that to the array on mass.

The code above, readlines just up to the first '~' character, pushes it onto the array; then loops (while), back to get the next chunk up to the next '~'.

Put another way. Setting $/ = '~';, has the effect of redefining a line, as a sequence of chars terminated by a '~'.

I hope one of those descriptions helps--ask again if it doesn't--because I know of no other langauge that has a standard library that allows you to do this. So when you first encounter it, it is definitely a bit weird.

Hi BrowserUk,

I understood the role of special variable from your notes. I also tried to implement the same in my code. Please find it below:

sub new
{
    my $class   = shift();
    my $self        = {};
    $self->{fname}  = shift() or $self->{fname} = "STDIN";

    print "Inside new in X12.pm\n";

    # Open File Handle
    if ($self->{fname} ne "STDIN")
    {
        # Check For Empty File
        if (not -s $self->{fname})
        {
            #die "Empty or non-existent input file.\n";
            return 0;
        }
        local *IN;
        print "Before File Open\n";
        open(IN, "< $self->{fname}") or return 0; #die "Can't open $se
+lf->{fname} for input: $!\n";
        print "After File Open\n";
        $self->{file} = *IN;
        $self->{fopen} = 1;
    }
    else
    {
        $self->{file} = *STDIN;
    }

    my $line = "";
    while (not length($line))
    {
        print "inside while loop in X12.pm\n";
        $line = readline($self->{file});
        #die "Unexpected EOF in file $self->{fname}\n" if (not defined
+($line));
        return 0 if (not defined($line));
        $line =~ s/^\s+//;  # Strip leading whitespace
        print "line read from the file in X12.pm\n";
    }

    # Get Header Information and Initalize File Read Buffer
    if ($line !~ /^ISA/)
    {
        $self->{fieldOut}   = "*";
        $self->{segOut}     = "\n";
        $self->{compSep}        = "<";
        $self->{fieldSep}   = "\\*";
        $self->{segSep}     = "\\\n";
        print "self in if cond in X12.pm\n";
    }
    elsif (length($line) < 106)
    {
        return 0;
        #die "ISA segment invalid, aborting.\n";
    }
    else
    {
        $self->{fieldOut}   = substr($line, 3, 1);
        $self->{segOut}     = substr($line, 105, 1);
        $self->{compSep}        = substr($line, 104, 1);
        $self->{fieldSep}   = "\\$self->{fieldOut}";
        $self->{segSep}     = "\\$self->{segOut}";
        print "self in else cond in X12.pm\n";
    }

    print "self->{segSep} is $self->{segSep}\n";

    local $/ = $self->{segSep};
#    @{ $self->{lines}} = split(/$self->{segSep}/, $line);
    push @{ $self->{lines}}, $_  while readline($self->{file});
    print "New in X12 complete\n";
    bless($self, $class);
    return $self;
}
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But i dont get the desired results. Am i doing anything wrong? Please let me know.

Thanks,

peacelover1976