G'day babysFirstPerl,

Welcome to the Monastery.

I'd use the following steps:

  1. Open the file once.
  2. Read through all the headers and capture the file position (tell).
  3. Read the remaining lines and calculate the last data line (based on total lines in file and known number of footer lines).
  4. Reposition the file pointer to the start of the data (seek) and reset the line counter ($.).
  5. Read just the data lines and process as required.
  6. Close the file once.

Here's my test code (pm_1139175_skip_head_and_foot.pl): 

#!/usr/bin/env perl

use strict;
use warnings;
use autodie;

my $file = 'pm_1139175_skip_head_and_foot.txt';
my ($headers, $footers) = (2, 3);

open my $fh, '<', $file;

<$fh> for 1 .. $headers;
my $last_head_pos = tell $fh;

1 while <$fh>;
my $last_data_line = $. - $footers;

seek $fh, $last_head_pos, 0;
$. = $headers;

while (<$fh>) {
    last if $. > $last_data_line;
    print;
}

close $fh;

[download]

Given this input:

$ cat pm_1139175_skip_head_and_foot.txt
head1
head2
data1
data2
data3
data4
foot1
foot2
foot3

[download]

That script produces:

$ pm_1139175_skip_head_and_foot.pl
data1
data2
data3
data4

[download]

— Ken

In reply to Re: More efficient way to exclude footers by kcott
in thread More efficient way to exclude footers by babysFirstPerl

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