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

=head1 DESCRIPTION

Removes duplicate lines from bash history file.
The contents are first saved to ~/.bash_history_old.

Needed to keep file size trimmed, to prevent deletion of contents.
Deletion occurs when a line count limit is reached (a bash config item I think,
and mine is currently set at 5000 lines).

=cut


   # Read history file.
   # - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
    my $history_file = $ENV{HOME} . '/.bash_history';
  # my $history_file = '/tmp/.bash_history';
    my @line;
    open FILE, '<' . $history_file or die "$history_file: $!";
    {
        @line = <FILE>;
        close FILE;
    }

   # Save contents.
   # - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
    my $history_file_old = $history_file . '_old';
    umask 0077; # fully private, no permissions to group or others
    open FILE, '>' . $history_file_old or die "$history_file_old: $!";
    {
        for( @line )
        {
            print FILE;
        }
        close FILE;
    }

   # Map lines and remove duplicates.
   # - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
    my @line_collapsed;
    my %line;
    for( ;; )
    {
        my $line = pop @line;
        $line or last;

        $line{$line} and next;

        unshift @line_collapsed, $line;
        $line{$line} = 1;
    }

   # Save collapsed history.
   # - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
    open FILE, '>' . $history_file or die "$history_file: $!";
    {
        for( @line_collapsed )
        {
            print FILE;
        }
        close FILE;
    }