Perl - 以相反顺序逐行读取文件

Question

这个问题已经有答案了:

已关闭 13 年前。

Possible Duplicate:
How can I read lines from the end of file in Perl?

首先读取最后一行，然后读取最后一行，依此类推。文件太大，无法装入内存。

Answer 1

以相反的顺序读取行:

use File::ReadBackwards;

my $back = File::ReadBackwards->new(shift @ARGV) or die $!;
print while defined( $_ = $back->readline );

我最初误读了这个问题，以为你想以交替的方式向后和向前阅读——这似乎更有趣。 :)

use strict;
use warnings;
use File::ReadBackwards ;

sub read_forward_and_backward {
    # Takes a file name and a true/false value.
    # If true, the first line returned will be from end of file.
    my ($file_name, $read_from_tail) = @_;

    # Get our file handles.
    my $back = File::ReadBackwards->new($file_name) or die $!;
    open my $forw, '<', $file_name or die $!;

    # Return an iterator.
    my $line;    
    return sub {
        return if $back->tell <= tell($forw);
        $line = $read_from_tail ? $back->readline : <$forw>;
        $read_from_tail = not $read_from_tail;
        return $line;
    }

}

# Usage.    
my $iter = read_forward_and_backward(@ARGV);
print while defined( $_ = $iter->() );