note
tybalt89
<p>
XY problem?
<br><br>
Looking at your code it appears you are reading kernel logs for temperature problems, but only after a certain unix time.
<br>
It may be possible to use Search::Dict to find the first line in the file on or after a specified time and then read forward to the end.
<br>
No backward reading would be required.
<br><br>
It would look something like this:
</p>
<code>
#!/usr/bin/perl
use strict; # https://perlmonks.org/?node_id=11126426
use warnings;
use Search::Dict;
use Date::Parse qw( str2time );
use Time::HiRes qw( time );
my $day = 60 * 60 * 24;
# commented code used to create 209M file;
#my $str = join '', map { localtime( time + $_ * $day) .
# " kernel: log entry\n" } -5e6 .. 5;
#print $str;
#use Path::Tiny; path('d.searchdict')->spew($str);
#print "string length = @{[length $str]}\n";
my $want = time - 1.1 * $day;
my $start = time;
open my $fh, '<', 'd.searchdict' or die;
look $fh, $want, {
comp => sub { $_[0] <=> $_[1] },
xfrm => sub { str2time substr shift, 0, 24 },
};
printf "look took %.3f seconds\n", time - $start;
while( <$fh> ) # now read to end of file
{
print;
}
</code>
<p>
On the other hand, maybe a real read backwards would work better,
so here's a simple package I threw together:
</p>
<code>
#!/usr/bin/perl
use strict; # https://perlmonks.org/?node_id=11126426
use warnings;
my $str = join '', map '.' x $_ . "this is line $_\n", 1 .. 60;
print $str;
print "string length = ", length $str, "\n";
my $backwards = Tybalt89BackwardsHeReads->new( \$str ) or die;
while( defined( $_ = $backwards->line ) )
{
print;
}
package Tybalt89BackwardsHeReads; #######################################
sub line
{
my ($self) = @_;
if( @{ $self->{lines} } == 0 and $self->{where} )
{
my $window = 1024; # window size, adjust to suit
my $pos = $self->{where} - $window;
$pos < 0 and $pos = 0;
seek $self->{fh}, $pos, 0;
read $self->{fh}, my $data, $self->{where} - $pos;
$pos and $data =~ s/^.*\n// ? ($pos += $+[0]) : die "increase window size";
$self->{lines} = [ split /^/, $data ];
$self->{where} = $pos;
}
return pop @{ $self->{lines} };
}
sub new
{
my ($self, $filename) = @_;
open my $fh, '<', $filename or die "$! on $filename";
bless { fh => $fh,
where => ref $filename ? length $$filename : -s $filename,
lines => [] }, ref $self || $self;
}
1; # so if split off, package ends with true
</code>
<p>
Use your real filename in the ->new() call instead of the string reference I was using for testing.
And you can remove the string generation code also.
<br><br>
You may want to change the package name :)
<br><br>
P.S. I enjoyed writing the read backwards code, thanks for the inspiration!
</p>
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