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I'm attempting to get the last 15 minutes of entries from a httpd access log. I immediately think of a binary search. The problem is, I've never written one. I've attempted to use this code example from the book:Mastering Algorithms with Perl. But it doesn't work for my purpose. Can someone offer help? I'm assuming the best way to search would be based on the date string: perl binary_search_file.pl "Aug 3 07:59:59"
#!/usr/bin/perl -w use strict; use integer; my ( $word, $file ) = @ARGV; open( FILE, $file ) or die "Can't open $file: $!"; my $position = binary_search_file( \*FILE, $word ); if ( defined $position ) { print "$word occurs at position $position +\n" } else { print "$word does not occur in $file.\n" +} sub binary_search_file { my ( $file, $word ) = @_; my ( $high, $low, $mid, $mid2, $line ); $low = 0; # Guaranteed to be the start of a l +ine. $high = ( stat($file) )[7]; # Might not be the start of a line. $word =~ s/\W//g; # Remove punctuation from $word. $word = lc($word); # Convert $word to lower case. while ( $high != $low ) { $mid = ( $high + $low ) / 2; seek( $file, $mid, 0 ) || die "Couldn't seek : $!\n"; # $mid is probably in the middle of a line, so read the rest # and set $mid2 to that new position. $line = <$file>; $mid2 = tell($file); if ( $mid2 < $high ) { # We're not near file's end, so rea +d on. $mid = $mid2; $line = <$file>; } else { # $mid plunked us in the last line, so linear search +. seek( $file, $low, 0 ) || die "Couldn't seek: $!\n"; while ( defined( $line = <$file> ) ) { last if compare( $line, $word ) >= 0; $low = tell($file); } last; } if ( compare( $line, $word ) < 0 ) { $low = $mid } else { $high = $mid } } return if compare( $line, $word ); return $low; } sub compare { # $word1 needs to be lowercased; $word2 doesn't. my ( $word1, $word2 ) = @_; $word1 =~ s/\W//g; $word1 = lc($word1); return $word1 cmp $word2; }

In reply to Using binary search to get the last 15 minutes of httpd access log by mhearse

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