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#!/usr/bin/perl -w # # Proof-of-concept for using minimal memory to search huge # files, using a sliding window, matching within the window, # and using on /gc and pos() to restart the search at the # correct spot whenever we slide the window. # # Doesn't correctly handle potential matches that overlap; # the first fragment that matches wins. # use strict; use constant BLOCKSIZE => (8 * 1024); &search("bighuge.log", sub { print $_[0], "\n" }, "<img[^>]*>"); sub search { my ($file, $callback, @fragments) = @_; local *F; open(F, "<", $file) or die "$file: $!"; binmode(F); # prime the window with two blocks (if possible) my $nbytes = read(F, my $window, 2 * BLOCKSIZE); my $re = "(" . join("|", @fragments) . ")"; while ( $nbytes > 0 ) { # match as many times as we can within the # window, remembering the position of the # final match (if any). while ( $window =~ m/$re/oigcs ) { &$callback($1); } my $pos = pos($window); # grab the next block $nbytes = read(F, my $block, BLOCKSIZE); last if $nbytes == 0; # slide the window by discarding the initial # block and appending the next. then reset # the starting position for matching. substr($window, 0, BLOCKSIZE) = ''; $window .= $block; $pos -= BLOCKSIZE; pos($window) = $pos > 0 ? $pos : 0; } close(F); }

In reply to Matching in huge files by dws

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