Re: [MacPerl] Processing file backwards?

[Mark Manning/Simulacron I <markem@flash.net>]

There is a fairly easy way to do this.  I read about it in some book
years ago.  It goes like this:

1. First read through the file.  As you go, note how many characters
you've read in per line.

2. Store the locations of the beginning of each line in an array.  Like
so:

	[0][0] = 0;	#	Starting location.
	[0][1] = 52;	#	Length of line #1.
	[1][0] = 53;	#	Start of line #2
	[1][1] = 5;	#	Length of line #2.
	etc....

3. You should now have a list going from zero to X.  Reverse this list.

4. Open the file as if it were a random access file.  Start moving to
each of the locations you previously found and reading the lines in.

Example:

	@fileInfo = ();
	$fileInfo[++$#fileInfo][0] = 0;
	open( THEFILE, "myFile.dat" ) || die $!;
	while( <THEFILE> ){
		$fileInfo[$#fileInfo][1] = length();
		$fileInfo[++$#fileInfo][0] =$fileInfo[$#fileInfo-1][0]+
			$fileInfo[$#fileInfo-1][1];
		}

	close( THEFILE );
	@newInfo = reverse @fileInfo;
	undef @fileInfo;

	sysopen( THEFILE, "myFile.dat" ) || die $!;
	while( $#newInfo > -1 ){
		sysseek( THEFILE, $newInfo[$#newInfo][0], 0 );
		sysread( THEFILE, $theLine, $newInfo[$#newInfo][1] )
#
#	Do whatever
#
		}

	close( THEFILE );
	exit( 0 );

I'm doing this off the top of my head but the idea should work fine.

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