Re^15: Question about binary file I/O

[TheMartianGeek]

Actually, that's a good idea. The problem with that, though, is that the print function completely erases the rest of the file. Now that I think about it, I don't know if I ever found a good way to overwrite characters in a file without erasing the rest of the file...

[BrowserUk]

The problem with that, though, is that the print function completely erases the rest of the file.

It won't if you use the right open mode; ie. '+<':

#! perl -sw
use strict;

## Open for reading and writing
open IO, '+<', 'junk.dat' or die $!;

seek IO, 11, 0;
print IO 'this overwrites';

close IO;

__END__

C:\test>type junk.dat
xxxxxxxxx
xxxxxxxxx
xxxxxxxxx
xxxxxxxxx

C:\test>junk59

C:\test>type junk.dat
xxxxxxxxx
this overwritesxxxxx
xxxxxxxxx

[TheMartianGeek]

Oh, I see. That's useful.

Okay, my next question is kind of hard to describe...basically, I want to find all blocks of data in a file that are composed of a single specified character and have a specified minimum length. (Say, all blocks of character 0x20 that are at least 12 bytes long.) BUT, said blocks a) shouldn't cross certain boundaries (say, they shouldn't overlap between groups of 1000 bytes) and b) shouldn't be taken into account if they are part of a reserved block marked with a certain keyword (say, the ASCII characters "U S E D" followed by the block length). I don't really even know where to start on this...

[BrowserUk]

I don't really even know where to start on this...

A new SoPW. And a much clearer description of

1. The contents of the file and its formatting.

   With preferably an example of the data that contains typical contents and at least 3 records that match. If that means it would be too big to post here, then making an example available off-site shouldn't be too hard.

2. What you are actually searching for.

   Ie. less "(Say, all blocks of character 0x20 that are at least 12 bytes long)" & "say, they shouldn't overlap between groups of 1000 byte" & "(say, the ASCII characters "U S E D" followed by the block length)".

3. And what you want to do once you've found them.