Re^5: about link()

I suspect that whatever you are using to "edit" the jpg, isn't editing it in-place, but rather when you save the changes you made, it deletes the original file and then write a new one with the original name and the new contents. This (by design) breaks the link.

For reference and an authoritative description, see this forum post by the guy that implemented link on win32.

To prove it is the editor rather than perl that is at fault, try this sequence of steps:

c:\test\junk>dir
18/02/2012  22:09               633 a.jpg

c:\test\junk>perl -E"say link 'a.jpg', 'b.jpg';"
1

c:\test\junk>dir
18/02/2012  22:09               633 a.jpg
18/02/2012  22:09               633 b.jpg

c:\test\junk>md5sum a.jpg
56c800418e498e40ae9bc4c1e4023341 *a.jpg

c:\test\junk>md5sum b.jpg
56c800418e498e40ae9bc4c1e4023341 *b.jpg

c:\test\junk>perl -E"open I,'+<:raw','a.jpg';seek I,400,0;syswrite I,0
+xffffffff,4;close I"

c:\test\junk>md5sum a.jpg
8bc46c67f8e5d8c0caf4c7c59db66779 *a.jpg

c:\test\junk>md5sum b.jpg
8bc46c67f8e5d8c0caf4c7c59db66779 *b.jpg
[download]

Of course, the jpgs aren't valid any more after the edit above, but it should convince you that editing one also edits the other.

With the rise and rise of 'Social' network sites: 'Computers are making people easier to use everyday'

Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.

"Science is about questioning the status quo. Questioning authority".

In the absence of evidence, opinion is indistinguishable from prejudice.

The start of some sanity?

Comment on Re^5: about link() Download Code

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Re^6: about link() by exilepanda (Friar) on Feb 19, 2012 at 04:22 UTC
Thank you very much! This explains everything. So I tried with this code : `open O, ">a.bin"; binmode O; print O "Hello World!"; close O; link "a.bin", "b.bin"; open L, ">b.bin"; binmode L; print L "Bye World!"; close L; open O, "a.bin"; print while ( <O> ); close O; # prints "Bye World!"` [download] This proved an in-place edit works in binary files as expected. It's glad to know that it's my fault!! Otherwise I don't know how to fix it. Good day! =)	[reply] [d/l]

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Re^6: about link()
by exilepanda (Friar) on Feb 19, 2012 at 04:22 UTC

open O, ">a.bin";
binmode O;
print O "Hello World!";
close O;

link "a.bin", "b.bin";

open L, ">b.bin";
binmode L;
print L "Bye World!";
close L;

open O, "a.bin";
print while ( <O> );
close O;

# prints "Bye World!"
[download]

[reply]
[d/l]