Re: EPNG Chunk Registration

> Example
>
> The exEc chunk containing #/usr/bin/env xdg-open should open the image
> in the default image viewer, given a system with xdg-open and GNU
> coreutils installed.

This looks like a reference to the UNIX '#!' hack; in UNIX the kernel
looks at the first few bytes of an executable and, if they start with
'#!' it executes the file in the following (space delimited) bytes.
It is a big, horrible, security nightmare.  I can't imagine anyone in
their right mind would actually implement such a facility for a PNG.

Perhaps more important, I wouldn't want to encourage anyone,
regardless of mindset, to do so.  Glenn's sarcastic comment on the
original link might help if you don't understand the history of the
'#!' mess, or the consequences of executing arbitrary data.

To understand the example you may need to know that '/usr/bin/env' is
a shorthand for 'sh -c', which, in its turn, is  longhand for the
empty string; in other words it means 'execute whatever follows'.

The example as stated is just a restatement of the original (or more
likely Xerox PARC) Apple meme of associating a document (a PNG is a
document) with an 'editor'; a preferred application to use for a
default action ('open') on the document.  Since PNG is such a generic
format there may be some merit in what I hope underlies the proposal.

John Bowler <[email protected]>

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