[wp-hackers] re:re: GPL

Michael Torbert mrtorbert at gmail.com
Sun Dec 14 19:26:42 GMT 2008


The GNU GPL license is very specific on plugins.  I'll include the text so
that there's no misunderstanding here.

*If a program released under the GPL uses plug-ins, what are the
requirements for the licenses of a plug-in?It depends on how the program
invokes its plug-ins. If the program uses fork and exec to invoke plug-ins,
then the plug-ins are separate programs, so the license for the main program
makes no requirements for them.If the program dynamically links plug-ins,
and they make function calls to each other and share data structures, we
believe they form a single program, which must be treated as an extension of
both the main program and the plug-ins. This means the plug-ins must be
released under the GPL or a GPL-compatible free software license, and that
the terms of the GPL must be followed when those plug-ins are distributed.If
the program dynamically links plug-ins, but the communication between them
is limited to invoking the 'main' function of the plug-in with some options
and waiting for it to return, that is a borderline case.*

I said nothing about the output of a program (which is also covered in the
text of the license, but that doesn't apply to this discussion).  Code
written in PHP doesn't apply.  PHP isn't under the GNU GPL license anymore,
for the very reason of the contradictions in writing code with it.  Same
with Apache.  (Neither WordPress nor its plugins require Apache to run
anyway.)  Remember, Open Source != GNU GPL.  There are many open source
licenses available, this is just one of them.


This is not correct. The GPL is all about distribution and simply using GPL
software does not mean that anything you develop to work with it must be
GPL. The output of GPL'd code is not covered by the license, only the source
code itself is. So, if you use WordPress source code in a plugin or theme
then the plugin or theme must be GPL version 2, the same as WordPress.
However, simply combining PHP code with a WordPress function call may not
necessarily mean that a theme or plugin must be GPL. There are two opposing
schools of thought on that issue and neither is wrong - there simply is no
case law to establish whether using a function creates a derivative work.

Then, to make matters more complicated, the GNU/GPL recognises "fair use".
Some themes comprise templates that are made up of hundreds of lines of HTML
and custom PHP, with only a few lines for the loop, for example, and these
may fall under fair use laws. Fair use does not require that the work is
licensed GPL.

If you use your argument that software that is dependent on parent software
to run must inherit the license of the parent then every webpage would be
under the Apache (or other server software) license and all PHP code would
be using the PHP license. This simply does not hold true.

You also do not have to agree to anything when you simply use GPL code. The
license imposes obligations when you modify and/or distribute the code but
agreement is not part of the GPL. Of course, you only have the right to use
the GPL'd code under the terms of the license.

Theres more information in the GPL FAQ here if you are interested:


> > You are mistaken.  Windows isn't under the GNU GPL.  If you write
> the is dependent on parent software to run (ie a WordPress plugin or
> and that parent software is GPL, then the child software must inherit the
> GPL license.  You agree by these terms when you use the parent software.


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