Can I call any other executable/program from wireshark?

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Thank you for asking for this clarification. If there are financial implications to your question you should consult a lawyer for your jurisdiction and not rely on random postings on the Internet.

Wireshark is distributed under the GNU GPLv2 or later, see here for the license details.

Most parts of Wireshark are covered by a "GPL version 2 or later" license. Some files are covered by different licenses that are compatible with the GPLv2.

If you don't distribute your modified version then there is no problem at all.

If you wish to distribute your modified version, then you will have to make your changes to Wireshark available to the recipients of your modified version.

Note: The subsequent is somewhat informed comment on my part.

If your associated program can be run standalone, i.e. does not depend on Wireshark for it's functionality, and your changes to Wireshark still allow it to run without the associated executable then I don't think your associated program must be GPLv2 compatible. See the GPLv2 FAQ items on "Combining work with code released under the GPL", and in particular programs and plugins and Aggregation.