How to pull out part of "ParserComment" and add to custom field

I have a Parser Comment coming in from XLF:

"TOURID-web-shell&CONTEXT-development preview guard hash top text"

I would like to pull out "web-shell" and put into a custom field. I have a macro displaying the parser comment just fine, but when I try to do any string processing it doesn't work. 

Do you have example of using a string processing on this field?

Thanks,

Tim

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