I am mostly writing this for my own reference.
Because of the Sketch mask trick, when trying to export icons they had a mask in them that I did not want. Basically I had to remove all masks across 75 icons. Since SVGs are just text files, you can do some regex processing to find all <mask> elements:
(?m)\<mask(.*)\/mask\>
The (?m) part is a filter that makes the regex work across multiple lines.
Sources