The Collaborative International Dictionary of English v.0.48:

Shug \Shug\, v. i. [Cf. Shrug.]
   1. To writhe the body so as to produce friction against one's
      clothes, as do those who have the itch. [Prov. Eng.]
      --Halliwell.
      [1913 Webster]

   2. Hence, to crawl; to sneak. [Obs.]
      [1913 Webster]

            There I 'll shug in and get a noble countenance.
                                                  --Ford.
      [1913 Webster]

The Free On-line Dictionary of Computing (30 December 2018):

SHUG

   Scottish Hypermedia Users' Group