I recently worked on a migration from OpenVMS to Red Hat Linux, and spent some serious effort porting VMS DCL (Direct Command Line) scripts to Python and Bash. The long-time VMS people were completely unfamiliar with the Linux command line, so we went looking for some good online resources that mapped DCL to Bash. (See my Python course on this site for our training in that language.)
The University of Hamburg offers a very clean and succinct document, “OpenVMS Commands with unix equivalents”, at https://www3.physnet.uni-hamburg.de/physnet/vms-unix-commands.html . It discusses not just commands but also operators and branching statements (if, while, etc.).
The Jodrell Bank Centre for Astrophysics hosts the page “Everything you ever wanted to know about VMS and were afraid to ask”, which has a good discussion of files and folders, some commands and special characters. See http://www.jb.man.ac.uk/~multi/mbvms.html .
Fermilab (yes, that Fermilab) covers commands, files, editing and authentication on the page “Unix for VMS Users”. Find it at https://www-bd.fnal.gov/controls/linux/vms2unix.html .
The Australia Telescope National Facility hosts “Some Useful Linux/UNIX (and VMS) Commands” with one of the longer lists of commands, at http://www.narrabri.atnf.csiro.au/observing/users_guide/html_old_20090512/Some_Useful_Linux_UNIX_and_.html .
If you’ve got more resources, please let me know through the Contact page on this site. Thanks!