This is the source code
of the UNMSG utility. The sources are based on Joe Meadows' UNMESSAGE
utility, available from the VMS freeware CDs.
Nonexecutable message files, for example SYS$MESSAGE:SYSMSG.EXE, have the message section always at VBN 2, no matter which platform the message file was produced for, VAX, Alpha or I64. So the original source code was simplified to decompile the messages from the hard coded VBN to make it work on all platforms.
Please note, there is no check whether the passed-in file is indeed a nonexecutable message file. That wasn't the case in the orignal tool and it is known that VMS code doesn't do this either.