As the Section Settings from the Environment explains, some MH commands add environment variables that are passed to environments of their child processes. MH commands also read their own environments, set by their parent processes. For example, if the variable MHCONTEXT is set, MH commands will use that pathname for the MH context file instead of the file named context in the MH directory.
The Table below was adapted from the mh-profile(5) manual page. For more description of each environment variable, see that manual page. This table doesn't include environment variables used by parts of MH (like BBoards) which this book doesn't cover.
Table: Environment Variables that MH Checks
NOTE: xmh Release 4, and possibly earlier versions too, ignore the MH environment variable at startup time. It always reads the .mh_profile in your home directory to find the Path: of your MH directory. There's a workaround in Section Conflicts Between xmh and MH Customization.
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This file is from the third edition of the book MH & xmh: Email for Users & Programmers, ISBN 1-56592-093-7, by Jerry Peek. Copyright © 1991, 1992, 1995 by O'Reilly & Associates, Inc. This file is freely-available; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation. For more information, see the file copying.htm.
Suggestions are welcome: Jerry Peek <jpeek@jpeek.com>