The nmh Message Handling System is a set of command line tools for reading your mail from within the shell on a Posix compatible system such as Linux. It has support for an unseen sequence to enable automatic tracking of which messages have been read. Unfortunately the rcvstore command does not lock the .mh_sequences file which means it is possible to corrupt it. Most other MDAs won't update the unseen sequence even if they otherwise support MH folders.

An alternative to the unseen sequence would be to use a read sequence. Unlike an unread sequence this does not need to be updated when delivering mail only when viewing it which is done synchronously. To implement this I wrote a short shell script to use as a wrapper for the showproc and showmimeproc.

[ $# -ge 3 ] || exit 1
mark cur -sequence "$1" -add -nozero
shift 2
[ "${CMD}" = "-" ] && CMD=/usr/lib/mh/mhl
exec "${CMD}" "$@"

This can then be invoked via your .mh_profile with lines like the following:

sequence-negation: un
showproc: /home/wish/bin/readseq read -
showmimeproc: /home/wish/bin/readseq read /usr/bin/mh/mhshow 

The use of a hyphen to force invocation of the mhl command is to bypass special treatment of showprocs called mhl by the show program. The sequence-negation entry allows the read sequence to be used as a mechanism to list or display unread messages.

One down side of using a read sequence rather than an unseen sequence is that new and related commands don't work with negated sequences.