I am not a fan of the emacs default behaviour of storing backup
files in the same directory as the original file, suffixed with a
~. mg, being a lightweight emacs, does the same, but this
behaviour can be changed with the command
backup-to-home-directory, which puts the backup files in
${HOME}/.mg.d.
I created the mg rc file, .mg with the contents:
backup-to-home-directory global-set-key "\^cg" goto-line
However, this did not change the behaviour of mg. Backups were
still being placed in the directory containing the edited file. I
suspected this might be some side-effect of running inside WSL, so I
needed the source code of mg to investigate. This can be
obtained via the Debian
packages repository.
The culprit turned out to be the function expandtilde,
which uses getlogin to obtain
the user name. However, under WSL, the function returned NULL. My
guess this is because the controlling terminal is invoked by the
preferred terminal emulator, wsltty, or its helper
wslbridge. I followed the advice on the getlogin
man page and used getenv to grab the value of
LOGNAME>. The following unified diff shows the patch:
--- fileio_orig.c 2018-03-30 12:00:37.169010300 +0100
+++ fileio.c 2018-03-30 12:03:56.435206400 +0100
@@ -726,7 +726,7 @@
return(ret);
}
if (ulen == 0) { /* ~/ or ~ */
- if ((un = getlogin()) != NULL)
+ if ((un = getenv("LOGNAME")) != NULL)
(void)strlcpy(user, un, sizeof(user));
else
user[0] = '\0';
Note that mg obtains the user's home directory from
/etc/passwd, so home/mark is the location for
.mg.d, rather than using my faked setting of ${HOME} (see
previous journal entry).
