open: allow overriding default program

Instead of xdg-open (or open on MacOS), allow forcing a program to open
a message part. The program is determined in that order of priority:

1) If :open has arguments, they will be used as command to open the
   attachment. If the arguments contain the {} placeholder, the
   temporary file will be substituted, otherwise the file path is added
   at the end of the arguments.

2) If a command is specified in the [openers] section of aerc.conf for
   the part MIME type, then it is used with the same rules of {}
   substitution.

3) Finally, fallback to xdg-open/open with the file path as argument.

Update the docs and default config accordingly with examples.

Fixes: https://todo.sr.ht/~rjarry/aerc/64
Co-authored-by: Jason Stewart <support@eggplantsd.com>
Signed-off-by: Robin Jarry <robin@jarry.cc>
Tested-by: Tim Culverhouse <tim@timculverhouse.com>
Acked-by: Moritz Poldrack <moritz@poldrack.dev>

1 files changed, 19 insertions, 0 deletions

diff --git a/doc/aerc-config.5.scd b/doc/aerc-config.5.scd
index d6b56fa0..8b7aa55c 100644
--- a/doc/aerc-config.5.scd
+++ b/doc/aerc-config.5.scd
@@ -508,6 +508,25 @@ that aerc does not have alone.
 Note that said email body is converted into UTF-8 before being passed to
 filters.
 
+## OPENERS
+
+Openers allow you to specify the command to use for the *:open* action on a
+per-MIME-type basis. They are configured in the *[openers]* section of
+aerc.conf.
+
+*{}* is expanded as the temporary filename to be opened. If it is not
+encountered in the command, the temporary filename will be appened to the end
+of the command. Environment variables are also expanded. Tilde is not expanded.
+
+Example:
+
+```
+[openers]
+text/html=surf -dfgms
+text/plain=gvim {} +125
+message/rfc822=thunderbird
+```
+
 ## TRIGGERS
 
 Triggers specify commands to execute when certain events occur.