Add a command-error hook when a command fails, from Hugh Davenport in

GitHub issue 3973.

tmux.1

@@ -4889,6 +4889,14 @@ layout after every
 set-hook -g after-split-window "selectl even-vertical"
 .Ed
 .Pp
+If a command fails, the
+.Ql command-error
+hook will be fired.
+For example, this could be used to write to a log file:
+.Bd -literal -offset indent
+set-hook -g command-error "run-shell \\"echo 'a tmux command failed' >>/tmp/log\\""
+.Ed
+.Pp
 All the notifications listed in the
 .Sx CONTROL MODE
 section are hooks (without any arguments), except
@@ -4921,6 +4929,8 @@ Run when focus exits a client
 Run when a client is resized.
 .It client-session-changed
 Run when a client's attached session is changed.
+.It command-error
+Run when a command fails.
 .It pane-died
 Run when the program running in a pane exits, but
 .Ic remain-on-exit