status docs: add current-command

Note deprecation of $_.

[ci skip]

doc_src/index.hdr.in

@@ -677,7 +677,7 @@ set index 2
 set letters a b c d
 echo $letters[$index] # returns 'b'
 \endfish
-However using variables as indices for command substitution is currently not supported, so 
+However using variables as indices for command substitution is currently not supported, so
 \fish
 echo (seq 5)[$index] # This won't work
 
@@ -923,7 +923,7 @@ The user can change the settings of `fish` by changing the values of certain var
 
 `fish` also sends additional information to the user through the values of certain environment variables. The user cannot change the values of most of these variables.
 
-- `_`, the name of the currently running command.
+- `_`, the name of the currently running command (though this is deprecated, and the use of `status current-command` is preferred).
 
 - `argv`, an array of arguments to the shell or function. `argv` is only defined when inside a function call, or if fish was invoked with a list of arguments, like `fish myscript.fish foo bar`. This variable can be changed by the user.
 

doc_src/status.txt

@@ -11,6 +11,7 @@ status is-command-substitution
 status is-no-job-control
 status is-full-job-control
 status is-interactive-job-control
+status current-command
 status filename
 status fish-path
 status function
@@ -43,6 +44,8 @@ The following operations (sub-commands) are available:
 
 - `is-no-job-control` returns 0 if no job control is enabled. Also `--is-no-job-control` (no short flag).
 
+- `current-command` prints the name of the currently-running function or command, like the deprecated `_` variable.
+
 - `filename` prints the filename of the currently running script. Also `current-filename`, `-f` or `--current-filename`.
 
 - `fish-path` prints the absolute path to the currently executing instance of fish.