Support busybox ps in process completions

Fixes #6918

share/functions/__fish_complete_pids.fish

@@ -5,6 +5,6 @@ function __fish_complete_pids -d "Print a list of process identifiers along with
 
     # Display the tty if available
     # But not if it's just question marks, meaning no tty
-    ps axc -o pid,ucomm,tty | string match -r -v '^\s*'$fish_pid'\s' | tail -n +2 | string replace -r ' *([0-9]+) +([^ ].*[^ ]|[^ ]) +([^ ]+) *$' '$1\t$2 [$3]' | string replace -r ' *\[\?*\] *$' ''
+    __fish_ps -o pid,comm,tty | string match -r -v '^\s*'$fish_pid'\s' | tail -n +2 | string replace -r ' *([0-9]+) +([^ ].*[^ ]|[^ ]) +([^ ]+) *$' '$1\t$2 [$3]' | string replace -r ' *\[\?*\] *$' ''
 end
 

share/functions/__fish_complete_proc.fish

@@ -1,7 +1,7 @@
-function __fish_complete_proc
+function __fish_complete_proc --inherit-variable ps
     # "comm=" means "print comm field with an empty name", which causes the header to be removed.
     # On many systems, comm is truncated (e.g. on Linux it's 15 chars),
     # but that's okay since commands that accept them as argument also only use those (e.g. pgrep).
     # String removes zombies (ones in parentheses) and padding (macOS adds some apparently).
-    ps -axc -o comm= | string match -rv '\(.*\)' | string trim
+    __fish_ps -o comm= | string match -rv '\(.*\)' | string trim
 end

share/functions/__fish_ps.fish

@@ -0,0 +1,8 @@
+function __fish_ps
+    switch (realpath (command -v ps) | string match -r '[^/]+$')
+        case busybox
+            command ps $argv
+        case '*'
+            command ps axc $argv
+    end
+end