@EXEC[command] : Execute command and return its numeric exit code.
Command can be an alias, internal command, external command, .BTM, .BAT, or .CMD file.
By default, @EXEC returns the result code from command (see the ? and _? variables). However, if in command you preface the command name with @ then @EXEC returns an empty string.
Example:
PROMPT=%@exec[@color 15 on %@if[%@removable[%_disk] eq 0,2,4] & echos [%_cwd%] & color 11 on 0]$s
See also: @EXECSTR.