Pash-Project/Pash — pull request #127 by Ventero (2013-05-29 21:12:43+00:00)
Title:  Allow single-character parameter prefixes. 

The grammar for parameter names explicitly requires at least two characters (one in first_parameter_char_pattern and at least one in parameter_chars). However, Powershell allows single character names, which probably means this is a bug in the spec.