import os

def wrap(f):
    """
    Wraps a function so that if it's entered *by itself*
    in the interpreter without ()'s, it gets called anyway
    """
    class W:
        def __init__(self, f):
            self.f = f
        def __repr__(self):
            x =apply(self.f)
            if x:
                return repr(x)
            else:
                return ''
    return W(f)

def ls():
    """
    Produces a directory listing of the current directory.    
    Usage:   ls
    """
    os.system('ls -Fs')
    return None

ls = wrap(ls)

def lsd(directory):
    """
    Produces a directory listing of the given directory.    
    Usage:   lsd(directory)
    """
    os.system('ls -Fs '+directory)
    return None

def ll():
    """
    Produces a "ls -ltr" directory listing of the current directory.    
    Usage:   ll
    """
    os.system('ls -ltr')
    return None

ll = wrap(ll)


def pwd():
    """
    Changes the working python directory for the interpreter.    
    Usage:   pwd       (no parens needed)
    """
    return os.getcwd()

pwd = wrap(pwd)


def cd (directory):
    """
    Changes the working python directory for the interpreter.
    
    Usage:   cd(directory)      where 'directory' is a string
    """
    os.chdir(directory)
    return

def cat(file):
    """
    call the unix cat command with file as the argument
    Usage:  cat(filename)
    """
    os.system('cat '+file)
    return None

def emacs(file=""):
    """
    open file in Emacs
    """
    os.system("emacs -nw " + file)
    return None

def less(file):
    os.system("less "+file)
    return None

def rm(file):
    os.system("rm "+file)
    return None

def rmdir(directory):
    os.system("rm -rf " + directory)
    return None

def gv(file):
    os.system("gv "+file)
    return None

def acroread(file):
    os.system("acroread "+file)
    return None

def eog(file):
    os.system("eog "+file)
    return None