import re

backslash_shell_quote_re = re.compile(r'([^A-Za-z0-9_.,:/])')
def shell_escape(s, flavor='sh'):
    """
    Escape a random string (s) so that it reads as a single word when
    undergoing shell command-line parsing.

    The default flavor should be safe for all mainstream shells I know
    about, but there are some other escaping modes which may result in
    more compact or more readable output.

    Available flavors:
       bash, zsh: use dollar-quoting ($'foo')
       sh, csh: use standard single-quotes except when quoting single-
               quote characters
       backslash: use no quotes; escape all unsafe characters with a
               backslash

    """

    if flavor in ('bash', 'zsh'):
        return "$'%s'" % s.replace('\\', '\\\\').replace("'", "\\'")
    elif flavor in ('sh', 'csh'):
        return "'%s'" % s.replace("'", "'\"'\"'")
    elif flavor == 'backslash':
        return backslash_shell_quote_re.sub(r'\\\1', s)
    else:
        raise ValueError("Unknown shell quoting flavor %s" % flavor)