Mini Shell

#! /usr/bin/python2.7

# 2)  Sorting Test
#
#     Sort an input file that consists of lines like this
#
#         var1=23 other=14 ditto=23 fred=2
#
#     such that each output line is sorted WRT to the number.  Order
#     of output lines does not change.  Resolve collisions using the
#     variable name.   e.g.
#
#         fred=2 other=14 ditto=23 var1=23
#
#     Lines may be up to several kilobytes in length and contain
#     zillions of variables.

# This implementation:
# - Reads stdin, writes stdout
# - Uses any amount of whitespace to separate fields
# - Allows signed numbers
# - Treats illegally formatted fields as field=0
# - Outputs the sorted fields with exactly one space between them
# - Handles blank input lines correctly

import re
import sys

def main():
    prog = re.compile('^(.*)=([-+]?[0-9]+)')
    def makekey(item, prog=prog):
        match = prog.match(item)
        if match:
            var, num = match.groups()
            return int(num), var
        else:
            # Bad input -- pretend it's a var with value 0
            return 0, item
    for line in sys.stdin:
        items = sorted(makekey(item) for item in line.split())
        for num, var in items:
            print "%s=%s" % (var, num),
        print

main()