Generate random string with python. Charset used can be specified via parameters.

random-str.py

#!/usr/bin/env python

import getopt
import sys
import random
import string

DEFAULT_LENGTH = 16

def main():
    try:
        opts, args = getopt.getopt(sys.argv[1:], "huld",
                ['help', 'uppercase', 'lowercase', 'digits'])
    except getopt.GetoptError as err:
        print str(err)
        sys.exit(2)

    selection=''
    for o, a in opts:
        if o in ('-h', '--help'):
            usage()
            sys.exit()
        elif o in ('-u', '--uppercase'):
            selection = selection + string.uppercase
        elif o in ('-l', '--lowercase'):
            selection = selection + string.lowercase
        elif o in ('-d', '--digits'):
            selection = selection + string.digits

    if not selection:
        selection = string.letters + string.digits

    if args:
        try:
            length = (int)(args[0])
        except ValueError as err:
            print str('length muse be an integer')
            sys.exit(2)
        if not length > 0:
            print str('length must be a positive number')
            sys.exit(1)
    else:
        length = DEFAULT_LENGTH

    print(random_str(selection, length))

def usage():
    print('''Usage: random-str [-uld] [length]
Options:
    -u, --uppercase\tInclude upper case letters
    -l, --lowercase\tInclude lower case letters
    -d, --digits\tInclude digits
    ''')

def random_str(selection, length):
    return ''.join(random.choice(selection) for i in xrange(length))


if __name__ == '__main__':
    main()