Random string generator on shell

pwgen

#!/usr/bin/env bash

# ref http://d.hatena.ne.jp/pasela/20120710/random
usage() {
  cat << EOF
Usage: ${0##*/} [-l letter_set] [-w word_num] [-n number_of_passwords]

Generates random letters for password.

OPTIONS:
  -l string   Set of letters to be picked up.
  -g regexp   Regexp for 'grep -i'. You MUST define a possible pattern,
              one of the letters in '-l' param for example,
              otherwise never terminate.
  -w integer  Number of letters a password.
  -n integer  Number of passwords to generate.
  -h          Show this message.
EOF

  exit 0;
}

# default
letter_set='0-9A-Za-z_-'
reg='[_-]'
letter_num=16
line=20

while getopts "l:g:w:n:h" opt; do
  case $opt in
    l) letter_set=${OPTARG} ;;
    g) reg=${OPTARG} ;;
    w) letter_num=${OPTARG} ;;
    n) line=${OPTARG} ;;
    h) usage ;;
  esac
done

cat /dev/urandom \
  | LC_CTYPE=C tr -dc $letter_set \
  | fold -w $letter_num \
  | grep -i $reg \
  | head -n $line