BASH - generate random string

cat /dev/urandom | tr -dc '[:alpha:]' | fold -w ${1:-20} | head -n 1

cat /dev/urandom | tr -dc '[:alpha:][:punct:]' | fold -w ${1:-20} | head -n 1

Classes:

Class	Description
alnum	Alphanumeric characters
alnum	Alphanumeric characters
alpha	Alphabetic characters
blank	White space characters
cntrl	Control characters
digit	Numeric characters
graph	Graphic characters
ideogram	Ideographic characters
lower	Lowercase alphabetic characters
phonogram	Phonographic characters
print	Printable characters
punct	Punctuation characters
rune	Valid characters
space	Space characters
special	Special characters
upper	Uppercase alphabetic characters
xdigit	Hexadecimal characters