Generate passwords with openssl

write 6 random bits of base64-encoded data. This will produce an eight character string making a good unix (crypt based) password:

$ openssl rand -base64 6
$RcqcGq4h

This is an example used to generate a 16 character password

$ openssl rand -base64 12
$IEoOfT/LKimAf/sd

When random data goes through the base encoding process the string output is always a multiple of 4 possibly padded on the end with one or more '=' characters. So if you want a password that is not a multiple of 4 you need to artifically chop it where you want it.
An example used to generate a 37 character password:
with cut:

$ openssl rand -base64 37 cut -c1-37
$X/UhqF1I9qO57Uz8hPufpvbOLYCeuuvqnerUM

or sed:

$ openssl rand -base64 37 sed -e 's/^\(.\{37\}\).*/\1/g' $sAPpFoGnbXnJrQc8Cl/QqrNwn0QK3hHrgANt1

or awk:

$ openssl rand -base64 37 awk 'BEGIN{FS=""} {for (i=1;i<=37;i++) printf("%s",$i);} {printf "\n"}'
$WhGWSCp8Y2uilxWfOfAyQXa4QqlE78uJeH3sn