Say you need a quick random 8 character alpha-numeric password. In sh, there isn’t a $RANDOM variable and tr can give different results on different OS’s. More than likely you have perl available - use it!

perl
-le 'print map { (a..z,A..Z,0..9)[rand 62] } 0..pop' 8

Thanks to Chris Angell’s Perl One- Liner page for this one. Do you have a better cross-platform way of doing it? Let me know!