Classic UNIX tips: “Learn 10 good UNIX usage habits
(Break bad UNIX usage patterns)” [slashdot] [digg] [reddit]
Beginner? Look at the short list of UNIX commands.
Need a command-line cookbook? Get the second, revised edition of The Linux Cookbook.
Command-line fu is a huge group database of CLI wisdom.
Winning one-liners (Usenet thread, 1991)
Great ImageMagick one-liners for making text boxes, text images, symbol font graphics, caption and word labels and icons.
The basics: an intro and
community database of tech “recipes”: tutorials on every subject
How to do everything: unix tutorials
Interesting UNIX tools
The classic Useless use of cat award
Linux mailing lists
Plenty of these have good tips.