Below are couple of linux commands I personally think are pretty useful and saves time.

1. sudo !! – This command runs the previously executed command and root. I normally forget to put the ‘sudo’ thing.
2. curl -u youremail:yourpassw -d status=”Yaps!” http://twitter.com/statuses/update.xml – This command is for all the twitter fans around. It updates your twitter status. Yeah! It does.
3. du -sh – Outputs the name and the size of files in the folder. The size is output in human readable form i.e 2.4M and not that geeky stuff we usually see.
4. lsusb and lspci – lsusb lists all the USB devices and lspci lists all the pci devices.
5. grep – This is one command that searches for a pattern and outputs the matching lines . eg grep -n '2:00' /home/yaps/log.txt This command will list the line containing 2:00 and also the line number. This is just one way how you can use grep, else grep is a very powerful utility.
6. dmesg – You just plugged in a USB device and then bam! no response from the linux machine. Then dmesg is what comes to the rescue. How to use?? dmesg | grep -i usb the following command lists all references to USB (universal serial bus) devices in the kernel messages.
7. man – I’d say the baap (Father) of all linux commands. Use it properly and become a linux guru .
8. ^foo^bar – Just forgot to mention this command . This command is for people like me, who make lots of mistakes and then have to type all once again. This command changes foo to bar and executes the previous command. Try it out for yourself.