On that note, "pushd /tmp" changes your working directory to /tmp while remembering where you were; "popd" goes back to your previous dir.

Execute your previous command with "!!". Or fetch it with the up arrow key or Control+P.

Know your home directory shortcuts. "cd", "cd ~", or "cd $HOME" all change the current working directory to your home directory.

The -X parameter to ssh enables X forwarding; after "ssh -X user@host", you can run X apps remotely and they'll forward to your X server.

Get an updated list of processes with "top". By default, sorting is based on process IDs. Combine with "-o command" to sort by name instead.

Don't forget tar's support for compressed archives. "tar xvfz" for tar.gz's, "tar xvfj" for .tar.bz2's. (Also, the dash is now optional.)

Need to extract from an archive? Use "tar -xf /path/to/archive". Combine with -v to extract verbosely: "tar -xvf /path/to/archive".

Need to nuke all .DS_Store files on your Mac? "sudo find / -name .DS_Store -depth -exec rm {} \;" will do the trick.

And what if you want to redirect errors to a file? Use "2> /path/to/file". To redirect everything, use "&> /path/to/file".

Output to a file? Append "> /path/to/file" to your command. This overwrites the file, if it already exists. >> appends to the file instead.

"./command &" runs 'command' in the background. Forgot to include the &? Hit CTRL-Z and type in "bg" to run in the background.

On the topic of find, know -size's affixes! "find / -size +20c -size -40k" for files greater than 20 bytes, but less than 40 kilobytes.

"find . -name a*" will list files in the working dir and subdirs whose name begins with "a". Use -size and -type for greater specificity.

Learn your ls! e.g., "ls -lat" will list all files in the directory, incl hidden ones, sorted by date. Combine w/ less: "ls -lat | less".