find, locate, whereis, which, type

I suspect that most Linux admins know 3 or 4 of these five commands, and regularly use 2 or 3 of them.

linuxhaxor has a useful introduction to all five, with the most common uses for each of them.

Note that locate requires a regular run of updatedb – the article says that “The database is automatically created and updated daily” which is true for most distributions, but it depends on your cron setup – you can update the locate db as frequently as you wish. Another thing to note about locate is that it will not use the (normally root-generated) database to tell you (as a non-privileged user) about files which you would not otherwise know about.

get the width of the terminal

A quick and easy way to get the width of your terminal is the command stty size. I have used it with diff like this:

diff -y -W `stty size | cut -d” ” -f2` –suppress-common-lines oldfile newfile

Note: This stty option is not available on Solaris, however, if you have it installed, the /usr/openwin/bin/resize command sets the COLUMNS variable.

update: This post originally said “width of your Linux terminal” but as noted in the comments, this feature of stty is also available in *BSD implementations, even though it is not part of the POSIX standard. So you should expect this to work on GNU and BSD systems (eg, most GNU/Linux distros, most *BSDs, including OSX) but not on all POSIX-compliant systems (eg, Solaris). I would assume that AIX, HPUX, SCO, the other “traditional” UNIX systems would also not support this, though I have not (yet) tested any of them. YMMV.