Put the following little snippet in your .bashrc/.bash_profile and you'll have a handy little calculator:

? () { echo "$*" | bc -l; }

Use like this:

bash$ ? 2*2
4

It should be easily modifiable for other shells/calculators.

Via: http://rentzsch.com/rock/longhand

If you want to add a virtualhost on your Mac OS X box without having to wait around for ages, then the easiest way to do so is to shove a line into /etc/hosts and flush the dnscache. Here's a friendly bash function to throw into your .bashrc:

function edithosts {
        if [ -x "`which $EDITOR`" ] || [ -x "`which $1`" ]
        then
                if [ -x "`which $EDITOR`" ]
                then
                        export TEMP_EDIT="`which $EDITOR`"
                else
                        export TEMP_EDIT="`which $1`"
                fi
                echo "* Using ${TEMP_EDIT} as editor"
                $TEMP_EDIT /etc/hosts && echo "* Successfully edited /etc/hosts"
                lookupd -flushcache && echo "* Flushed local DNS cache"
        else
                echo "Usage: edithosts [editor]"
                echo "(The editor is optional, and defaults to \$EDITOR)"
        fi
        unset TEMP_EDIT
}

More simply, you can just flush the DNS cache manually with:

lookupd -flushcache

Or, "How to login over SSH without a password".

First of all, you'll need to have generated an SSH public DSA key using the following commands:

cd ~ && ssh-keygen -t dsa

Then, you can add the following bash function to your .bashrc (or similar) and just type 'scpdsa user@hostname' to add your public key to your 'authorized_keys' file on the server.

function scpdsa {
  if [[ -z "$1" ]]; then
    echo "!! You need to enter a hostname in order to send your public key !!" 
  else
    echo "* Copying SSH public key to server..." 
    ssh ${1} "mkdir -p ~/.ssh && cat - >> ~/.ssh/authorized_keys" < ~/.ssh/id_dsa.pub
    echo "* All done!"
  fi
}

-- updated to use simpler and quicker method.

This is just a simple colored bash prompt which differentiates nicely between normal and root users.

To use this put it in ~/.bashrc, or for it to apply systemwide, in /etc/profile

if [ "$TERM" != 'dumb' ] && [ -n "$BASH" ] && [ -n "$PS1" ]
then
        if [ `/usr/bin/whoami` = 'root' ]
        then
                export PS1='\[\033[01;31m\]\h \[\033[01;34m\]\W \$ \[\033[00m\]'
        else
                export PS1='\[\033[01;32m\]\u@\h \[\033[01;34m\]\W \$ \[\033[00m\]'
        fi
fi

Updated: It's now more concise and functionally more sensible.