Disclaimer: I do not use this script on TextDrive, due to resource consumption concerns, and would not recommend anyone else doing so without express permission from TPTB.

#!/usr/bin/env zsh

# keepalive
# 
# This is keepalive, a simple zsh script (may be hackable to work for other
# shells) for keeping things running.
# 
# Usage:
# $ keepalive  [command args]
# $ keepalive ssh -N -L 8080:127.0.0.1:8080
# 
# The next three variables can be edited to adjust the action of the script

# If the command dies ${threshold} times in succession without living more
# than ${min_runtime} seconds the script will quit.
local threshold=5
local min_runtime=60

# The script will sleep ${init_sleep_time} seconds after the first failure,
# ${init_sleep_time}*2 after the second, ${init_sleep_time}*4 times after the 
# third, and so on.
local init_sleep_time=5

# ########################### #
# No need to edit below here. #
# ########################### #
local time_started time_ended 
local sleep_time=${init_sleep_time}
local times_until_fail=${threshold}

until (( times_until_fail <= 0 )); do
  time_started=$(date +%s)
  $*
  time_ended=$(date +%s)

  # reset if it's lived longer than ${min_runtime}
  if (( (${time_ended} - ${time_started}) > ${min_runtime} )); then
    times_until_fail=${threshold}
    sleep_time=${init_sleep_time}
  fi

  (( times_until_fail -= 1 ))
 
  echo
  echo "-- $(date +"%d/%m/%y %H:%M:%S"): \`$*\` died!"
  if (( times_until_fail >= 1 )); then
    echo "-- ${times_until_fail} more executions lasting less than ${min_runtime} seconds will result in job failure."
    echo "-- Sleeping ${sleep_time} seconds..."
    echo
    sleep ${sleep_time}
  fi
  
  (( sleep_time *= 2 ))
done

echo "-- Died too many times in too short a space of time. Exiting!"

Simple, perhaps slightly cryptic oneliner to get the subjects of all flagged messages in a Maildir. It assumes that 'F' is the flag for flagged messages (as it almost always is) and that your message files end with ":2,".

find ~/Maildir -type f -name "*:2,*F*" -exec egrep -h "^Subject:" "{}" ";" | cut -c 10-

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.