What I couldn’t find is a complete example that helped me understand what was going on and worked properly on OS X.

Here’s what I did, and maybe you’ll find it useful.

ESC="\033" # This is the escape sequence
NO_COLOR="$ESC[0m"
IRED="$ESC[1;31m" # ANSI color code for intense/bold red
IGRN="$ESC[1;32m" # ANSI color code for intense/bold green

# From http://railstips.org/blog/archives/2009/02/02/bedazzle-your-bash-prompt-with-git-info/
# I had to change 'git-symbolic-ref' to 'git symbolic-ref'
function parse_git_branch {
  ref=$(git symbolic-ref HEAD 2> /dev/null) || return
  echo " ["${ref#refs/heads/}"]" # I wanted my branch wrapped in [], use () or <> or whatever
}

# from http://ariejan.net/2010/04/25/ruby-version-and-gemset-in-your-bash-prompt-yes-sir
function rvm_version {
  local gemset=$(echo $GEM_HOME | awk -F'@' '{print $2}')
  [ "$gemset" != "" ] && gemset="@$gemset"
  local version=$(echo $MY_RUBY_HOME | awk -F'-' '{print $2}')
  [ "$version" != "" ] && version="$version"
  local full="$version$gemset"
  [ "$full" != "" ] && echo "${full}:" # the colon at the end is a delimiter, you could use a space instead
}

#PS1="\h:\W \u\$" # For reference, here's the default OS X prompt
#export PS1="\$(rvm_version)\W \$(parse_git_branch)\$ " # Without the colors

# I had to put the \[ and \] down here, as opposed to $IRED, to avoid wrapping funkiness.
export PS1="\[$IRED\]\$(rvm_version)\[$NO_COLOR\]\W\[$IGRN\]\$(parse_git_branch)\[$NO_COLOR\] \$ "

I encountered all kinds of weirdness getting the colors to work. The problems all centered around getting the \[ and \] correct. If you’re having problems where the wrapping is wrong, or arrow keys or the backspace causes your prompt to disappear, check your \[\]‘s. The rule of thumb is the characters you’re escaping should be wrapped in them. Keep in mind, the color codes don’t seem to include a ] at the end.

I got my color codes from here. At the bottom of that page is a dandy script which prints out all the colors and backgrounds making it easy to find a good color combination for your terminal.

References:
Ruby version and gemset in your Bash prompt? Yes sir!
Bedazzle Your Bash Prompt with Git Info

#!/bin/bash
if [[ $EUID -eq 0 ]]; then
  echo "Don't run as root!"
  exit 1
fi

Enter the Bash Launcher Loop:

#!/bin/bash

# maximum number of attempts to launch
max_launches=2
# maximum number of launches allowed in $reset seconds
runaway_max=8
# minimum
min_seconds=1
# number of seconds to let process run before reset
reset_seconds=10

# number of attempts to launch
launch_attempts_count=0
start_time=`date +%s`

while true; do

  echo "Executing ($launch_attempts_count)..."
#  sleep 1

  # increment the number of launch attempts
  launch_attempts_count=$(($launch_attempts_count+1))
  # get the number of seconds since the start time...
  time=$((`date +%s`-$start_time))
  # if we launched more than $max_launches in less than $min_seconds, then
  # for some reason the process can't start, so exit
  if [ $launch_attempts_count -gt $max_launches -a $time -lt $min_seconds ]; then
    echo "Too many launches!"
    exit 1
  fi
  # If we haven't exceeded the threshold for failed starts, but
  # the process isn't running long enough to reset the counters,
  # we can guess there's a problem that keeps causing the process
  # to crash, so we should probably give up for now
  if [ $launch_attempts_count -gt $runaway_max ]; then
    echo "Process keeps crashing"
    exit 1
  fi
  # If the process has been running for more than $max_seconds, then
  # we're going to assume it was working properly, so reset the counters.
  # Normally, $max_seconds would be set to something like 3600 (1 hour).
  if [ $time -gt $reset_seconds ]; then
    launch_attempts_count=0
    start_time=`date +%s`
  fi

done

The script above will stop trying to launch the process if:

• if there are more than 2 launch attempts in 1 second (printing “Too many launches!)
• if there are more than 8 launch attempts in 10 seconds (printing “Process keeps crashing!)

If the process is relaunched less than 8 times in 10 seconds, the $start_time and $launch_attempts_count will be reset, thus starting over.

To see this in action just run the script like it is, and the output will be:

Executing (0)...
Executing (1)...
Executing (2)...
Too many launches!

Now uncomment line 19 (# sleep 1), and the output will be:

Executing (0)...
Executing (1)...
Executing (2)...
Executing (3)...
Executing (4)...
Executing (5)...
Executing (6)...
Executing (7)...
Executing (8)...
Process keeps crashing

Finally, change line 19 from sleep 1 to sleep 2, and the output will be:

Executing (0)...
Executing (1)...
Executing (2)...
Executing (3)...
Executing (4)...
Executing (5)...
Executing (0)...
Executing (1)...
Executing (2)...
Executing (3)...
Executing (4)...
Executing (5)...
Executing (0)...

And so on, until you hit ctrl+c.

Obviously those values are just for demo purposes. Better production values would be:

max_launches=2
runaway_max=2
min_seconds=1
reset_seconds=3600

This tells the script to exit if there are more than two launch attempts in one second or more than two in one hour, otherwise it will just keep running.

Anywho, I modified it like so:

#!/usr/bin/env bash
output=`md5 "$1"`
echo `echo $output | sed -e 's/MD5 (\(.*\)) = \(.*\)/\2  \1/'`

I’m sure the openssl md5 command would work still as well as the md5 command. They both output something similar to:

MD5 (my_file.txt) = caff1120584b95432eed1e84cb99a593

That’s where the sed thing comes in handy, to convert it to:

caff1120584b95432eed1e84cb99a593  my_file.txt