Compact bash prompt when using a directory tree / filename

First of all, you might simply want to change the \w with \W. That way, only the name of the current directory is printed and not its entire path:

terdon@oregano:/home/mydirectory1/second_directory_with_a_too_long_name/my_actual_directory_with_another_long_name $ PS1="\u@\h:\W \$ "
terdon@oregano:my_actual_directory_with_another_long_name $ 

That might still not be enough if the directory name itself is too long. In that case, you can use the PROMPT_COMMAND variable for this. This is a special bash variable whose value is executed as a command before each prompt is shown. So, if you set that to a function that sets your desired prompt based upon the length of your current directory's path, you can get the effect you're after. For example, add these lines to your ~/.bashrc:

get_PS1(){
        limit=${1:-20}
        if [[ "${#PWD}" -gt "$limit" ]]; then
                ## Take the first 5 characters of the path
                left="${PWD:0:5}"
                ## ${#PWD} is the length of $PWD. Get the last $limit
                ##  characters of $PWD.
                right="${PWD:$((${#PWD}-$limit)):${#PWD}}"
                PS1="\[\033[01;33m\]\u@\h\[\033[01;34m\] ${left}...${right} \$\[\033[00m\] "
        else
                PS1="\[\033[01;33m\]\u@\h\[\033[01;34m\] \w \$\[\033[00m\] "
        fi


}
PROMPT_COMMAND=get_PS1

The effect looks like this:

terdon@oregano ~ $ cd /home/mydirectory1/second_directory_with_a_too_long_name/my_actual_directory_with_another_long_name
terdon@oregano /home...th_another_long_name $ 

Adding in a character return is my main solution to this

So my prompt (which has other stuff too, making it even longer) looks like this:

You'll notice that the $ is getting returned as a new line

I achieve this with

HOST='\[\033[02;36m\]\h'; HOST=' '$HOST
TIME='\[\033[01;31m\]\t \[\033[01;32m\]'
LOCATION=' \[\033[01;34m\]`pwd | sed "s#\(/[^/]\{1,\}/[^/]\{1,\}/[^/]\{1,\}/\).*\(/[^/]\{1,\}/[^/]\{1,\}\)/\{0,1\}#\1_\2#g"`'
PS1=$TIME$USER$HOST$LOCATION'\n\$ '

Note that, even though on a separate line, super long directory trees such as

/home/durrantm/Dropbox/96_2013_archive/work/code/ruby__rails are shortened to

/home/durrantm/Dropbox/_/code/ruby__rails

i.e. "top 3 directories /_/ bottom two directories" which is usually what I care about

This will make sure that the line never gets too long due to directory tree length. If you always want the full directory tree just adjust LOCATION, i.e.

LOCATION=' \[\033[01;34m\]`pwd`'

Created ~/.bash_prompt:

maxlen=36
# set leftlen to zero for printing just the right part of the path
leftlen=19
shortened="..."
# Default PWD
nPWD=${PWD}
if [ ${#nPWD} -gt $maxlen ]; then
  offset=$(( ${#nPWD} - $maxlen + $leftlen ))
  nPWD="${nPWD:0:$leftlen}${shortened}${nPWD:$offset:$maxlen}"
else
  nPWD='\w'
fi
echo "\u@\h:$nPWD\$ "

Added in my ~/.bash_profile:

function prompt_command {
  export PS1=$(~/.bash_prompt)
}
export PROMPT_COMMAND=prompt_command

Output is:

user@machinename:/home/mydirectory1/...another_long_name$