Truncated $PWD in the command prompt

The script below will truncate the $PWD to 1/4 of the terminal width and put it into the command prompt, all within the same bash process, no forks to tr and gawk.

function truncate_pwd

{

  newPWD="${PWD/#$HOME/~}"

  local pwdmaxlen=$((${COLUMNS:-80}/4))

  if [ ${#newPWD} -gt $pwdmaxlen ]

  then

     newPWD=".+${newPWD: -$pwdmaxlen}"

  fi

}



PROMPT_COMMAND=truncate_pwd

PS1="${ttyname}@\h:\${newPWD}\\$ "