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h1. Bash countdown

This uses a few tricks to do what you want:

* The printf command does NOT append a linefeed automatically unless you tell it to.

* Setting IFS to something else lets the shell split things apart into arrays on whatever delimiter you want, in this case , :.

* The date command can be used to produce time in seconds.

* Carriage returns return the cursor to the beginning of the line without moving to the next line.

<pre>

function countdown

{

  local OLD_IFS="${IFS}"

  IFS=":"

  local ARR=( $1 )

  local SECONDS=$((  (ARR[0] * 60 * 60) + (ARR[1] * 60) + ARR[2]  ))

  local START=$(date +%s)

  local END=$((START + SECONDS))

  local CUR=$START

  while [[ $CUR -lt $END ]]

  do

    CUR=$(date +%s)

    LEFT=$((END-CUR))

    printf "\r%02d:%02d:%02d" \

            $((LEFT/3600)) $(( (LEFT/60)%60)) $((LEFT%60))

            sleep 1

  done

  IFS="${OLD_IFS}"

  echo "        "

}

countdown "00:07:55"

</pre>