Hi Wisecracker, nice idea for a script..

Here are a couple of remarks, so it could be improved further:

1. The shebang is #!/bin/sh, so the script should conform to Posix Shell Standards and not use bash code..

2.:

Code:

if [ "$1" == "" ] || [ "$2" == "" ]

should be

Code:

if [ "$1" = "" ] || [ "$2" = "" ]

3.

Code:

str_len=`printf "${#countdown}"`

Can be written as:

Code:

str_len=${#countdown}

4.

Code:

str_len=$[ ( $str_len - 1 ) ]

$[ ... ] is deprecated bash code. It should be:

Code:

str_len=$(( str_len - 1 ))

5.

Code:

for n in $( seq 0 1 $str_len )

should be:

Code:

n=0
while [ $n -le $str_len ]; 
do
  ...
  n=$((n+1))
done

6.

Code:

number=`printf "${countdown:$n:1}"`

could be written as number=${countdown:$n:1}, but would still be bash code.
Consider using ${var%"${var#?}"} for example and vary the number of question marks...
Another option would be to replace the for loop with a case statement

Code:

case $countdown in 
  (*[!0-9]*) countdown=30
esac

7.

Code:

echo "printf '\033[1m\033[12;3f$text\033[0m\n\n\n'"

For security and other reasons it is best to not use the format field for uncontrolled data. So perhaps something like:

Code:

echo "printf '\033[1m\033[12;3f%s\033[0m\n\n\n' \"$text\""

8. There should be a wait statement after the last done