countdown in shell without seq or jot - shell

Question

I'm trying to make a countdown timer script that takes a number of seconds as $1, then counts down to zero, showing the current remaining seconds as it goes.
The catch is, I'm doing this on an embedded box that doesn't have seq or jot, which are the two tools I know can generate my list of numbers.
Here's the script as I have it working on a normal (non-embedded) system:
#!/bin/sh
for i in $(/usr/bin/jot ${1:-10} ${1:-10} 1); do
printf "\r%s " "$i"
sleep 1
done
echo ""
This works in FreeBSD. If I'm on a Linux box, I can replace the for line with:
for i in $(/usr/bin/seq ${1:-10} -1 1); do
for the same effect.
But what do I do if I have no jot OR seq?

Answer 1

The problem with "vanilla" Bourne shell is that there's no such thing; the behavior depends on the particular implementation. Most modern /bin/shes have POSIX features, but differ in the details. I have a habit of falling back to really ancient Bourne features when I go into "sh-compatibility" mode, which was helpful 30 years ago but is usually overboard on modern systems, even embedded ones. :)
Anyway, here's a generic countdown loop that works even in very old shells, yet still works fine in modern bash/dash/ksh/zsh/etc. It does require the expr command, which is a pretty safe requirement.
i=10
while [ $i -gt 0 ]; do
...
i=`expr $i - 1`
done
So if your embedded system has printf, here's your script, with the same "default to 10 if no argument specified" behavior:
#!/bin/sh
n=$1
i=${n-10}
while [ $i -gt 0 ]; do
printf '\r%s ' "$i"
i=`expr $i - 1`
sleep 1
done
(The first two lines can probably be replaced with just i=${1-10}, but some - again, ancient - shells didn't like applying special parameter expansions to numeric parameters.)
If the system doesn't have printf, then it becomes problematic; with only the shell's built-in echo (or no builtin and some randomly selected implementation of /bin/echo), there's no guaranteed way to do either of those things (echo a special character or prevent the newline). You might be able to use \r or \015 to get the carriage return. You might need -e to get the shell to recognize those (but that might just wind up echoing a literal -e). Putting a literal carriage return inside the script will probably work but makes maintaining the script a pain.
Similarly, -n might squash the newline, but might just echo a literal -n. The earliest way to squash newlines with echo used the special sequence \c where the newline would naturally go; this still works with some versions of /bin/echo (including the one on Mac OS X) or in conjunction with bash's builtin echo's -e option.
So what seems to be the simplest part of the script might be the part that makes you reach for awk.

Answer 2

If your shell was bash, you could count down from a fixed number with something like this:
#!/bin/bash
for n in {10..1}; do
printf "\r%s " $n
sleep 1
done
But that won't work for you, because bash won't handle things like {${1:-10}..1}, and you've specified you want a command line option.
Of course, you've also said you're not using bash, so we'll assume a simpler shell.
If you have awk, you can use that to count.
#!/bin/sh
for n in $(awk -v m="${1:-10}" 'BEGIN{for(;m;m--){print m}}'); do
printf "\r%s " $n
sleep 1
done
printf "\r \r" # clean up
If you don't have awk, you should be able to do it in pure shell:
#!/bin/sh
n=${1:-10}
while [ $n -gt 0 ]; do
printf "\r%s " $n
sleep 1
n=$((n-1))
done
printf "\r \r" # clean up
I think the pure-shell version is probably simple enough that it should be preferred over the awk solution.
Of course, as Mark Reed pointed out in comments, if your system doesn't include a printf, then you'll need to perform some ugly echo magic that will depend on your OS or shell... and if your shell doesn't support $((..)), you can replace that line with n=$(expr $n - 1). If you want to add error handling in case a non-numeric $1 is provided, that wouldn't hurt.

Answer 3

If you're using Bash, this is what you want:
for i in {1..10}
Or no bash? How about the stuff from this post? Bourne Shell For i in (seq)
try
for i in 1 10 15 20
do
echo "do something with $i"
done
else if you have recent Solaris, there is bash 3 at least. for example
this give range from 1 to 10 and 15 to 20
for i in {1..10} {15..20}
do
echo "$i"
done
OR use tool like nawk
for i in `nawk 'BEGIN{ for(i=1;i<=10;i++) print i}'`
do
echo $i
done
OR even the while loop
while [ "$s" -lt 10 ]; do s=`echo $s+1|bc`; echo $s; done