Ring Buffers with Bash Script

This post is a little bit infantile, since it does present a really, really simple thing, but I wrote the shell code yesterday for a backup script and it seems as I will not need it. So I write it down here so either I do not forget it (who knows when it will come in handy?) or perhaps someone else says: “Hey my script could be much easier using this”. In the next days I will post the code that replaces the code shown in this post, so stay tuned.

Here is a short bash function, that offers you to retrieve the value of the index in a ring buffer for a given position argument:

function ring () {
if (( ($1 % $2) < 0 )); then ringval=$(($2 + ($1 % $2))) else ringval=$(($1 % $2)) fi if (( "$ringval" < 10 )); then echo "0$ringval" else echo "$ringval" fi } function stripzeros () { stripped=${1#"${1%%[!0]*}"} if [ -z "$stripped" ]; then echo "0" else echo $stripped fi } # e.g.: 08 currhour="`date \"+%H\"`" # e.g.; 07 lasthour=$(ring $(($(stripzeros ${currhour})-1)) "24") [/sourcecode] The padding and stripping of zeros could be scripted much more elegantly and reliable, but for representing hours of a day this suffices. If someone creates a general script out of it, please feel free to send it in a comment to me, I will add it to this post.

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