shell: log directory rotation, more compact code avoiding code duplication - bash

Question

in my shell scripts I need to rotate log directories.
I am looking for a more compact, scaleable and elegant way than this, but have currently no idea how to solve this i.e. in a while loop and to calculate with variables.
function f_rotate_logdirs()
{
if [ -d $LOGDIR_OLD14 ]; then
# be extra cautious, no rm -rf operation ...
rm -rf $LOGDIR_OLD14
fi
if [ -d $LOGDIR_OLD13 ]; then
mv $LOGDIR_OLD13 $LOGDIR_OLD14
fi
[...]
if [ -d $LOGDIR_OLD1 ]; then
mv $LOGDIR_OLD1 $LOGDIR_OLD2
fi
if [ -d $LOGDIR ]; then
mv $LOGDIR $LOGDIR_OLD1
fi
mkdir -p $LOGDIR
echo $DATE > $LOGDIR/0.DATE
}
Do you have an idea for a more compact code which easily scales up to n_days ?
Any help on this would be much appreachiated.
Many thanks for this upfront.

Answer 1

The following works:
rm -r -f LOGDIR15
seq 1 14 | tac | xargs -t -n1 sh -c 'if [ -d "$1$2" ]; then mv -n "$1$2" "$1$(($2+1))"; fi' -- LOGDIR
if [ -d "LOGDIR" ]; then mv -n "LOGDIR" "LOGDIR1"; fi
mkdir LOGDIR
We need to handle the first and last separately. Making a function out of it, would be:
backup() {
rm -r -f "$1$2"
seq 1 "$(($2 - 1))" | tac |
xargs -t -n1 sh -c 'if [ -d "$1$2" ]; then mv -n "$1$2" "$1$(($2+1 ))"; fi' -- "$1"
if [ -d "$1" ]; then mv -n "$1" "$1"1; fi
mkdir "$1"
}
with usage:
backup LOGDIR 15
would move the directory named LOGDIR to LOGDIR1 and LOGDIR2 and .. LOGDIR15.
It seems unknown to me, why you use variables $LOGDIR_OLD15 and not just directory names themselves.

Answer 2

Thanks for your input, the commands seq and tac were new to me.
Now I found some time to code it newly and I took some of your nice ideas.
My aim was to get a scaleable solution which is easy to understand and maintain.
I decided to name the current logdir "$dir.0" because some of my scripts gather config diffs of devices that are being taking on daily basis. This makes coding a little bit easier for getting the diffs between i.e. "5 and 3 days ago" or between "2 days ago and today".
#! /bin/sh
# Customizeable settings
LOGDIR_BACKUPS=14 # max number of backups
# Directories
LOGDIR_NAME=logs
LOGDIR=$LOGDIR_NAME.0
# Defines
DATE=`date +'%Y%m%d-%H%M'`
function f_rotate_logdirs() {
local dir=$1 # name of logdir folder
local max=$2 # max #
local min=0 # $dir.0 = current logdir
for i in `seq $min $max | tac`
do
case $i in
$max) if [ -d $dir.$i ]; then
rm -f $dir.$i/*
rmdir $dir.$i
fi
;;
$min) if [ -d $dir.$i ]; then
mv $dir.$i $dir.$((i+1))
fi
mkdir $dir.$i
echo $DATE > $dir.$i/0.DATE
;;
*) if [ -d $dir.$i ]; then
mv $dir.$i $dir.$((i+1))
fi
;;
esac
done
}
f_rotate_logdirs $LOGDIR_NAME $LOGDIR_BACKUPS