clean_repo.sh

#!/usr/bin/env bash

# a script to delete all the ancient versions of a repository generally generated by continious integration tools

if [[ $# -ne 1 ]] ; then
    echo "put your repository to clean as argument (you can just put a part of its name to find it)"
    exit 1
fi

# find max tag of a repository

tags=`docker images | sed -n /$1/p | awk '{print $2}'`
max=0
for i in $tags; do
    # [, ], [[, ]], and operators should be surrounded by space
    # =~ regular expression match operator
    if [[ $i =~ ^[0-9]+$ && $i -gt $max ]] ; then
        max=$i
    fi
done

# delete all the ancient tags

# awk -v max="$max": assign the value of shell variable max to awk variable max
ids=`docker images | sed -n /dashboard/p | awk -v max="$max" '{if($2 < max) print $3}'`
cnt=0
for id in $ids; do
    docker rmi $id
    # use expr to do arithmetic operations
    cnt=`expr $cnt + 1`
done
if [[ $cnt -gt 1 ]] ; then
    echo $cnt images deleted.
elif [[ $cnt -eq 1 ]] ; then
    echo $cnt image deleted.
else
    echo repository was already clean, no image deleted.
fi