Retagging docker images without pulling them. Kinda ugly hack, but it works. Requires curl and jq.

docker-retag.sh

#!/bin/bash -e
OLDREPO=youruser/oldrepo
OLDTAG=oldtag
NEWREPO=youruser/newrepo
NEWTAG=newtag
USERPASS='youruser:yourpassword'

TOKEN=`curl -f "https://auth.docker.io/token?service=registry.docker.io&scope=repository:$NEWREPO:push,pull&scope=repository:$OLDREPO:pull" -u "$USERPASS" | jq -r .token`
OLDMANIFEST=`curl -f https://index.docker.io/v2/$OLDREPO/manifests/$OLDTAG -H 'Accept: application/vnd.docker.distribution.manifest.v2+json' -H "Authorization: Bearer $TOKEN"`
NEWMANIFEST=`echo "$OLDMANIFEST" | jq "setpath([\"name\"];\"$NEWREPO\")" | jq --indent 3 "setpath([\"tag\"];\"$NEWTAG\")"`
for layer in `echo "$OLDMANIFEST" | jq -r '.layers[].digest, .config.digest'`; do
    echo "Uploading layer $layer"
    curl -f -X POST "https://index.docker.io/v2/$NEWREPO/blobs/uploads/?mount=$layer&from=$OLDREPO" -H "Authorization: Bearer $TOKEN"
done
curl -D- -X PUT https://index.docker.io/v2/$NEWREPO/manifests/$NEWTAG -H "Content-Type: application/vnd.docker.distribution.manifest.v2+json" -d "$NEWMANIFEST" -H "Authorization: Bearer $TOKEN"