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void.pointer
Asked: 2018-09-13 16:21:48 +0800 CST

How do I know when docker pull updates an image?

  • 772

I have a script that I run to update images and then stop -> rm -> run them again. Unfortunately, the last 3 steps happen even if pull didn't update the image (i.e. it's already up to date). How can I change my bash script so that it only runs the last 3 commands if the pull updated the image?

#!/usr/bin/env bash
set -e

docker pull linuxserver/sonarr
docker stop sonarr
docker rm sonarr
./run-sonarr.sh

docker pull linuxserver/radarr
docker stop radarr
docker rm radarr
./run-radarr.sh

docker pull linuxserver/nzbget
docker stop nzbget
docker rm nzbget
./run-nzbget.sh

docker pull plexinc/pms-docker
docker stop plex
docker rm plex
./run-plex.sh
scripts bash docker 18.04

2 Answers

  1. Best Answer

    You can just check if the string "Image is up to date" is not present:

    ...
export LANG=C
if ! docker pull linuxserver/sonarr | grep "Image is up to date"; then
    docker stop sonarr
    docker rm sonarr
    ./run-sonarr.sh
fi
...
    • 1

  2. You can get the image IDs before and after the pull and compare them:

    docker images --format '{{.ID}}' <your image>

    For instance:

    # ID of current image
~/ >docker images --format '{{.ID}}' tomcat:latest
d636936d0d85

# Pull it (updated this time)
~/ >docker pull tomcat:latest
latest: Pulling from library/tomcat
05d1a5232b46: Pull complete 
5cee356eda6b: Pull complete 
89d3385f0fd3: Pull complete 
65dd87f6620b: Pull complete 
78a183a01190: Pull complete 
1a4499c85f97: Pull complete 
2c9d39b4bfc1: Pull complete 
1b1cec2222c9: Pull complete 
fc95b85a81f3: Pull complete 
0f3868647539: Pull complete 
9b6a6eddb2d9: Pull complete 
8787183cb077: Pull complete 
Digest: sha256:d789f1dc613ef36a24c29f36bdef4891907cd854a5723c73acf6ba78dfc9ac78
Status: Downloaded newer image for tomcat:latest

# ID of new image (different)
~/ >docker images --format '{{.ID}}' tomcat:latest
41a54fe1f79d

# Pull again
~/ >docker pull tomcat:latest
latest: Pulling from library/tomcat
Digest: sha256:d789f1dc613ef36a24c29f36bdef4891907cd854a5723c73acf6ba78dfc9ac78
Status: Image is up to date for tomcat:latest

# Same ID
~/ >docker images --format '{{.ID}}' tomcat:latest
41a54fe1f79d
    • 1