feat: add til how to use default values in docker compose yml

fixes: #153

Taskfile.yml

@@ -11,7 +11,7 @@ tasks:
 
   new_post:
     cmds:
-      - scripts/add "{{.CLI_ARGS}}"
+      - new_post "{{.CLI_ARGS}}"
 
   new_talk:
     cmds:

content/posts/2023-12-30-til-how-to-use-default-values-in-docker-compose-yml/index.md

@@ -0,0 +1,42 @@
+---
+title: "TIL: How to Use Default Values in docker-compose.yml"
+date: 2023-12-30
+canonicalURL: https://haseebmajid.dev/posts/2023-12-30-til-how-to-use-default-values-in-docker-compose-yml
+tags:
+  - docker-compose
+  - bash
+series:
+  - TIL
+---
+
+**TIL: How to Use Default Values in docker-compose.yml**
+
+Sometimes we want to use env variables in our docker-compose files like so:
+
+```yml
+services:
+    client:
+        image: ${CI_DEPENDENCY_PROXY_GROUP_IMAGE_PREFIX}/nginx
+        ports:
+            - 8000:80
+```
+
+Here we are going to use the GitLab CI dependency proxy to pull our Nginx image, so we can speed up our pipelines but 
+also avoid being rate limited by docker hub. However, when running this locally, we will need to make sure the 
+`CI_DEPENDENCY_PROXY_GROUP_IMAGE_PREFIX` env variable is set. Which just adds a bit more work, instead we can leverage
+some of the special syntax docker-compose provides [^1], which I think it inherits from bash.
+
+Where we can use interpolation to set default values if the env variable is not set:
+
+```yml
+services:
+    client:
+        image: ${CI_DEPENDENCY_PROXY_GROUP_IMAGE_PREFIX:-docker.io}/nginx
+        ports:
+            - 8000:80
+```
+
+In this case, `:-` will use docker.io if the env variable is not set or is empty. There are several other variations 
+you can find in the footnote below.
+
+[^1]: https://docs.docker.com/compose/environment-variables/env-file/

flake.nix

@@ -11,6 +11,24 @@
         pkgs = nixpkgs.legacyPackages.x86_64-linux;
       in
       pkgs.mkShell {
+        new_post = pkgs.writeScriptBin "new_post" ''
+          #!/usr/bin/env bash
+
+          TITLE=$(gum input --prompt "Post title:")
+          USER_DATE=$(gum input --prompt "Date to publish YYYY-MM-DD:")
+
+          TITLE_SLUG="$(echo -n "$TITLE" | sed -e 's/[^[:alnum:]]/-/g' | tr -s '-' | tr A-Z a-z | tail -c +2 | head -c -1)"
+          DATE="$(date +"%F")"
+          SLUG="$DATE-$TITLE_SLUG"
+
+          git checkout -b "$SLUG"
+          hugo new --kind post-bundle posts/$SLUG
+
+          echo "Creating OG for content/posts/$SLUG"
+          python scripts/og/generate.py content/posts/$SLUG
+          rm content/posts/$SLUG/images/.gitkeep
+        '';
+
         generate_og = pkgs.writeScriptBin "generate_og" ''
           python ./scripts/og/generate.py
         '';
@@ -19,6 +37,7 @@
           hugo
           python3
           go-task
+          gum
         ];
       };
   };