Environment variables

On every deployment, PullPreview writes a set of PULLPREVIEW_* variables to /etc/pullpreview/env on the preview instance and uses them throughout the deployment. You can read these values from your pre_script, interpolate them into Compose service definitions, and reference them in Helm inputs.

Available variables

Where they are available

These variables are exposed in three places during a deployment:

• pre_script — every variable above is set in the environment when your pre_script runs, so you can branch on the deployment target, seed data on first run, or print the preview URL.
• Compose environment interpolation — Docker Compose substitutes ${PULLPREVIEW_*} references in your docker-compose.yml from the same environment.
• Helm placeholder expansion — PullPreview expands placeholder tokens in the chart_set, chart_values, and proxy_tls inputs before applying the chart.

Placeholders vs. runtime variables

Helm inputs use a separate set of placeholder tokens that PullPreview expands into the input values before the deployment runs. These are not environment variables — they are template tokens you write in your workflow inputs:

The distinction matters: placeholders are substituted into the input values you pass to the action, while the PULLPREVIEW_* environment variables are available inside the running deployment and your pre_script. See HTTPS and domains for an example of using {{ pullpreview_url }} in proxy_tls.

Compose interpolation example

Reference any variable in a Compose service environment to pass the live preview URL into your app:

services:
  web:
    image: myapp
    environment:
      APP_URL: ${PULLPREVIEW_URL}

Docker Compose resolves ${PULLPREVIEW_URL} from /etc/pullpreview/env at deploy time, so your application always receives the correct scheme, host, and port for the preview.

Seeding on the first run

PULLPREVIEW_FIRST_RUN is the key to running one-time setup. It is true only on the first deployment to an instance, so you can guard expensive operations like database seeding behind it:

if [ "$PULLPREVIEW_FIRST_RUN" = "true" ]; then
  ./bin/seed
fi

See seeding data for the full pattern.