Arguments and environment variables

Basic usage

You can use ${arg:<name>:<default>} and ${env:<name>:<default>} expressions pretty much everywhere across welder.yaml files. ${arg:<name>:<default>} is used to get arguments passed to the build script. ${env:<name>:<default>} is used to get environment variables from the host environment (e.g. $HOME).

Example:

${arg:build-parameters:}

Arguments

schemaVersion: 1.8.0
tasks:
  hello:
    image: ubuntu
    env:
      NAME: "${arg:name:John Doe}"
    script:
      - echo "HELLO $NAME!"

on-host:~$ welder run hello
run [hello]  - Running 1 scripts on host...
run [hello]  - Executing script: 'echo "HELLO $NAME!"'
run [hello] HELLO John Doe!
run [hello]  - Finished hello in 0s

on-host:~$ welder run hello -a name="Ilia"
run [hello]  - Running 1 scripts on host...
run [hello]  - Executing script: 'echo "HELLO $NAME!"'
run [hello] HELLO Ilia!
run [hello]  - Finished hello in 0s

Environment variables

Welder allows to read environment variables from the host environment using ${env:<name>:<default>} expression.

schemaVersion: 1.8.0
tasks:
  say-hello:
    image: alpine:latest
    env:
      NAME: "John Doe"
    script:
      - echo "Hello, ${env:NAME} (aka ${NAME})!"

Simple run of welder run say-hello will result in the following output:

on-host:~$ NAME=Peter welder run say-hello 
run [say-hello]  - Running 1 scripts in container 'alpine:latest'...
run [say-hello] Hello, Peter (aka John Doe)!
run [say-hello]  - Finished say-hello in 3s

Note the difference between ${env:NAME} and ${NAME} (the latter is a variable within container whereas the former is taken from the host environment).