Feature: Dynamically added env variables

[michaszcz]

I'd like to have some option to set env variables dynamically for all steps of the task.

Example 1:

version: '3'

tasks:
  greet:
    cmds:
      - export GREETING=Hello
      - echo $GREETING  # Currently it'll print an empty string, I'd like to receive the value `Hello`

Example 2:

version: '3'

tasks:
  task_name:
    dynamic_env:  # Currently not possible
      sh: python script_that_exports_env_variables.py
    cmds:
      - echo $DYNAMIC_VAR1 $DYNAMIC_VAR2  # Env vars set by the script

Without the feature I have to export variables and use them in one step - example:
Example 2:

version: '3'

tasks:
  task_name:
    cmds:
      - ./export_vars.sh && echo $DYNAMIC_VAR1 $DYNAMIC_VAR2
      - echo $DYNAMIC_VAR1 $DYNAMIC_VAR2  # Currently vars are not available in this step

[vmaerten]

This is possible to set dynamic env variable but only one at the same time :

version: '3'

tasks:
  greet:
    env:
      GREETING: {sh: echo 'hello'}
      FOO: bar
    cmds:
      - echo $GREETING

If you want to add multiple env variable at the same time, I would use dotenv files and follow this issue : #1381

[michaszcz]

Even if dotenv were available, it would still have a few issues:

1. It would require generating a dotenv file and removing it after task execution, which could cause issues in parallel execution.
2. Environment variables must remain the same throughout the task's execution.