Env variable not found by R in Azure Pipeline - r

Question

I'm trying to convert my Travis-based tests to Azure Pipelines, and I'm running into a problem where R doesn't seem to pick up an environment variable.
Here is the yaml:
trigger:
- master
variables:
- group: GH
- name: R_LIBS_USER
value: '$(Agent.BuildDirectory)/R/library'
- name: containerImage
value: rocker/rstudio:latest
pool:
vmImage: 'ubuntu-latest'
container: rocker/rstudio:latest
steps:
- script: |
echo 'options(repos = "https://cloud.r-project.org")' > ~/.Rprofile
mkdir -p ${R_LIBS_USER}
displayName: 'Setup R library directory'
- bash: |
Rscript -e "install.packages(c('remotes', 'rcmdcheck'))" <-- problem here
Rscript -e "remotes::install_deps(dependencies=TRUE)"
displayName: 'Installing package dependencies'
- bash: |
Rscript -e "rcmdcheck::rcmdcheck(args = '--no-manual', error_on = 'error', check_dir = 'check')"
displayName: 'Checking package'
The problem is in the bash step where I install the remotes and rcmdcheck packages, and then run install_deps. For some reason R doesn't see the R_LIBS_USER variable, which should expand to something like /__w/1/R/library. Because of this, it tries to install to the site-wide location /usr/local/lib/R/site-library, which fails because this directory is not user-writeable.
What's happening here?

Answer 1

For whatever reason, R just can't see the environment variable R_LIBS_USER. What finally worked for me was editing the ~/.Rprofile config file to include the user library directory:
steps:
- script: |
echo 'options(repos = "https://cloud.r-project.org")' > ~/.Rprofile
echo ".libPaths(c('$R_LIBS_USER', .libPaths()))" >> ~/.Rprofile
mkdir -p $(R_LIBS_USER)
displayName: 'Setup R library directory'
Now I just need to figure out how to avoid reinstalling several megabytes of dependencies on each run....