Copier Features Guide

This template requires Copier 9.17.0 or higher. Here are key features you can use.

--ask Flag

Force re-prompting for specific questions during update, even if already answered. This requires the --skip-answered flag as well, in order to skip all other questions.

# Normal update skips answered questions
copier update -a .copier-answers/devops.yaml

# Force re-prompting for specific questions
copier update --ask artifact_id --ask version -a .copier-answers/devops.yaml --skip-answered

# Combine with other flags
copier update --ask dtr_org -a .copier-answers/devops.yaml --skip-answered

Use case: Change just one or two answers without going through all prompts.

check-update Command

Check if a template update is available without actually updating.

# Check if update available
copier check-update -a .copier-answers/devops.yaml

Git Template Caching

Remote templates are cached as local Git mirrors for faster subsequent operations.

# First run - clones template (slower)
copier copy https://coderepo.mobilehealth.va.gov/scm/ckm/ngss-devops-template.git ./my-project

# Subsequent runs - uses cached mirror (much faster)
copier update -a ./my-project/.copier-answers/devops.yaml ./my-project

# Cache location
ls ~/.cache/copier/  # Linux
ls ~/Library/Caches/copier/  # macOS

User Settings

Configure default answers and trusted repositories.

~/.config/copier/settings.yml (Linux) or ~/Library/Application Support/copier/settings.yml (macOS)

# Define default answers applied to all templates
defaults:
  author_name: James Hockley
  author_email: james@example.com
  dtr_org: ckm

# Trust specific template sources (no --trust needed)
trust:
  - https://coderepo.mobilehealth.va.gov/*
  - /Users/dallas/IdeaProjects/*

The trust feature may not work for all CLI invocations. Use --trust flag as a fallback.

StrictUndefined Mode

This template uses strict mode to catch undefined variables.

# In copier.yaml
_envops:
  undefined: strict

If a template references an undefined variable, you’ll get a clear error message instead of a silent empty string.

Better Error Messages

Invalid choice errors now show the variable name and valid options:

Error: Invalid choice for 'database': 'mongodb'
Valid choices are: postgresql, mysql, sqlite

Executable Bit Propagation

Executable permissions are correctly preserved during updates, even with git core.fileMode=false.

Data Files

Pass additional data without re-prompting:

# Create a data file
cat > dependencies.yaml << EOF
service_dependencies:
  - ckm/service-a:v2.0.0
  - ckm/service-b:v1.5.0
EOF

# Update with the data file
copier update -a .copier-answers/devops.yaml --data-file dependencies.yaml

Useful Copier Commands

# Copy template to new project
copier copy <template> <destination>

# Update existing project
copier update -a .copier-answers/devops.yaml

# Update with specific version
copier update --vcs-ref v1.2.0 -a .copier-answers/devops.yaml

# Force all defaults (non-interactive)
copier update --defaults -a .copier-answers/devops.yaml

# See what would change (dry run)
copier update --pretend -a .copier-answers/devops.yaml

# Skip specific questions
copier update --skip-answered --ask version -a .copier-answers/devops.yaml