Parameters & Precedence

Simple rule: define sensible defaults in the template, store what you ran in the project, and override with the CLI when needed.

Sources and Precedence

Lowest to highest (last one wins):

  • Descriptor defaults: params: in template_config.yaml.
  • Project‑stored values: saved in project.yaml after a render.
  • CLI overrides: --param KEY=VALUE on render/run.

If a required param has no value after merging, BPM errors out with “Missing required parameters: …”.

Declaring Params (template_config.yaml) 

id: hello
params:
  sample_id:        {type: str,  required: true}
  threads:          {type: int,  default: 8}
  skip_qc:          {type: bool, default: false}
  input_dir:        {type: str,  default: "${ctx.project.name}/inputs"}
render:
  into: "${ctx.project.name}/${ctx.template.id}/"
  files:
    - run.sh.j2 -> run.sh
run:
  entry: run.sh

Notes:

  • Types supported: str, int, float, bool (CLI strings are coerced to these types).
  • ${ctx.*} in defaults: safe to use with ctx.project.* and ctx.template.*. Avoid referencing ctx.params.* inside defaults.
  • Path validation (optional): add exists: file|dir|any on a param to make BPM check the given path exists before rendering. Example: input_dir: { type: str, required: true, exists: dir }
  • Descriptions (optional): add description: "..." to a param; shown by bpm template info.

CLI Overrides (–param)

  • Format: --param KEY=VALUE (repeatable). No spaces around =.
  • Booleans: true/false, 1/0, yes/no, on/off are accepted.

Examples

# Start with defaults → threads=8
bpm template render hello

# Override for this invocation
bpm template render --param threads=16 hello

# Multiple params
bpm template render --param sample_id=NA12878 --param input_dir=/data/in hello

How Values Are Stored

  • Project mode: after a successful render, BPM writes final params to project.yaml under this template’s entry. Subsequent runs reuse them unless you override with --param.
  • Ad‑hoc mode (--out): BPM does not modify project.yaml; it writes bpm.meta.yaml in the output folder with the params used.

Using Params in Templates

Inside Jinja files, access with ``:

# run.sh.j2
#!/usr/bin/env bash
set -euo pipefail
echo "Sample: "
toolX --threads  --in ""

Minimal Precedence Walkthrough

1) Defaults in descriptor: threads=8. 2) You render and later edit project params (or re‑render with overrides): project.yaml now stores threads=12. 3) You render again with CLI: --param threads=20 → final value is 20 for this invocation; project keeps the stored value after render.

Best Practices

  • Mark only truly required params as required: true.
  • Provide conservative defaults when possible.
  • Keep names simple ([a-z0-9_]+) and document meaning in the template README.
  • Avoid putting secrets in params; pass via environment or secrets managers instead.