System Variables

CXL provides several system variable namespaces prefixed with $. These give CXL expressions access to pipeline execution context, user-defined variables, per-record metadata, and the current time.

$pipeline.* – Pipeline context

Pipeline variables are accessed via $pipeline.member_name. Some are frozen at pipeline start; others update per record.

Stable (frozen at pipeline start)

$ cxl eval -e 'emit name = $pipeline.name' \
    -e 'emit exec = $pipeline.execution_id'

{
  "name": "cxl-eval",
  "exec": "00000000-0000-0000-0000-000000000000"
}

Counters

trace info if $pipeline.total_count % 10000 == 0 then "processed " + $pipeline.total_count.to_string() + " records"

$source.* – Per-record source lineage

$source.* exposes engine-stamped columns that travel with every record from its origin Source node downstream through merges, combines, and transforms. They identify where the record came from and when in event-time it happened. All three columns are filtered out of default Output projections — reference them explicitly with emit if you need them in your output schema.

filter $source.name == "src_web"
emit origin = $source.name
emit ingest_file = $source.file
emit ts = $source.event_time

$source.event_time is the column a time-windowed aggregate reads to assign records to windows. It is only populated for records from a source that declares watermark: — otherwise it holds Null.

$vars.* – User-defined variables

User-defined variables are declared in the YAML pipeline config under pipeline.vars: and accessed via $vars.name in CXL expressions.

YAML declaration

pipeline:
  name: invoice_processing
  vars:
    high_value_threshold: 10000
    tax_rate: 0.21
    output_currency: "USD"
    fiscal_year_start_month: 4

CXL usage

filter amount > $vars.high_value_threshold
emit tax = amount * $vars.tax_rate
emit currency = $vars.output_currency

Variables provide a clean way to externalize configuration from CXL logic. Combined with channels, different variable sets can parameterize the same pipeline for different environments or clients.

$meta.* – Per-record metadata

Metadata is a per-record key-value store that travels with the record through the pipeline but is not part of the output columns. Write to it with emit meta; read from it with $meta.field.

Writing metadata

emit meta quality = if amount < 0 then "suspect" else "ok"
emit meta source_system = "legacy_erp"

Reading metadata

Downstream nodes can read metadata:

filter $meta.quality == "ok"
emit audit_system = $meta.source_system

Metadata is useful for tagging records with quality flags, routing hints, or audit information that should not appear in the final output unless explicitly emitted.

now – Current time

The now keyword returns the current wall-clock time as a DateTime value. It is evaluated fresh per record, so each record gets the actual time of its processing.

$ cxl eval -e 'emit timestamp = now'

{
  "timestamp": "2026-04-11T15:30:00"
}

now is useful for timestamping records:

emit processed_at = now
emit days_old = now.diff_days(created_date)

Note: now is a keyword, not a function call. Write now, not now().

Complete example

pipeline:
  name: order_enrichment
  vars:
    discount_threshold: 500
    tax_rate: 0.08

  nodes:
    - name: orders
      type: source
      format: csv
      path: orders.csv

    - name: enrich
      type: transform
      input: orders
      cxl: |
        emit order_id = order_id
        emit amount = amount
        emit discount = if amount > $vars.discount_threshold then 0.1 else 0.0
        emit tax = amount * $vars.tax_rate
        emit total = amount * (1 - discount) + tax
        emit processed_at = now
        emit meta source_file = $source.file
        emit pipeline_run = $pipeline.execution_id

    - name: output
      type: output
      input: enrich
      format: csv
      path: enriched_orders.csv