templates.md

Templates

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Free-form output with column references, conditionals, and loops. Add template: to a config or use -t on the command line.

Contents

• Syntax — {{var}}, conditionals, repeat
• Inline field specs — modifiers, ranges, enums inside {{}}
• Single-line
• Multiline
• Conditionals
• Repeat
• Serial — {{serial}} counter
• Inline templates (CLI)

Syntax

Syntax	Meaning
{{var}}	Column value (declared) or inline field (registry lookup)
{{field:mod:range}}	Inline with field spec syntax
{{serial}}	Built-in: 0-based record counter (always available)
{{#if var == "val"}}	Conditional start
{{#elif var == "val"}}	Else-if branch
{{else}}	Else branch
{{/if}}	End conditional
{{#repeat N}}	Repeat block N times
{{/repeat}}	End repeat

Declared columns vs inline generation. {{name}} resolves in order: declared column, then field registry. Declared = stable per record (same everywhere). Inline = fresh value each use.

Tag-only lines. Lines containing only block tags and whitespace produce no output.

Nesting. {{#if}} and {{#repeat}} nest to any depth.

Inline field specs

Any {{placeholder}} that is not a declared column is looked up in the field registry. Inline fields accept the same spec syntax as columns and CLI — modifiers, ranges, lengths:

template: |
  [{{timestamp:log}}] src={{ip}} pid={{integer:1000..32768}} msg={{base64:short}}
  user={{username}} card={{credit-card:space}} code={{digits:4}}
  date={{date:2020..2025}} amount={{amount:usd}} lat={{float:0..90}}
  level={{enum:INFO=7,WARN=2,ERROR=1}}

Each inline field generates a fresh value per occurrence. To reuse a value, declare it in columns: and reference by name.

Single-line

template: '{{ip}} - {{user}} [{{ts}}] "{{method}} {{path}} HTTP/1.1" {{status}}'

seedfaker ip user ts=timestamp:log method=http-method path=url status=http-status \
  -t '{{ip}} - {{user}} [{{ts}}] "{{method}} {{path}} HTTP/1.1" {{status}}' -n 5

Multiline

YAML | block. Records separated by blank lines.

columns:
  from: name
  from_email: email
  to: name
  body: message

template: |
  From: {{from}} <{{from_email}}>
  To: {{to}} <{{email}}>

  {{body}}
  — {{from}}

{{from}} appears twice — same value both times. {{email}} in the To: line is inline (not declared in columns) — generates a fresh value.

Conditionals

{{#if}} checks a declared column with == or !=. Inline fields cannot be used in conditions.

columns:
  level: enum:INFO=7,WARN=2,ERROR=1
  msg: message
  ip: ip

template: |
  {{#if level == "ERROR"}}
  ALERT: {{msg}} — source: {{ip}}
  {{#elif level == "WARN"}}
  WARN: {{msg}}
  {{else}}
  {{level}}: {{msg}}
  {{/if}}

Repeat

{{#repeat N}} repeats a section within a single record (max 1000). Inline fields generate fresh values per occurrence.

columns:
  team: company-name
  lead: name

template: |
  Team: {{team}}, Lead: {{lead}}
  {{#repeat 5}}
  - {{name}} <{{email}}>
  {{/repeat}}

Serial

{{serial}} — 0-based record counter. Always available, no declaration needed. Not affected by seed.

seedfaker name -t '{{serial}}: {{name}}' -n 3 --seed demo --until 2025
# 0: Paulina Laca
# 1: Irene Michaelides
# 2: Elvira Castro Gonzalez

Do not declare serial in columns: — it is reserved.

Limits

• {{#repeat N}} — maximum N is 100
• {{#if}} and {{#repeat}} can be nested up to 30 levels deep

Related guides

• Reproducible datasets — template-based deterministic fixtures

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