Agent-Skills.md

Agent Skills: dasel v3 Syntax Reference

Use when querying, modifying, or converting JSON, YAML, TOML, XML, CSV, HCL, or INI with dasel v3. Complete reference for selectors, functions, conditionals, variables, spread operator, type casting, and format-specific patterns.

UncategorizedID: Jamie-BitFlight/claude_skills/dasel-reference

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Jamie-BitFlight/claude_skills
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Skill Metadata

Name
dasel-reference
Description
Use when querying, modifying, or converting JSON, YAML, TOML, XML, CSV, HCL, or INI with dasel v3. Complete reference for selectors, functions, conditionals, variables, spread operator, type casting, and format-specific patterns.

dasel v3 Syntax Reference

Single-binary CLI for querying, modifying, and converting structured data. Replaces jq + yq + xmllint with one unified query syntax across all formats.

Stable version at writing (date: 2026-02-23): v3.2.3

Supported Formats

json, yaml, toml, xml, csv, hcl, ini

Basic Usage

# Query from stdin (format required)
echo '{"foo": "bar"}' | dasel -i json 'foo'

# Query from file via stdin
cat config.yaml | dasel -i yaml 'database.host'

# Modify and output full document
echo '{"port": 3000}' | dasel -i json --root 'server.port = 8080'

# Convert formats
cat data.json | dasel -i json -o yaml

Format Handling

dasel v3 does NOT auto-detect format from file extension. There is no -f/--file flag. Input is always read from stdin. Format must be specified explicitly with -i and/or -o. If only one is given, the other defaults to it. If neither is given, both default to json (configurable via ~/dasel.yaml with default_format key).

Source: internal/cli/query.go:10-11, internal/cli/run.go:37-43, internal/cli/config.go:19-21

Key Flags

-i, --in <format>         Input parser (json, yaml, toml, xml, csv, hcl, ini)
-o, --out <format>        Output parser (defaults to input format)
--root                    Output full document after modification
--var <name>=<value>      Pass variables into query (repeatable)
--compact                 Compact output (no pretty-printing)
--rw-flag <name>=<value>  Read/write flag (e.g., --rw-flag csv-delimiter=;)
--read-flag <name>=<val>  Reader flag (e.g., --read-flag xml-mode=structured)
--write-flag <name>=<val> Writer flag (e.g., --write-flag csv-delimiter=;)
-c, --config <path>       Config file path (default: ~/dasel.yaml)

Core Selectors Quick Reference

| Selector | Syntax | Example | |----------|--------|---------| | Dot notation | foo.bar.baz | cat f.json \| dasel -i json 'foo.bar' | | Array index | [0], [2] | cat f.json \| dasel -i json 'items[0]' | | Array slice | [0:3] | cat f.json \| dasel -i json 'items[0:2]' | | Recursive descent | .., ..name | cat f.json \| dasel -i json '..name' | | All values recursive | ..* | cat f.json \| dasel -i json '..*' | | Object construction | { key1, key2 } | cat f.json \| dasel -i json '{ name, age }' | | Spread | obj... | cat f.json \| dasel -i json '{ defaults..., overrides... }' |

Key Functions Quick Reference

19 built-in functions in DefaultFuncCollection (source: execution/func.go:12-33) plus the sortBy complex expression.

| Function | Purpose | Example | |----------|---------|---------| | filter(pred) | Filter arrays | users.filter(active == true) | | map(expr) | Transform arrays | users.map(name) | | each(expr) | Modify each element | each($this = $this * 2) | | search(pred) | Recursive search | search(has("id")) | | sortBy(expr) | Sort array | sortBy($this, desc) | | has(key) | Check key exists | has("name") | | get(key) | Get value at key/index | get("name") | | contains(val) | Check slice contains value | contains(42) | | len(expr) | Length | len($this) | | join(sep) | Join to string | join(",") | | sum(expr) | Sum numeric array | sum($this) | | add(args...) | Add numbers | add(1, 2, 3) | | max(args...) | Maximum value | max(1, 5, 3) | | min(args...) | Minimum value | min(1, 5, 3) | | merge(args...) | Merge maps | merge(defaults, overrides) | | keys(expr) | Get map keys | keys($this) | | reverse(expr) | Reverse array | reverse($this) | | typeOf(expr) | Get type string | typeOf($this) | | toString(expr) | Cast to string | toString($this) | | toInt(expr) | Cast to integer | toInt($this) | | toFloat(expr) | Cast to float | toFloat($this) | | base64e(str) | Base64 encode | base64e("hello") | | base64d(str) | Base64 decode | base64d("aGVsbG8=") | | parse(fmt, data) | Parse data at runtime | parse("json", rawStr) | | readFile(path) | Read file contents | readFile("config.json") | | ignore() | Exclude from branch | ignore() |

Modification Syntax

v3 removed put and delete subcommands. Use assignment with --root:

# Set a value
echo '{"count": 1}' | dasel -i json --root 'count = 42'

# Boolean assignment
echo '{"enabled": false}' | dasel -i json --root 'enabled = true'

# Append to array
echo '[1,2,3]' | dasel -i json --root '[$this..., 4]'

# Remove key (reconstruct without it)
echo '{"keep": "yes", "drop": "no"}' | dasel -i json --root '{ keep }'

Format Conversion

# JSON to YAML
cat data.json | dasel -i json -o yaml

# YAML to TOML
cat config.yaml | dasel -i yaml -o toml

# TOML to JSON
cat config.toml | dasel -i toml -o json

Special Variables

  • $root -- references the root document
  • $this -- references the current node (inside each, map, filter, search)

Variable Assignment

# Multi-statement with semicolons
cat data.json | dasel -i json '$active = users.filter(active == true); $active.map(name)'

Conditionals

echo '{"count": 7}' | dasel -i json 'if(count > 5) { "many" } else { "few" }'

v3 Breaking Changes from v2

  • put and delete subcommands removed; use inline assignment with --root
  • -f/--file flag removed; input always comes from stdin via pipe
  • Query/selector syntax completely revamped; v2 syntax is NOT compatible with v3
  • CLI framework changed from Cobra to Kong
  • Go module path changed to github.com/tomwright/dasel/v3

Detailed References

Sources

  1. dasel README: https://raw.githubusercontent.com/TomWright/dasel/master/README.md (fetched 2026-02-19)
  2. dasel docs: https://daseldocs.tomwright.me (fetched 2026-02-19)
  3. Query syntax: https://daseldocs.tomwright.me/syntax/query-syntax.md (fetched 2026-02-19)
  4. Functions index: https://daseldocs.tomwright.me/functions (fetched 2026-02-19)
  5. CHANGELOG: https://raw.githubusercontent.com/TomWright/dasel/master/CHANGELOG.md (fetched 2026-02-19)
  6. Releases: https://github.com/TomWright/dasel/releases (fetched 2026-02-19)
  7. Source code analysis: execution/func.go, internal/cli/query.go, internal/cli/run.go, internal/cli/config.go, execution/execute_binary.go, execution/execute_unary.go (analyzed 2026-02-19)
  8. Fact-check: FACT_CHECK_REPORT.md (2026-02-23)