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

Key Functions Quick Reference

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

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

• Selectors and Syntax -- dot notation, arrays, recursive descent, object construction, variables, conditionals, comparison operators
• Functions Reference -- complete function signatures, descriptions, and examples
• Format-Specific Patterns -- JSON, YAML, TOML, XML, CSV, HCL, INI patterns and conversion caveats

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)