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

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

dasel README: https://raw.githubusercontent.com/TomWright/dasel/master/README.md (fetched 2026-02-19)
dasel docs: https://daseldocs.tomwright.me (fetched 2026-02-19)
Query syntax: https://daseldocs.tomwright.me/syntax/query-syntax.md (fetched 2026-02-19)
Functions index: https://daseldocs.tomwright.me/functions (fetched 2026-02-19)
CHANGELOG: https://raw.githubusercontent.com/TomWright/dasel/master/CHANGELOG.md (fetched 2026-02-19)
Releases: https://github.com/TomWright/dasel/releases (fetched 2026-02-19)
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)
Fact-check: FACT_CHECK_REPORT.md (2026-02-23)