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dasel
GitHub使用 dasel CLI 查询、修改和转换结构化数据（JSON/YAML/TOML等）。适用于读写文件、编写查询表达式、过滤映射数据、原地编辑配置及管道处理。
Trigger Scenarios
用户需要使用 dasel 读取、写入或转换数据文件
用户需要编写 dasel 查询表达式以过滤、映射或转换数据
用户希望在命令行中就地编辑配置文件
用户在 shell 脚本中通过管道使用 dasel
用户询问 dasel 语法、函数或 CLI 标志
Install
npx skills add NeverSight/learn-skills.dev --skill dasel -g -y
SKILL.md
Frontmatter
{
"name": "dasel",
"description": "Use dasel v3 CLI to query, modify, and transform structured data (JSON, YAML, TOML, XML, CSV, HCL, INI). Load this skill whenever the user wants to: read\/write\/convert data files with dasel, write dasel query expressions, filter\/map\/transform structured data on the command line, edit config files in place using dasel, pipe data through dasel in shell scripts, or asks about dasel syntax, functions, or CLI flags. Even if they just say \"use dasel to...\" or \"dasel query for...\", load this skill."
}
Dasel v3
Dasel (Data-Select) is a CLI tool for querying, modifying, and converting structured data files using a consistent query syntax across formats.
Docs are bundled in
references/. Read them when you need deeper detail on a topic.
CLI basics
# Read from stdin, specify input format
echo '{"name":"Tom"}' | dasel -i json 'name'
# => "Tom"
# Read from a file via stdin redirection
dasel -i yaml 'database.host' < config.yaml
# Convert formats: read JSON, output YAML
cat data.json | dasel -i json -o yaml
# Output the whole document (needed when modifying)
echo '{"a":1}' | dasel -i json --root 'a = 2'
# => {"a": 2}
Key flags:
| Flag | Short | Purpose |
|---|---|---|
--in FORMAT |
-i |
Input format (json, yaml, toml, xml, csv, hcl, ini) |
--out FORMAT |
-o |
Output format |
--root |
Output the full document, not just the selected value | |
--var name=fmt:file:path |
Pass a file as a named variable | |
--read-flag key=val |
Parser-specific read options | |
--write-flag key=val |
Parser-specific write options | |
--config PATH |
-c |
Path to dasel config file (default: ~/dasel.yaml) |
--unstable |
Enable unstable/experimental features |
Query syntax
Queries are dot-chained accessors and function calls, terminated with ; when using multiple statements.
# Access nested fields
user.address.city
# Array index (zero-based)
users[0].name
# Range slice
users[0:4]
# Assign (modifies the value in the document)
user.name = "Alice"
# Variables - $root is stdin, $this is current element
$root.users.filter(active == true).map(name)
Multi-statement queries (use ; to separate, last statement is the output):
$active = $root.users.filter(active == true);
$active.map(name)
Environment variables
GREETING=hello NAME=tom dasel '$GREETING + " " + $NAME'
# => "hello tom"
Common patterns
Read a value
echo '{"foo":{"bar":"baz"}}' | dasel -i json 'foo.bar'
# => "baz"
Modify a value (output full document)
echo '{"foo":"old"}' | dasel -i json --root 'foo = "new"'
# => {"foo": "new"}
Edit a file in place
dasel -i yaml --root 'server.port = 9090' < config.yaml > config.yaml.tmp \
&& mv config.yaml.tmp config.yaml
Note: there is no
-fflag for data files in v3. Always use stdin (< fileorcat file |). Note: always go via a temp file — bash truncates the target before dasel reads it.
Filter an array
echo '{"users":[{"name":"Alice","active":true},{"name":"Bob","active":false}]}' \
| dasel -i json 'users.filter(active == true).map(name)'
# => ["Alice"]
Map / transform
echo '[1,2,3]' | dasel -i json 'map($this * 2)'
# => [2, 4, 6]
Modify elements in place with each
echo '[1,2,3]' | dasel -i json 'each($this = $this + 1)'
# => [2, 3, 4]
Default / coalesce
# Fall back to a default if path missing
dasel -f config.yaml 'server.timeout ?? 30'
Conditional
dasel -f data.json 'if(count > 5) { "many" } else { "few" }'
Recursive descent — find all values by key
# All values with key "name" at any depth
dasel -f data.json '..name'
# All values at any depth
dasel -f data.json '..*'
Predicate-based deep search
dasel -f data.json 'search(has("id") && has("name"))'
Format conversion
cat file.json | dasel -i json -o yaml
cat file.yaml | dasel -i yaml -o toml
Build a new object
echo '{"first":"Tom","last":"Wright"}' \
| dasel -i json '{"fullName": first + " " + last}'
Spread operator
# Merge objects
echo '{"a":1}' | dasel -i json '{$this..., "b": 2}'
# => {"a":1,"b":2}
# Append to array
echo '[1,2,3]' | dasel -i json '[$this..., 4, 5]'
# => [1,2,3,4,5]
Supported formats
| Format | Read | Write | Notes |
|---|---|---|---|
| json | ✓ | ✓ | |
| yaml | ✓ | ✓ | |
| xml | ✓ | ✓ | See --read-flag xml-mode=structured |
| csv | ✓ | ✓ | All values as strings; --read-flag csv-delimiter=; |
| hcl | ✓ | ✓ | --read-flag hcl-block-format=array |
| toml | ✓ | ✓ | Generally working; unsorted maps |
| ini | ✓ | ✓ | Basic sections + key values only |
Key functions
| Function | Description | Example |
|---|---|---|
filter(pred) |
Filter array by predicate | arr.filter($this > 1) |
map(expr) |
Transform each element | arr.map($this * 2) |
each(expr) |
Iterate and modify in place | arr.each($this = $this+1) |
search(pred) |
Recursive predicate search | search(has("key")) |
has(key) |
Check key/index exists | has("name") |
len(x) |
Length of array/string | len($root.items) |
keys(obj) |
Keys of a map | keys($root.config) |
add(a,b) |
Add / concatenate | add(1, 2) |
join(arr, sep) |
Join array to string | join(tags, ",") |
replace(str,old,new) |
String replace | replace(name,"_"," ") |
sortBy(key) |
Sort array of objects | users.sortBy(name) |
reverse(arr) |
Reverse array | reverse(items) |
min(arr) / max(arr) |
Min/max of numbers | min(scores) |
sum(arr) |
Sum numbers | sum(prices) |
toString(x) |
Convert to string | toString(id) |
toInt(x) |
Convert to int | toInt(count) |
typeOf(x) |
Type name | typeOf(value) |
parse(fmt, str) |
Parse a string as a format | parse("json", raw) |
readFile(path) |
Read a file | readFile("x.json") |
base64e(str) |
Base64 encode | base64e(token) |
base64d(str) |
Base64 decode | base64d(encoded) |
For full function signatures and examples, see
references/functions.md.
Reference files
| File | When to read |
|---|---|
references/syntax.md |
Deep dive: types, arrays, objects, conditionals, spread, coalesce, branches, regex, recursive descent |
references/functions.md |
All function signatures with examples |
references/input-output.md |
Stdin/stdout, file editing, variables, format flags |
Tips
- Always use
--rootwhen modifying data and wanting the full document back. - Use
;to write multi-statement queries for clarity. $rootis the stdin document;$thisis the current element inside functions.- For in-place file edits, always redirect to a
.tmpfile first, thenmv. - The ternary operator (
? :) is not yet implemented — useif/elseform instead. branchis unstable — requires--unstableflag.
Version History
- e0220ca Current 2026-07-05 22:10
