dasel（dasel 搜索）

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:

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 -f flag for data files in v3. Always use stdin (< file or cat 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

Key functions

For full function signatures and examples, see references/functions.md.

Reference files

Tips

• Always use --root when modifying data and wanting the full document back.
• Use ; to write multi-statement queries for clarity.
• $root is the stdin document; $this is the current element inside functions.
• For in-place file edits, always redirect to a .tmp file first, then mv.
• The ternary operator (?:) is not yet implemented — use if/else form instead.
• branch is unstable — requires --unstable flag.