NAME

JQ::Lite - A lightweight jq-like JSON query engine in Perl

VERSION

Version 1.27

SYNOPSIS

use JQ::Lite;

my $jq = JQ::Lite->new;
my @results = $jq->run_query($json_text, '.users[].name');

for my $r (@results) {
    print encode_json($r), "\n";
}

DESCRIPTION

JQ::Lite is a lightweight, pure-Perl JSON query engine inspired by the jq command-line tool.

It allows you to extract, traverse, and filter JSON data using a simplified jq-like syntax — entirely within Perl, with no external binaries or XS modules.

FEATURES

• Pure Perl (no XS, no external binaries required)

• Dot notation traversal (e.g. .users[].name)

• Optional key access using '?' (e.g. .nickname?)

• Array indexing and flattening (.users[0], .users[])

• Boolean filters via select(...) with ==, !=, <, >, and, or

• Pipe-style query chaining using | operator

• Built-in functions: length, keys, keys_unsorted, values, first, last, reverse, sort, sort_desc, sort_by, min_by, max_by, unique, unique_by, has, contains, test, any, all, not, group_by, group_count, join, split, explode, implode, count, empty, type, nth, del, delpaths, compact, upper, lower, titlecase, abs, ceil, floor, trim, ltrimstr, rtrimstr, substr, slice, startswith, endswith, add, sum, sum_by, avg_by, median_by, product, min, max, avg, median, mode, percentile, variance, stddev, drop, tail, chunks, range, enumerate, transpose, flatten_all, flatten_depth, clamp, tostring, tojson, fromjson, to_number, pick, merge_objects, to_entries, from_entries, with_entries, map_values, walk, paths, leaf_paths, getpath, setpath, index, rindex, indices, arrays, objects, scalars

• Supports map(...), map_values(...), walk(...), limit(n), drop(n), tail(n), chunks(n), range(...), and enumerate() style transformations

• Interactive mode for exploring queries line-by-line

• Command-line interface: jq-lite (compatible with stdin or file)

• Decoder selection via --use (JSON::PP, JSON::XS, etc.)

• Debug output via --debug

• List all functions with --help-functions

CONSTRUCTOR

new

my $jq = JQ::Lite->new;

Creates a new instance. Options may be added in future versions.

METHODS

run_query

my @results = $jq->run_query($json_text, $query);

Runs a jq-like query against the given JSON string. Returns a list of matched results. Each result is a Perl scalar (string, number, arrayref, hashref, etc.) depending on the query.

SUPPORTED SYNTAX

• .key.subkey

• .array[0] (index access)

• .array[] (flattening arrays)

• .key? (optional key access)

• select(.key > 1 and .key2 == "foo") (boolean filters)

• group_by(.field) (group array items by key)

• reduce expr as $var (init; update) (accumulate values with lexical bindings)

• foreach expr as $var (init; update [; extract]) (stream results while folding values)

• if CONDITION then FILTER [elif CONDITION then FILTER ...] [else FILTER] end (conditional branching)

  Evaluates jq-style conditional expressions. Conditions are treated as filters executed against the current input; the first branch whose condition produces a truthy result has its filter evaluated and emitted. Optional elif clauses cascade additional tests, and the optional else filter runs only when no prior branch matched. When no else clause is supplied and every condition is falsey the expression yields no output.

  Example:

  if .score >= 90 then "A"
  elif .score >= 80 then "B"
  else "C"
  end

• group_count(.field) (tally items by key)

• sum_by(.field) (sum numeric values projected from each array item)

• avg_by(.field) (average numeric values projected from each array item)

• median_by(.field) (median of numeric values projected from each array item)

• percentile(p) (return the requested percentile for numeric array values)

• min_by(.field) / max_by(.field) (select array element with smallest/largest projected value)

• sort_desc()

  Sort array elements in descending order using smart numeric/string comparison.

  Example:

  .scores | sort_desc

  Returns:

  [100, 75, 42, 12]

• sort_by(.key) (sort array of objects by key)

• unique_by(.key) (remove duplicates based on a projected key)

• .key | count (count items or fields)

• .[] | select(...) | count (combine flattening + filter + count)

• .array | map(.field) | join(", ")

  Concatenates array elements with a custom separator string. Example:

  .users | map(.name) | join(", ")

  Results in:

  "Alice, Bob, Carol"

• split(separator)

  Split string values (and arrays of strings) using a literal separator. Example:

  .users[0].name | split("")

  Results in:

  ["A", "l", "i", "c", "e"]

• explode()

  Convert strings into arrays of Unicode code points. When applied to arrays the conversion happens element-wise, while non-string values (including hashes) are passed through untouched. This mirrors jq's explode helper and pairs with implode for round-trip transformations.

  Example:

  .title | explode

  Returns:

  [67, 79, 68, 69]

• implode()

  Perform the inverse of explode by turning arrays of Unicode code points back into strings. Nested arrays are processed recursively so pipelines like explode | implode work over heterogeneous structures. Non-array inputs pass through unchanged.

  Example:

  .codes | implode

  Returns:

  "CODE"

• keys_unsorted()

  Returns the keys of an object without sorting them, mirroring jq's keys_unsorted helper. Arrays yield their zero-based indices, while non-object/array inputs return undef to match the behaviour of keys.

  Example:

  .profile | keys_unsorted

• values()

  Returns all values of a hash as an array. Example:

  .profile | values

• paths()

  Enumerates every path within the current value, mirroring jq's paths helper. Each path is emitted as an array of keys and/or indices leading to objects, arrays, and their nested scalars. Scalars (including booleans and null) yield a single empty path, while empty arrays and objects contribute only their immediate location.

  Example:

  .user | paths

  Returns:

  [ ["name"], ["tags"], ["tags",0], ["tags",1], ["active"] ]

• leaf_paths()

  Enumerates only the paths that terminate in non-container values, mirroring jq's leaf_paths helper. This is equivalent to paths(scalars) in jq.

  Example:

  .user | leaf_paths

  Returns:

  [ ["name"], ["tags",0], ["tags",1], ["active"] ]

• getpath(path)

  Retrieves the value referenced by the supplied path array (or filter producing path arrays), mirroring jq's getpath/1. Literal JSON arrays can be passed directly while expressions such as paths() are evaluated against the current input to collect candidate paths. When multiple paths are returned the helper yields an array of values in the same order.

  Examples:

  .profile | getpath(["name"])          # => "Alice"
  .profile | getpath(["emails", 1])     # => "alice.work\@example.com"
  .profile | getpath(paths())

• setpath(path; value)

  Sets or creates a value at the supplied path, following jq's setpath/2 semantics. The first argument may be a literal JSON array or any filter that emits path arrays. The second argument can be a literal (including JSON objects/arrays) or another filter evaluated against the current input. Nested hashes/arrays are automatically created as needed, and the original input is never mutated.

  Examples:

  .settings | setpath(["flags", "beta"]; true)
  .user     | setpath(["profile", "full_name"]; .name)

• pick(key1, key2, ...)

  Builds a new object containing only the supplied keys. When applied to arrays of objects, each element is reduced to the requested subset while non-object values pass through unchanged.

  Example:

  .users | pick("name", "email")

  Returns:

  [ { "name": "Alice", "email": "alice\@example.com" },
    { "name": "Bob" } ]

• merge_objects()

  Merges arrays of objects into a single hash reference using last-write-wins semantics. Non-object values within the array are ignored. When no objects are found, an empty hash reference is returned. Applying the helper directly to an object returns a shallow copy of that object.

  Example:

  .items | merge_objects()

  Returns:

  { "name": "Widget", "value": 2, "active": true }

• to_entries()

  Converts objects (and arrays) into an array of entry hashes, each consisting of key and value fields in the jq style. Array entries use zero-based index values for the key so they can be transformed uniformly.

  Example:

  .profile | to_entries
  .tags    | to_entries

• from_entries()

  Performs the inverse of to_entries. Accepts arrays containing { key = ..., value => ... }> hashes or [key, value] tuples and rebuilds a hash from them. Later entries overwrite earlier ones when duplicate keys are encountered.

  Example:

  .pairs | from_entries

• with_entries(filter)

  Transforms objects by mapping over their entries with the supplied filter, mirroring jq's with_entries. Each entry is exposed as a { key, value } hash to the filter, and any entries filtered out are dropped prior to reconstruction.

  Example:

  .profile | with_entries(select(.key != "password"))

• map_values(filter)

  Applies the supplied filter to every value within an object, mirroring jq's map_values. When the filter returns no results for a key the entry is removed, allowing constructs such as map_values(select(. 0))> to prune falsy values. Arrays are processed element-wise, so arrays of objects can be transformed in a single step.

  Example:

  .profile | map_values(tostring)

  Returns:

  { "name": "Alice", "age": "42" }

• walk(filter)

  Recursively traverses arrays and objects, applying the supplied filter to each value after its children have been transformed, matching jq's walk/1 behaviour. Arrays and hashes are rebuilt so nested values can be updated in a single pass, while scalars pass directly to the filter.

  Example:

  .profile | walk(upper)

  Returns:

  { "name": "ALICE", "note": "TEAM LEAD" }

• recurse([filter])

  Performs a depth-first traversal mirroring jq's recurse. Each invocation emits the current value and then evaluates either the optional child filter or, when omitted, the object's values and array elements. This makes it easy to walk arbitrary tree structures:

  Example:

  .users[0] | recurse(.children[]?) | .name

  Returns:

  "Alice"
  "Bob"
  "Carol"

• empty()

  Discards all output. Compatible with jq. Useful when only side effects or filtering is needed without output.

  Example:

  .users[] | select(.age > 25) | empty

• .[] as alias for flattening top-level arrays

• transpose()

  Pivots an array of arrays from row-oriented to column-oriented form. When rows have different lengths, the result truncates to the shortest row so that every column contains the same number of elements.

  Example:

  [[1, 2, 3], [4, 5, 6]] | transpose

  Returns:

  [[1, 4], [2, 5], [3, 6]]

• flatten_all()

  Recursively flattens nested arrays into a single-level array while preserving non-array values.

  Example:

  [[1, 2], [3, [4]]] | flatten_all

  Returns:

  [1, 2, 3, 4]

• flatten_depth(n)

  Flattens nested arrays up to n levels deep while leaving deeper nesting intact.

  Example:

  [[1, [2]], [3, [4]]] | flatten_depth(1)

  Returns:

  [1, [2], 3, [4]]

• arrays

  Emits its input only when the value is an array reference, mirroring jq's arrays filter. Scalars and objects yield no output, making it convenient to select array inputs prior to additional processing.

  Example:

  .items[] | arrays

  Returns only the array entries from .items.

• objects

  Emits its input only when the value is a hash reference, mirroring jq's objects filter. Scalars and arrays yield no output, letting you isolate objects inside heterogeneous streams.

  Example:

  .items[] | objects

  Returns only the object entries from .items.

• scalars

  Emits its input only when the value is a scalar (including strings, numbers, booleans, or null/undef), mirroring jq's scalars helper. Arrays and objects yield no output, making it easy to focus on terminal values within mixed streams.

  Example:

  .items[] | scalars

  Returns only the scalar entries from .items.

• type()

  Returns the type of the value as a string: "string", "number", "boolean", "array", "object", or "null".

  Example:

  .name | type     # => "string"
  .tags | type     # => "array"
  .profile | type  # => "object"

• lhs // rhs

  Implements jq's alternative operator. The left-hand side is returned when it produces a defined value (including false or empty arrays); otherwise the right-hand expression is evaluated as a fallback.

  Example:

  .users[] | (.nickname // .name)

  Returns the nickname when present, otherwise the name field.

• default(value)

  Provides a convenience helper to replace undefined or null pipeline values with a literal fallback.

  Example:

  .nickname | default("unknown")

  Ensures the string "unknown" is emitted when .nickname is missing or null.

• nth(n)

  Returns the nth element (zero-based) from an array.

  Example:

  .users | nth(0)   # first user
  .users | nth(2)   # third user

• del(key)

  Deletes a specified key from a hash object and returns a new hash without that key.

  Example:

  .profile | del("password")

  If the key does not exist, returns the original hash unchanged.

  If applied to a non-hash object, returns the object unchanged.

• delpaths(paths)

  Removes multiple keys or indices identified by the supplied paths expression. The expression is evaluated against the current input (for example by using paths() or other jq-lite helpers) and should yield an array of path arrays, mirroring jq's delpaths/1 behaviour.

  Example:

  .profile | delpaths([["password"], ["tokens", 0]])

  Paths can be generated dynamically using helpers such as paths() before being passed to delpaths. When a referenced path is missing it is ignored. Providing an empty path ([] ) removes the entire input value, yielding null.

• compact()

  Removes undef and null values from an array.

  Example:

  .data | compact()

  Before: [1, null, 2, null, 3]

  After: [1, 2, 3]

• upper()

  Converts strings to uppercase. When applied to arrays, each scalar element is uppercased recursively, leaving nested hashes or booleans untouched.

  Example:

  .title | upper      # => "HELLO WORLD"
  .tags  | upper      # => ["PERL", "JSON"]

• titlecase()

  Converts strings to title case (first letter of each word uppercase). When applied to arrays, each scalar element is transformed recursively, leaving nested hashes or booleans untouched.

  Example:

  .title | titlecase   # => "Hello World"
  .tags  | titlecase   # => ["Perl", "Json"]

• lower()

  Converts strings to lowercase. When applied to arrays, each scalar element is lowercased recursively, leaving nested hashes or booleans untouched.

  Example:

  .title | lower      # => "hello world"
  .tags  | lower      # => ["perl", "json"]

• has(key)

  Checks whether the current value exposes the supplied key or index.

  * For hashes, returns true when the key is present. * For arrays, returns true when the zero-based index exists.

  Example:

  .meta  | has("version")   # => true
  .items | has(2)            # => true when at least 3 elements exist

• contains(value)

  Checks whether the current value includes the supplied fragment.

  * For strings, returns true when the substring exists. * For arrays, returns true if any element equals the supplied value. * For hashes, returns true when the key is present.

  Example:

  .title | contains("perl")     # => true
  .tags  | contains("json")     # => true
  .meta  | contains("lang")     # => true

• test(pattern[, flags])

  Evaluates whether the current string input matches a regular expression. The pattern is interpreted as a Perl-compatible regex, and optional flag strings support the common jq modifiers i, m, s, and x.

  * Scalars are coerced to strings before matching (booleans become "true" or "false"). * Arrays are processed element-wise, returning arrays of JSON booleans. * Non-string container values that cannot be coerced yield false.

  Examples:

  .title | test("^Hello")           # => true
  .title | test("world")            # => false (case-sensitive)
  .title | test("world"; "i")      # => true (case-insensitive)
  .tags  | test("^p")               # => [true, false, false]

• all([filter])

  Evaluates whether every element (optionally projected through filter) is truthy, mirroring jq's all/1 helper.

  • For arrays without a filter, returns true when every element is truthy (empty arrays yield true).

  • For arrays with a filter, applies the filter to each element and requires every produced value to be truthy.

  • When the current input is a scalar, falls back to checking the value's truthiness (or the filter's results when supplied).

  Examples:

  .flags | all            # => true when every element is truthy (empty => true)
  .users | all(.active)   # => true when every user is active

• any([filter])

  Returns true when at least one value in the input is truthy. When a filter is provided, it is evaluated against each array element (or the current value when not operating on an array) and the truthiness of the filter's results is used.

  * For arrays without a filter, returns true if any element is truthy. * For arrays with a filter, returns true when the filter yields a truthy value for any element. * For scalars, hashes, and other values, evaluates the value (or filter results) directly.

  Example:

  .flags | any            # => true when any element is truthy
  .users | any(.active)   # => true when any user is active

• not

  Performs logical negation using jq's truthiness rules. Returns true when the current input is falsy (e.g. false, null, empty string, empty array, or empty object) and false otherwise. Arrays and objects are considered truthy when they contain at least one element or key, respectively.

  Examples:

  true  | not   # => false
  []    | not   # => true
  .ok   | not   # => negates the truthiness of .ok

• unique_by(".key")

  Removes duplicate objects (or values) from an array by projecting each entry to the supplied key path and keeping only the first occurrence of each signature. Use . to deduplicate by the entire value.

  Example:

  .users | unique_by(.name)      # => keeps first record for each name
  .tags  | unique_by(.)          # => removes duplicate scalars

• startswith("prefix")

  Returns true if the current string (or each string inside an array) begins with the supplied prefix. Non-string values yield false.

  Example:

  .title | startswith("Hello")   # => true
  .tags  | startswith("j")       # => [false, true, false]

• endswith("suffix")

  Returns true if the current string (or each string inside an array) ends with the supplied suffix. Non-string values yield false.

  Example:

  .title | endswith("World")     # => true
  .tags  | endswith("n")         # => [false, true, false]

• substr(start[, length])

  Extracts a substring from the current string using zero-based indexing. When applied to arrays, each scalar element receives the same slicing arguments recursively.

  Examples:

  .title | substr(0, 5)       # => "Hello"
  .tags  | substr(-3)         # => ["erl", "SON"]

• slice(start[, length])

  Returns a portion of the current array using zero-based indexing. Negative start values count from the end of the array. When length is omitted, the slice continues through the final element. Non-array inputs pass through unchanged so pipelines can mix scalar and array values safely.

  Examples:

  .users | slice(0, 2)        # => first two users
  .users | slice(-2)          # => last two users

• tail(n)

  Returns the final n elements of the current array. When n is zero the result is an empty array, and when n exceeds the array length the entire array is returned unchanged. Non-array inputs pass through untouched so the helper composes cleanly inside pipelines that also yield scalars or objects.

  Examples:

  .users | tail(2)            # => last two users
  .users | tail(10)           # => full array when shorter than 10

• range(start; end[, step])

  Emits a numeric sequence that begins at start (default 0) and advances by step (default 1) until reaching but not including end. When the step is negative the helper counts downward and stops once the value is less than or equal to the exclusive bound. Non-numeric arguments result in the input being passed through unchanged so pipelines remain resilient.

  Examples:

  null | range(5)           # => 0,1,2,3,4
  null | range(2; 6; 2)     # => 2,4
  null | range(10; 2; -4)   # => 10,6

• enumerate()

  Converts arrays into an array of objects pairing each element with its zero-based index. Each object contains two keys: index for the position and value for the original element. Non-array inputs are returned unchanged so the helper composes inside pipelines that may yield scalars or hashes.

  Examples:

  .users | enumerate()          # => [{"index":0,"value":...}, ...]
  .numbers | enumerate() | map(.index)

• index(value)

  Returns the zero-based index of the first occurrence of the supplied value. When the current result is an array, deep comparisons are used so nested structures (hashes, arrays, booleans) work as expected. When the current value is a string, the function returns the position of the substring, or null when not found.

  Example:

  .users | index("Alice")     # => 0
  .tags  | index("json")      # => 1

• rindex(value)

  Returns the zero-based index of the final occurrence of the supplied value. Array inputs are scanned from the end using deep comparisons, while string inputs return the position of the last matching substring (or null when not found).

  Example:

  .users | rindex("Alice")    # => 3
  .tags  | rindex("perl")     # => 2
  "banana" | rindex("an")    # => 3

• indices(value)

  Returns every zero-based index where the supplied value appears. For arrays, deep comparisons are performed against each element and the matching indexes are collected into an array. For strings, the helper searches for literal substring matches (including overlapping ones) and emits each starting position. When the fragment is empty, positions for every character boundary are returned to mirror jq's behaviour.

  Example:

  .users | indices("Alice")     # => [0, 3]
  "banana" | indices("an")      # => [1, 3]
  "perl"   | indices("")        # => [0, 1, 2, 3, 4]

• abs()

  Returns absolute values for numbers. Scalars are converted directly, while arrays are processed element-by-element with non-numeric entries preserved.

  Example:

  .temperature | abs      # => 12
  .deltas      | abs      # => [3, 4, 5, "n/a"]

• ceil()

  Rounds numbers up to the nearest integer. Scalars and array elements that look like numbers are rounded upward, while other values pass through unchanged.

  Example:

  .price   | ceil     # => 20
  .changes | ceil     # => [2, -1, "n/a"]

• floor()

  Rounds numbers down to the nearest integer. Scalars and array elements that look like numbers are rounded downward, leaving non-numeric values untouched.

  Example:

  .price   | floor    # => 19
  .changes | floor    # => [1, -2, "n/a"]

• round()

  Rounds numbers to the nearest integer using standard rounding (half up for positive values, half down for negatives). Scalars and array elements that look like numbers are adjusted, while other values pass through unchanged.

  Example:

  .price   | round    # => 19
  .changes | round    # => [1, -2, "n/a"]

• clamp(min, max)

  Constrains numeric values within the supplied inclusive range. Scalars and array elements that look like numbers are coerced into numeric context and clamped between the provided minimum and maximum. When a bound is omitted or non-numeric, it is treated as unbounded on that side. Non-numeric values pass through unchanged so pipelines remain lossless.

  Example:

  .score  | clamp(0, 100)       # => 87
  .deltas | clamp(-5, 5)        # => [-5, 2, 5, "n/a"]

• tostring()

  Converts the current value into a JSON string representation. Scalars are stringified directly, booleans become "true"/"false", and undefined values are rendered as "null". Arrays and objects are encoded to their JSON text form so the output matches jq's behavior when applied to structured data.

  Example:

  .score   | tostring   # => "42"
  .profile | tostring   # => "{\"name\":\"Alice\"}"

• tojson()

  Encodes the current value as JSON text regardless of its original type, mirroring jq's tojson. Scalars, booleans, nulls, arrays, and objects all produce a JSON string, allowing raw string inputs to be re-escaped safely for embedding or subsequent decoding.

  Example:

  .score   | tojson   # => "42"
  .name    | tojson   # => "\"Alice\""
  .profile | tojson   # => "{\"name\":\"Alice\"}"

• fromjson()

  Parses JSON text back into native Perl data structures. Plain strings are decoded directly, while arrays are processed element-by-element to mirror jq's convenient broadcasting behaviour. Invalid JSON inputs are passed through unchanged so pipelines remain lossless.

  Example:

  .raw   | fromjson   # => {"name":"Bob"}
  .lines | fromjson   # => [1, true, null]

• to_number()

  Coerces values that look like numbers into actual numeric scalars. Strings are converted with Perl's numeric semantics, booleans become 1 or 0, and arrays are processed element-by-element. Non-numeric strings, objects, and other references are returned unchanged so pipelines remain lossless.

  Example:

  .score    | to_number   # => 42
  .strings  | to_number   # => [10, "n/a", 3.5]

• trim()

  Removes leading and trailing whitespace from strings. Arrays are processed recursively, while hashes and other references are left untouched.

  Example:

  .title | trim          # => "Hello World"
  .tags  | trim          # => ["perl", "json"]

• ltrimstr("prefix")

  Removes prefix from the start of strings when present. Arrays are processed recursively so nested string values receive the same treatment. Inputs that do not begin with the supplied prefix are returned unchanged.

  Example:

  .title | ltrimstr("Hello ")  # => "World"
  .tags  | ltrimstr("#")       # => ["perl", "json"]

• rtrimstr("suffix")

  Removes suffix from the end of strings when present. Arrays are processed recursively so nested string values are handled consistently. Inputs that do not end with the supplied suffix are returned unchanged.

  Example:

  .title | rtrimstr(" World")  # => "Hello"
  .tags  | rtrimstr("ing")     # => ["perl", "json"]

COMMAND LINE USAGE

jq-lite is a CLI wrapper for this module.

cat data.json | jq-lite '.users[].name'
jq-lite '.users[] | select(.age > 25)' data.json
jq-lite -r '.users[].name' data.json
jq-lite '.[] | select(.active == true) | .name' data.json
jq-lite '.users[] | select(.age > 25) | count' data.json
jq-lite '.users | map(.name) | join(", ")'
jq-lite '.users[] | select(.age > 25) | empty'
jq-lite '.profile | values'

Interactive Mode

Omit the query to enter interactive mode:

jq-lite data.json

You can then type queries line-by-line against the same JSON input.

Decoder Selection and Debug

jq-lite --use JSON::PP --debug '.users[0].name' data.json

Show Supported Functions

jq-lite --help-functions

Displays all built-in functions and their descriptions.

REQUIREMENTS

Uses only core modules:

• JSON::PP

Optional: JSON::XS, Cpanel::JSON::XS, JSON::MaybeXS

SEE ALSO

JSON::PP, jq

AUTHOR

Kawamura Shingo <pannakoota1@gmail.com>

LICENSE

Same as Perl itself.

cpanm JQ::Lite

perl -MCPAN -e shell
install JQ::Lite