Updating docs for v4.19.1 release

operators/add.md

@@ -9,28 +9,11 @@ Add behaves differently according to the type of the LHS:
 Use `+=` as a relative append assign for things like increment. Note that `.a += .x` is equivalent to running `.a = .a + .x`.
 
 
-## Concatenate and assign arrays
-Given a sample.yml file of:
-```yaml
-a:
-  val: thing
-  b:
-    - cat
-    - dog
-```
-then
-```bash
-yq '.a.b += ["cow"]' sample.yml
-```
-will output
-```yaml
-a:
-  val: thing
-  b:
-    - cat
-    - dog
-    - cow
-```
+{% hint style="warning" %}
+Note that versions prior to 4.18 require the 'eval/e' command to be specified. 
+
+`yq e <exp> <file>`
+{% endhint %}
 
 ## Concatenate arrays
 Given a sample.yml file of:
@@ -54,6 +37,28 @@ will output
 - 4
 ```
 
+## Concatenate to existing array
+Note that the styling of `a` is kept.
+
+Given a sample.yml file of:
+```yaml
+a: [1,2]
+b:
+  - 3
+  - 4
+```
+then
+```bash
+yq '.a += .b' sample.yml
+```
+will output
+```yaml
+a: [1, 2, 3, 4]
+b:
+  - 3
+  - 4
+```
+
 ## Concatenate null to array
 Given a sample.yml file of:
 ```yaml
@@ -71,6 +76,22 @@ will output
 - 2
 ```
 
+## Append to existing array
+Note that the styling is copied from existing array elements
+
+Given a sample.yml file of:
+```yaml
+a: ['dog']
+```
+then
+```bash
+yq '.a += "cat"' sample.yml
+```
+will output
+```yaml
+a: ['dog', 'cat']
+```
+
 ## Add new object to array
 Given a sample.yml file of:
 ```yaml
@@ -87,76 +108,6 @@ will output
 - cat: meow
 ```
 
-## Add string to array
-Given a sample.yml file of:
-```yaml
-a:
-  - 1
-  - 2
-```
-then
-```bash
-yq '.a + "hello"' sample.yml
-```
-will output
-```yaml
-- 1
-- 2
-- hello
-```
-
-## Append to array
-Given a sample.yml file of:
-```yaml
-a:
-  - 1
-  - 2
-b:
-  - 3
-  - 4
-```
-then
-```bash
-yq '.a = .a + .b' sample.yml
-```
-will output
-```yaml
-a:
-  - 1
-  - 2
-  - 3
-  - 4
-b:
-  - 3
-  - 4
-```
-
-## Append another array using +=
-Given a sample.yml file of:
-```yaml
-a:
-  - 1
-  - 2
-b:
-  - 3
-  - 4
-```
-then
-```bash
-yq '.a += .b' sample.yml
-```
-will output
-```yaml
-a:
-  - 1
-  - 2
-  - 3
-  - 4
-b:
-  - 3
-  - 4
-```
-
 ## Relative append
 Given a sample.yml file of:
 ```yaml
@@ -195,7 +146,7 @@ b: meow
 ```
 then
 ```bash
-yq '.a = .a + .b' sample.yml
+yq '.a += .b' sample.yml
 ```
 will output
 ```yaml

operators/alternative-default-value.md

@@ -2,6 +2,12 @@
 
 This operator is used to provide alternative (or default) values when a particular expression is either null or false.
 
+{% hint style="warning" %}
+Note that versions prior to 4.18 require the 'eval/e' command to be specified. 
+
+`yq e <exp> <file>`
+{% endhint %}
+
 ## LHS is defined
 Given a sample.yml file of:
 ```yaml

operators/anchor-and-alias-operators.md

@@ -5,6 +5,12 @@ Use the `alias` and `anchor` operators to read and write yaml aliases and anchor
 `yq` supports merge aliases (like `<<: *blah`) however this is no longer in the standard yaml spec (1.2) and so `yq` will automatically add the `!!merge` tag to these nodes as it is effectively a custom tag.
 
 
+{% hint style="warning" %}
+Note that versions prior to 4.18 require the 'eval/e' command to be specified.&#x20;
+
+`yq e <exp> <file>`
+{% endhint %}
+
 ## Merge one map
 see https://yaml.org/type/merge.html
 

operators/assign-update.md

@@ -7,6 +7,12 @@ Which will assign the LHS node values to the RHS node values. The RHS expression
 
 ### relative form: `|=`
 This will do a similar thing to the plain form, however, the RHS expression is run against _the LHS nodes_. This is useful for updating values based on old values, e.g. increment.
+{% hint style="warning" %}
+Note that versions prior to 4.18 require the 'eval/e' command to be specified. 
+
+`yq e <exp> <file>`
+{% endhint %}
+
 ## Create yaml file
 Running
 ```bash

operators/boolean-operators.md

@@ -10,6 +10,12 @@ The `or` and `and` operators take two parameters and return a boolean result.
 
 These are most commonly used with the `select` operator to filter particular nodes.
 
+{% hint style="warning" %}
+Note that versions prior to 4.18 require the 'eval/e' command to be specified. 
+
+`yq e <exp> <file>`
+{% endhint %}
+
 ## `or` example
 Running
 ```bash

operators/collect-into-array.md

@@ -3,6 +3,12 @@
 This creates an array using the expression between the square brackets.
 
 
+{% hint style="warning" %}
+Note that versions prior to 4.18 require the 'eval/e' command to be specified. 
+
+`yq e <exp> <file>`
+{% endhint %}
+
 ## Collect empty
 Running
 ```bash

operators/comment-operators.md

@@ -10,6 +10,12 @@ This will assign the LHS nodes comments to the expression on the RHS. The RHS is
 ### relative form: `|=` 
 Similar to the plain form, however the RHS evaluates against each matching LHS node! This is useful if you want to set the comments as a relative expression of the node, for instance its value or path.
 
+{% hint style="warning" %}
+Note that versions prior to 4.18 require the 'eval/e' command to be specified. 
+
+`yq e <exp> <file>`
+{% endhint %}
+
 ## Set line comment
 Given a sample.yml file of:
 ```yaml

operators/contains.md

@@ -2,6 +2,12 @@
 
 This returns `true` if the context contains the passed in parameter, and false otherwise.
 
+{% hint style="warning" %}
+Note that versions prior to 4.18 require the 'eval/e' command to be specified. 
+
+`yq e <exp> <file>`
+{% endhint %}
+
 ## Array contains array
 Array is equal or subset of
 

operators/create-collect-into-object.md

@@ -2,6 +2,12 @@
 
 This is used to construct objects (or maps). This can be used against existing yaml, or to create fresh yaml documents.
 
+{% hint style="warning" %}
+Note that versions prior to 4.18 require the 'eval/e' command to be specified. 
+
+`yq e <exp> <file>`
+{% endhint %}
+
 ## Collect empty object
 Running
 ```bash

operators/delete.md

@@ -2,6 +2,12 @@
 
 Deletes matching entries in maps or arrays.
 
+{% hint style="warning" %}
+Note that versions prior to 4.18 require the 'eval/e' command to be specified. 
+
+`yq e <exp> <file>`
+{% endhint %}
+
 ## Delete entry in map
 Given a sample.yml file of:
 ```yaml

operators/document-index.md

@@ -2,6 +2,12 @@
 
 Use the `documentIndex` operator (or the `di` shorthand) to select nodes of a particular document.
 
+{% hint style="warning" %}
+Note that versions prior to 4.18 require the 'eval/e' command to be specified. 
+
+`yq e <exp> <file>`
+{% endhint %}
+
 ## Retrieve a document index
 Given a sample.yml file of:
 ```yaml

operators/encode-decode.md

@@ -22,6 +22,12 @@ CSV and TSV format both accept either a single array or scalars (representing a
 XML uses the `--xml-attribute-prefix` and `xml-content-name` flags to identify attributes and content fields.
 
 
+{% hint style="warning" %}
+Note that versions prior to 4.18 require the 'eval/e' command to be specified. 
+
+`yq e <exp> <file>`
+{% endhint %}
+
 ## Encode value as json string
 Given a sample.yml file of:
 ```yaml

operators/entries.md

@@ -2,6 +2,12 @@
 
 Similar to the same named functions in `jq` these functions convert to/from an object and an array of key-value pairs. This is most useful for performing operations on keys of maps.
 
+{% hint style="warning" %}
+Note that versions prior to 4.18 require the 'eval/e' command to be specified. 
+
+`yq e <exp> <file>`
+{% endhint %}
+
 ## to_entries Map
 Given a sample.yml file of:
 ```yaml

operators/env-variable-operators.md

@@ -17,6 +17,12 @@ yq '(.. | select(tag == "!!str")) |= envsubst' file.yaml
 ```
 
 
+{% hint style="warning" %}
+Note that versions prior to 4.18 require the 'eval/e' command to be specified. 
+
+`yq e <exp> <file>`
+{% endhint %}
+
 ## Read string environment variable
 Running
 ```bash
@@ -77,6 +83,28 @@ will output
 a: "12"
 ```
 
+## Dynamically update a path from an environment variable
+The env variable can be any valid yq expression.
+
+Given a sample.yml file of:
+```yaml
+a:
+  b:
+    - name: dog
+    - name: cat
+```
+then
+```bash
+pathEnv=".a.b[0].name"  valueEnv="moo" yq 'eval(strenv(pathEnv)) = strenv(valueEnv)' sample.yml
+```
+will output
+```yaml
+a:
+  b:
+    - name: moo
+    - name: cat
+```
+
 ## Dynamic key lookup with environment variable
 Given a sample.yml file of:
 ```yaml

operators/equals.md

@@ -12,6 +12,12 @@ It is most often used with the select operator to find particular nodes:
 select(.a == .b)
 ```
 
+{% hint style="warning" %}
+Note that versions prior to 4.18 require the 'eval/e' command to be specified. 
+
+`yq e <exp> <file>`
+{% endhint %}
+
 ## Match string
 Given a sample.yml file of:
 ```yaml

operators/eval.md

@@ -0,0 +1,54 @@
+# Eval
+
+Use `eval` to dynamically process an expression - for instance from an environment variable.
+
+`eval` takes a single argument, and evaluates that as a `yq` expression. Any valid expression can be used, beit a path `.a.b.c | select(. == "cat")`, or an update `.a.b.c = "gogo"`.
+
+Tip: This can be useful way parameterise complex scripts.
+
+{% hint style="warning" %}
+Note that versions prior to 4.18 require the 'eval/e' command to be specified. 
+
+`yq e <exp> <file>`
+{% endhint %}
+
+## Dynamically evaluate a path
+Given a sample.yml file of:
+```yaml
+pathExp: .a.b[] | select(.name == "cat")
+a:
+  b:
+    - name: dog
+    - name: cat
+```
+then
+```bash
+yq 'eval(.pathExp)' sample.yml
+```
+will output
+```yaml
+name: cat
+```
+
+## Dynamically update a path from an environment variable
+The env variable can be any valid yq expression.
+
+Given a sample.yml file of:
+```yaml
+a:
+  b:
+    - name: dog
+    - name: cat
+```
+then
+```bash
+pathEnv=".a.b[0].name"  valueEnv="moo" yq 'eval(strenv(pathEnv)) = strenv(valueEnv)' sample.yml
+```
+will output
+```yaml
+a:
+  b:
+    - name: moo
+    - name: cat
+```
+

operators/file-operators.md

@@ -10,6 +10,12 @@ Note the use of eval-all to ensure all documents are loaded into memory.
 yq eval-all 'select(fi == 0) * select(filename == "file2.yaml")' file1.yaml file2.yaml
 ```
 
+{% hint style="warning" %}
+Note that versions prior to 4.18 require the 'eval/e' command to be specified. 
+
+`yq e <exp> <file>`
+{% endhint %}
+
 ## Get filename
 Given a sample.yml file of:
 ```yaml

operators/flatten.md

@@ -1,6 +1,12 @@
 # Flatten
 This recursively flattens arrays.
 
+{% hint style="warning" %}
+Note that versions prior to 4.18 require the 'eval/e' command to be specified. 
+
+`yq e <exp> <file>`
+{% endhint %}
+
 ## Flatten
 Recursively flattens all arrays
 

operators/group-by.md

@@ -2,6 +2,12 @@
 
 This is used to group items in an array by an expression.
 
+{% hint style="warning" %}
+Note that versions prior to 4.18 require the 'eval/e' command to be specified. 
+
+`yq e <exp> <file>`
+{% endhint %}
+
 ## Group by field
 Given a sample.yml file of:
 ```yaml

operators/has.md

@@ -2,6 +2,12 @@
 
 This is operation that returns true if the key exists in a map (or index in an array), false otherwise.
 
+{% hint style="warning" %}
+Note that versions prior to 4.18 require the 'eval/e' command to be specified. 
+
+`yq e <exp> <file>`
+{% endhint %}
+
 ## Has map key
 Given a sample.yml file of:
 ```yaml

operators/keys.md

@@ -2,6 +2,12 @@
 
 Use the `keys` operator to return map keys or array indices. 
 
+{% hint style="warning" %}
+Note that versions prior to 4.18 require the 'eval/e' command to be specified. 
+
+`yq e <exp> <file>`
+{% endhint %}
+
 ## Map keys
 Given a sample.yml file of:
 ```yaml

operators/length.md

@@ -2,6 +2,12 @@
 
 Returns the lengths of the nodes. Length is defined according to the type of the node.
 
+{% hint style="warning" %}
+Note that versions prior to 4.18 require the 'eval/e' command to be specified. 
+
+`yq e <exp> <file>`
+{% endhint %}
+
 ## String length
 returns length of string
 

operators/load.md

@@ -13,6 +13,12 @@ a: apple is included
 b: cool
 ```
 
+{% hint style="warning" %}
+Note that versions prior to 4.18 require the 'eval/e' command to be specified. 
+
+`yq e <exp> <file>`
+{% endhint %}
+
 ## Simple example
 Given a sample.yml file of:
 ```yaml

operators/map.md

@@ -2,6 +2,12 @@
 
 Maps values of an array. Use `map_values` to map values of an object.
 
+{% hint style="warning" %}
+Note that versions prior to 4.18 require the 'eval/e' command to be specified. 
+
+`yq e <exp> <file>`
+{% endhint %}
+
 ## Map array
 Given a sample.yml file of:
 ```yaml

operators/multiply-merge.md

@@ -22,6 +22,12 @@ Note the use of `eval-all` to ensure all documents are loaded into memory.
 yq eval-all 'select(fileIndex == 0) * select(fileIndex == 1)' file1.yaml file2.yaml
 ```
 
+{% hint style="warning" %}
+Note that versions prior to 4.18 require the 'eval/e' command to be specified. 
+
+`yq e <exp> <file>`
+{% endhint %}
+
 ## Multiply integers
 Given a sample.yml file of:
 ```yaml
@@ -262,18 +268,23 @@ will output
 ```
 
 ## Merge arrays of objects together, matching on a key
+
+This is a fairly complex expression - you can use it as is by providing the environment variables as seen in the example below.
+
+It merges in the array provided in the second file into the first - matching on equal keys.
+
+Explanation:
+
 The approach, at a high level, is to reduce into a merged map (keyed by the unique key)
 and then convert that back into an array.
 
-First the expression will create a map from the arrays keyed by '.a', the unique field we want to merge by.
+First the expression will create a map from the arrays keyed by the idPath, the unique field we want to merge by.
 The reduce operator is merging '({}; . * $item )', so array elements with the matching key will be merged together.
 
 Next, we convert the map back to an array, using reduce again, concatenating all the map values together.
 
 Finally, we set the result of the merged array back into the first doc.
 
-To use this, you will need to update '.myArray' in the expression to your array (e.g. .my.array), and '.a' to be the key field of your array (e.g. '.name')
-
 Thanks Kev from [stackoverflow](https://stackoverflow.com/a/70109529/1168223)
 
 
@@ -290,7 +301,7 @@ something: else
 ```
 And another sample another.yml file of:
 ```yaml
-myArray:
+newArray:
   - a: banana
     c: bananaC
   - a: apple
@@ -300,12 +311,12 @@ myArray:
 ```
 then
 ```bash
-yq eval-all '
+idPath=".a"  originalPath=".myArray"  otherPath=".newArray" yq eval-all '
 (
-  ((.myArray[] | {.a: .}) as $item ireduce ({}; . * $item )) as $uniqueMap
+  (( (eval(strenv(originalPath)) + eval(strenv(otherPath)))  | .[] | {(eval(strenv(idPath))):  .}) as $item ireduce ({}; . * $item )) as $uniqueMap
   | ( $uniqueMap  | to_entries | .[]) as $item ireduce([]; . + $item.value)
 ) as $mergedArray
-| select(fi == 0) | .myArray = $mergedArray
+| select(fi == 0) | (eval(strenv(originalPath))) = $mergedArray
 ' sample.yml another.yml
 ```
 will output

operators/parent.md

@@ -2,6 +2,12 @@
 
 Parent simply returns the parent nodes of the matching nodes.
 
+{% hint style="warning" %}
+Note that versions prior to 4.18 require the 'eval/e' command to be specified. 
+
+`yq e <exp> <file>`
+{% endhint %}
+
 ## Simple example
 Given a sample.yml file of:
 ```yaml

operators/path.md

@@ -4,6 +4,12 @@ The path operator can be used to get the traversal paths of matching nodes in an
 
 You can get the key/index of matching nodes by using the `path` operator to return the path array then piping that through `.[-1]` to get the last element of that array, the key.
 
+{% hint style="warning" %}
+Note that versions prior to 4.18 require the 'eval/e' command to be specified. 
+
+`yq e <exp> <file>`
+{% endhint %}
+
 ## Map path
 Given a sample.yml file of:
 ```yaml

operators/pipe.md

@@ -2,6 +2,12 @@
 
 Pipe the results of an expression into another. Like the bash operator.
 
+{% hint style="warning" %}
+Note that versions prior to 4.18 require the 'eval/e' command to be specified. 
+
+`yq e <exp> <file>`
+{% endhint %}
+
 ## Simple Pipe
 Given a sample.yml file of:
 ```yaml

operators/recursive-descent-glob.md

@@ -19,6 +19,12 @@ For instance to set the `style` of all nodes in a yaml doc, including the map ke
 ```bash
 yq '... style= "flow"' file.yaml
 ```
+{% hint style="warning" %}
+Note that versions prior to 4.18 require the 'eval/e' command to be specified. 
+
+`yq e <exp> <file>`
+{% endhint %}
+
 ## Recurse map (values only)
 Given a sample.yml file of:
 ```yaml

operators/reduce.md

@@ -21,6 +21,12 @@ Reduce syntax in `yq` is a little different from `jq` - as `yq` (currently) isn'
 
 To that end, the reduce operator is called `ireduce` for backwards compatability if a `jq` like prefix version of `reduce` is ever added.
 
+{% hint style="warning" %}
+Note that versions prior to 4.18 require the 'eval/e' command to be specified. 
+
+`yq e <exp> <file>`
+{% endhint %}
+
 ## Sum numbers
 Given a sample.yml file of:
 ```yaml

operators/select.md

@@ -2,6 +2,12 @@
 
 Select is used to filter arrays and maps by a boolean expression.
 
+{% hint style="warning" %}
+Note that versions prior to 4.18 require the 'eval/e' command to be specified. 
+
+`yq e <exp> <file>`
+{% endhint %}
+
 ## Select elements from array using wildcard prefix
 Given a sample.yml file of:
 ```yaml

operators/sort-keys.md

@@ -12,6 +12,12 @@ diff file1.yml file2.yml
 
 Note that `yq` does not yet consider anchors when sorting by keys - this may result in invalid yaml documents if your are using merge anchors.
 
+{% hint style="warning" %}
+Note that versions prior to 4.18 require the 'eval/e' command to be specified. 
+
+`yq e <exp> <file>`
+{% endhint %}
+
 ## Sort keys of map
 Given a sample.yml file of:
 ```yaml

operators/sort.md

@@ -4,6 +4,12 @@ Sorts an array. Use `sort` to sort an array as is, or `sort_by(exp)` to sort by
 
 Note that at this stage, `yq` only sorts scalar fields.
 
+{% hint style="warning" %}
+Note that versions prior to 4.18 require the 'eval/e' command to be specified. 
+
+`yq e <exp> <file>`
+{% endhint %}
+
 ## Sort by string field
 Given a sample.yml file of:
 ```yaml

operators/split-into-documents.md

@@ -2,6 +2,12 @@
 
 This operator splits all matches into separate documents
 
+{% hint style="warning" %}
+Note that versions prior to 4.18 require the 'eval/e' command to be specified. 
+
+`yq e <exp> <file>`
+{% endhint %}
+
 ## Split empty
 Running
 ```bash

operators/string-operators.md

@@ -43,6 +43,12 @@ IFS= read -rd '' output < <(cat my_file)
 output=$output ./yq '.data.values = strenv(output)' first.yml
 ```
 
+{% hint style="warning" %}
+Note that versions prior to 4.18 require the 'eval/e' command to be specified.&#x20;
+
+`yq e <exp> <file>`
+{% endhint %}
+
 ## Join strings
 Given a sample.yml file of:
 ```yaml

operators/style.md

@@ -2,6 +2,12 @@
 
 The style operator can be used to get or set the style of nodes (e.g. string style, yaml style)
 
+{% hint style="warning" %}
+Note that versions prior to 4.18 require the 'eval/e' command to be specified. 
+
+`yq e <exp> <file>`
+{% endhint %}
+
 ## Update and set style of a particular node (simple)
 Given a sample.yml file of:
 ```yaml

operators/subtract.md

@@ -2,6 +2,12 @@
 
 You can use subtract to subtract numbers, as well as removing elements from an array.
 
+{% hint style="warning" %}
+Note that versions prior to 4.18 require the 'eval/e' command to be specified. 
+
+`yq e <exp> <file>`
+{% endhint %}
+
 ## Array subtraction
 Running
 ```bash

operators/tag.md

@@ -2,6 +2,12 @@
 
 The tag operator can be used to get or set the tag of nodes (e.g. `!!str`, `!!int`, `!!bool`).
 
+{% hint style="warning" %}
+Note that versions prior to 4.18 require the 'eval/e' command to be specified. 
+
+`yq e <exp> <file>`
+{% endhint %}
+
 ## Get tag
 Given a sample.yml file of:
 ```yaml

operators/traverse-read.md

@@ -2,6 +2,12 @@
 
 This is the simplest (and perhaps most used) operator, it is used to navigate deeply into yaml structures.
 
+{% hint style="warning" %}
+Note that versions prior to 4.18 require the 'eval/e' command to be specified. 
+
+`yq e <exp> <file>`
+{% endhint %}
+
 ## Simple map navigation
 Given a sample.yml file of:
 ```yaml

operators/union.md

@@ -2,6 +2,12 @@
 
 This operator is used to combine different results together.
 
+{% hint style="warning" %}
+Note that versions prior to 4.18 require the 'eval/e' command to be specified. 
+
+`yq e <exp> <file>`
+{% endhint %}
+
 ## Combine scalars
 Running
 ```bash

operators/unique.md

@@ -2,6 +2,12 @@
 
 This is used to filter out duplicated items in an array.
 
+{% hint style="warning" %}
+Note that versions prior to 4.18 require the 'eval/e' command to be specified. 
+
+`yq e <exp> <file>`
+{% endhint %}
+
 ## Unique array of scalars (string/numbers)
 Given a sample.yml file of:
 ```yaml

operators/variable-operators.md

@@ -4,6 +4,12 @@ Like the `jq` equivalents, variables are sometimes required for the more complex
 
 Note that there is also an additional `ref` operator that holds a reference (instead of a copy) of the path, allowing you to make multiple changes to the same path.
 
+{% hint style="warning" %}
+Note that versions prior to 4.18 require the 'eval/e' command to be specified. 
+
+`yq e <exp> <file>`
+{% endhint %}
+
 ## Single value variable
 Given a sample.yml file of:
 ```yaml

operators/with.md

@@ -2,6 +2,12 @@
 
 Use the `with` operator to conveniently make multiple updates to a deeply nested path, or to update array elements relatively to each other. The first argument expression sets the root context, and the second expression runs against that root context.
 
+{% hint style="warning" %}
+Note that versions prior to 4.18 require the 'eval/e' command to be specified. 
+
+`yq e <exp> <file>`
+{% endhint %}
+
 ## Update and style
 Given a sample.yml file of:
 ```yaml

usage/convert.md

@@ -4,6 +4,12 @@ Encode and decode to and from JSON. Note that YAML is a _superset_ of JSON - so
 
 This means you don't need to 'convert' a JSON file to YAML - however if you want idiomatic YAML styling, then you can use the `-P/--prettyPrint` flag, see examples below.
 
+{% hint style="warning" %}
+Note that versions prior to 4.18 require the 'eval/e' command to be specified. 
+
+`yq e <exp> <file>`
+{% endhint %}
+
 ## Parse json: simple
 JSON is a subset of yaml, so all you need to do is prettify the output
 

usage/properties.md

@@ -1,11 +1,19 @@
-# Working with Properties
+# Properties
 
-## Yaml to Properties
+Encode to a property file (decode not yet supported). Line comments on value nodes will be copied across.
 
-To convert to property file format, use `--outputformat=props` or `-o=p`. Porting the comments from the `yaml` file to the property file is still in progress, currently line comments on the node values will be copied across. 
+By default, empty maps and arrays are not encoded - see below for an example on how to encode a value for these.
 
-Given a sample file of:
+{% hint style="warning" %}
+Note that versions prior to 4.18 require the 'eval/e' command to be specified. 
 
+`yq e <exp> <file>`
+{% endhint %}
+
+## Encode properties
+Note that empty arrays and maps are not encoded by default.
+
+Given a sample.yml file of:
 ```yaml
 # block comments don't come through
 person: # neither do comments on maps
@@ -13,17 +21,16 @@ person: # neither do comments on maps
     pets: 
     - cat # comments on array values appear
     food: [pizza] # comments on arrays do not
-```
+emptyArray: []
+emptyMap: []
 
+```
 then
-
 ```bash
-yq -o=p sample.yaml
-```
-
-will output:
-
+yq -o=props -I=0 '.' sample.yml
 ```
+will output
+```properties
 # comments on values appear
 person.name = Mike
 
@@ -32,3 +39,58 @@ person.pets.0 = cat
 person.food.0 = pizza
 ```
 
+## Encode properties: no comments
+Given a sample.yml file of:
+```yaml
+# block comments don't come through
+person: # neither do comments on maps
+    name: Mike # comments on values appear
+    pets: 
+    - cat # comments on array values appear
+    food: [pizza] # comments on arrays do not
+emptyArray: []
+emptyMap: []
+
+```
+then
+```bash
+yq -o=props -I=0 '... comments = ""' sample.yml
+```
+will output
+```properties
+person.name = Mike
+person.pets.0 = cat
+person.food.0 = pizza
+```
+
+## Encode properties: include empty maps and arrays
+Use a yq expression to set the empty maps and sequences to your desired value.
+
+Given a sample.yml file of:
+```yaml
+# block comments don't come through
+person: # neither do comments on maps
+    name: Mike # comments on values appear
+    pets: 
+    - cat # comments on array values appear
+    food: [pizza] # comments on arrays do not
+emptyArray: []
+emptyMap: []
+
+```
+then
+```bash
+yq -o=props -I=0 '(.. | select( (tag == "!!map" or tag =="!!seq") and length == 0)) = ""' sample.yml
+```
+will output
+```properties
+# comments on values appear
+person.name = Mike
+
+# comments on array values appear
+person.pets.0 = cat
+person.food.0 = pizza
+emptyArray = 
+emptyMap = 
+```
+

usage/xml.md

@@ -6,6 +6,12 @@ Consecutive xml nodes with the same name are assumed to be arrays.
 
 XML content data and attributes are created as fields. This can be controlled by the `'--xml-attribute-prefix` and `--xml-content-name` flags - see below for examples.
 
+{% hint style="warning" %}
+Note that versions prior to 4.18 require the 'eval/e' command to be specified. 
+
+`yq e <exp> <file>`
+{% endhint %}
+
 ## Parse xml: simple
 Notice how all the values are strings, see the next example on how you can fix that.