Yaml merge multiple anchors When there are duplicate keys, GitLab performs a reverse deep merge based on the keys. Jul 23, 2020 · The YAML merge key only works on mappings. import sys import ruamel. But then the resulting YAML is split into multiple documents before it is fed to Kubernetes. It makes yaml operations humanly :) Describe the bug Yaml merge drop anchors Version of yq: 4. An anchor is a value that is defined with an ampersand “&” followed by a name. Discover how to use anchors and aliases to create reusable content and simplify complex configurations. If the value associated with the key is a single mapping node, each of its key/value pairs is inserted into the current mapping, unless the key already exists in it. Aliases (*) are used to reference a value. For more complex scenarios involving multiple systems or dynamic configuration, other techniques like configuration management tools or templating languages may be more appropriate. yaml files containing yaml anchors Motivation We currently generate a decent amount of configuration via terraform, and save that into values. html go-yaml's behaviour is not a bug. Which would mean you are combining keys, all having null values. Note that the anchors and aliases are not required, but keeping them in to align with the question. dump(data, sys. 2). See also: How to merge YAML arrays? Nov 25, 2022 · First of all, thank you for this wonderful project. There are plans to add programmatic features in YAML 1. arrays) and are common to reduce repetition of same configuration directives that some files/systems tend to and/or sometimes just because one can May 27, 2019 · In #35 a syntax to merge sequences was proposed, but the syntax isn't going to happen, while I can understand that it would be useful to have a standard way of doing this. 🧠 Advanced YAML Features: Anchors, Aliases & Merge Keys Advanced YAML features like anchors (&), aliases (*), and merge keys (<<) enable efficient reuse and composition of data structures. You will need a templating engine like Jinja (commonly used with YAML, e. We recommend only using multiple documents per file when it is absolutely necessary. Nov 2, 2022 · perlpunk commented on Nov 30, 2022 I wouldn't expect an update. Apr 21, 2021 · Docker Compose lets you manage multiple Docker containers and their associated resources such as volumes and networks. yml Apr 3, 2023 · YAML anchors and aliases are a way to define a value once and reference it multiple times within a YAML document. Purpose yaml-merge is designed to merge two YAML files by combining sequences (arrays) under a specified key while handling duplicates intelligently. k. Aliases (*) act as a reference or Oct 2, 2020 · The yaml-merge tool can read per YAML Path merging options from an INI-Style configuration file via its --config (-c) argument. ) Update A solution for this issue was implemented in #266173 (closed) please review it first before adding your comment to this issue Problem to solve It is not possible to use multiple anchors to construct scripts or after_scripts, or any array in YAML. org/type/merge. Moreover, it is unnecessary since the merge key can take multiple maps as arguments: May 15, 2019 · I just added a feature called "Merge Keys" to YAML::PP. Discover how to efficiently organize and manage complex data in YAML format. Example 3 You may want to partially override values. Since the already commented issue#35 exists, merge-keys << doesn't help you. '<<' is a string key which some YAML loaders perform a merge operation on, and often in a manner incompatible with other YAML loaders. However if you are dealing with mappings, you can use the merge key language-independent type if your parser supports it to combine multiple sets of keys into a new mapping: Feb 19, 2023 · " First off, merge keys for objects use regular YAML syntax. This is particularly useful when: Managing infrastructure-as-code configurations Combining multiple environment configurations Merging deployment manifests Consolidating configuration files Jul 27, 2023 · Summary Support merge of values. No Perl YAML module supports this so far. job_template configuration, each with their own custom Aug 3, 2022 · I am not sure what you mean by "ruamel. Learn to use YAML anchors in GitLab CI/CD for reusable deployment job templates, reducing redundancy and simplifying pipeline maintenance. YAML has a feature called 'anchors' that you can use to duplicate content across your document. Instead you should work with sequences and use anchor & and alias *. User-defined tags Jan 18, 2005 · The “ <<” merge key is used to indicate that all the keys of one or more specified maps should be inserted into the current map. 6 No you cannot do that, an alias replaces a complete node. Upvoting indicates when questions and answers are useful. Jul 28, 2016 · 39 Your example is valid YAML (a convenient place to check is YPaste), but it's not defined what the merge does. It only merges/inserts referenced keys into a map (see YAML docs merge). g. 2 spec . 30. Document your use of merge keys to ensure clarity for other developers working with your YAML files. Fortunately there's a simple way to add string concatenation to YAML via user-defined tags. Mar 18, 2021 · I want to merge two yaml documents with the result containing all mapped values (with the last one taking precedence) concatenated arrays e. This problem may be better described us Sep 6, 2025 · YAML format is used in many config files, and here are a few tips to make your yaml files look nicer. Your docker-compose. It would work if GitLab automatically flattened nested lists in the . Jan 28, 2023 · I am trying to reuse anchor from one yaml file in another yaml file, parent-gitlab-ci. I would like to merge arrays in YAML, and load them via ruby - Oct 14, 2017 · Summary YAML anchors and aliases let you reference and use the same data multiple times within a single YAML document. Apr 19, 2022 · How to inherit/merge volumes from yaml anchors in docker-compose? Asked 3 years, 7 months ago Modified 3 years, 2 months ago Viewed 2k times Note: This issue may also be addressed with standard use of Anchors and Aliases in YAML. The merge key is YAML's one functional thing, and it's actually not even part of the YAML 1. Best Practices for Using Anchors and Aliases To make the most Feb 10, 2025 · You are not using the anchor host1 in a different YAML file. Some Jan 13, 2025 · Learn how to simplify Docker Compose configurations and avoid repetition with the power of Anchors, Aliases, and Extensions. yaml. You can use them to share default settings between services. yml animals: - elephant Apr 16, 2025 · You'll need to complete a few actions and gain 15 reputation points before being able to upvote. To reuse configuration from different YAML files, use !reference tags or the extends keyword. Per the spec, a merge key can have a value: A mapping, in which case it's merged into the parent mapping. given this file # file1. 1 which allows to mix-in only the changing mapping with a base (definition). Examples: >- means “treat single newline symbols ('\n') as spaces (' '), and remove all newlines at the end” (useful to put long requires the resultant list to be flattened, which leads to suggestions like adding a !flatten tag that will then have to be specially processed by whatever is the underlying parser (e. A sequence of mappings, in which case each is merged, one-by-one, into the parent mapping. May 29, 2024 · YAML Anchors and Alias # Anchors and Aliases are YAML constructions that allow you to reduce repeat syntax and extend existing data nodes. This feature, while sometimes overlooked, can be a game-changer for those looking to optimize their Docker workflows. Jul 12, 2023 · In YAML, it is possible to use anchors to define a hash and then override values using the “merge” operator <<, as so: . basic-cache: &readonly-cache key: cache-key paths: - path/to/whatever policy: pull my-job: cache: <<: &readonly-cache policy: pull-push However, anchors can only be used in a single YAML file (no includes), which led to the invention of !reference tags. In YAML, a multiline string is any string literal that spans multiple lines. It creates two jobs, test1 and test2, that inherit the . See interactive demo. You write declarative YAML files which Compose uses to create your container stack. Introduction This Jul 3, 2021 · Some of YAML's properties not in JSON are anchors, aliases and merge keys that can work well together. Solution use YAML aliases, with YAML merge keys in YAML, reusable "transclusion identifiers" are called anchors and aliases in YAML, reusable "transclusion identifiers" consist of alphanumeric tokens preceeded by an ampersand or asterisk Reset value In addition to the previously described mechanism, an override Compose file can also be used to remove elements from your application model. Consider using YAML Anchors in conjunction with merge keys for more complex reuse scenarios. Oct 6, 2020 · 26 While a quick test shows that PyYAML does support this, I would advise against it since having multiple identical keys (<<) in the same mapping violates the core YAML spec (both 1. 3, as @ing Apr 12, 2020 · The desired behavior can be achieved by using multiple docker-compose files, one for each volume. yaml anchor concatenation in script or after_script. in Ansible or SaltStack) to do such processing. Be mindful of the order when using multiple merge keys to prevent unintended overwrites. Many loaders treat a << key as a normal string key. yml configuration file. Reuse configuration with YAML anchors and fragmentsIf you have an anchor that you want to use in more than one service, use it in conjunction with an extension to make your Compose file easier to maintain. You can merge mappings defined elsewhere in your YAML document into other mappings with that. job_template configuration, each with their own custom Nov 6, 2022 · The YAML Spec defined a simple way to reuse values in YAML documents by means of Anchors and Aliases. YAML merge multiple arrays into one Asked 5 years, 6 months ago Modified 5 years, 6 months ago Viewed 5k times May 28, 2019 · Updated on May 28, 2019 in #docker Docker Tip #82: Using YAML Anchors and X Properties in Docker Compose YAML anchors let you reuse parts of your YAML file like functions. However, people find it useful and many YAML implementations (including YS) support it. So your example should look like this: Jun 27, 2020 · @Ben as an alternative answer next to YAML anchors is to combine it with Merge Key Language-Independent Type for YAML™ Version 1. This label can be used to reference the same data elsewhere in the YAML document, effectively creating a reusable component. Writing about YAML anchor, alias and merge-key in use for reference YAML nodes/data and YAML mixins Jan 3, 2017 · First off, merge keys for objects use regular YAML syntax. When using Bitbucket Pipelines, YAML anchors reduce effort and make updating in bulk, easier. You better rewrite your YAML. yaml unfortunately does merge tag1 anchor to tag2". 1 and 1. The following example uses anchors and map merging. e. You have an alias without an anchor in file2. YAML is a Superset of JSON Because YAML is a superset of JSON, any valid JSON document should be valid YAML. Use anchors with hidden jobs to provide templates for your jobs. So no, you can't define an anchor in one file and reference it in another file. Here is a short example: --- defaults: &defaults A: 1 B: 2 mapping: << : *defaults A: 23 C: 99 # same as: mapping: B: 2 A: 23 C: 99 If you don't know the &defaults/*defaults notation, here follows a basic Use merge keys to avoid repetition in your YAML configurations. yaml files to organize and override your application settings. Later Apr 14, 2022 · A YAML anchor is local to a single file. Anchors (&) are used to define a value. Learn how these features enhance data organization and readability in your YAML syntax. ‘<<’ is a string key which some YAML loaders perform a merge operation on, and often in a manner incompatible with other YAML loaders. Learn about complex structures in YAML, including nested lists, dictionaries, and advanced data representations. Fortunately there's a simple way to add string concatenation to YAML via custom tags in Python. It does not merge recursively; it just doesn't do anything for keys that already exist in the current mapping (which is the case in your code). stdout) this gives exactly the original input: tag1: &tag1 subtag1: 42 subtag2: baz tag2: <<: *tag1 subtag1: 18 subtag3: *tag1 So it preserves both Aug 24, 2024 · Anchors (&) allow you to define a block of data and label it with a unique name. yaml files we also have Feb 28, 2021 · gitlab-ci. 1 (2005) support block indicators to control how parser should handle multiline text. Anchors are only valid in the file they were defined in. load(file_in) yaml. However, it Jul 11, 2017 · There is an open issue for this on the GitLab issue tracker: gitlab-ci. Happy containerizing! If a service is defined in both files, Compose merges the configurations using the rules described below and in the Compose Specification. 4 Operating system: linux Installed via: binary- Aug 11, 2023 · YAML's anchors and aliases offer an efficient way to reuse parts of a document, making Docker Compose files more maintainable and readable. There must be many such uses. YAML() data = yaml. If your base docker-compose. Your use case of building up a path name from parts is a good example -- there must be many such uses. Anchors are particularly useful for defining commonly used configurations or settings that you want to reference multiple times without rewriting them. You can place Anchors (&) on an entity, such as & in YAML, to mark a multi-line section. Example This may look more complicated at first, but once you know what it’s doing it’s very simple and can greatly reduce the amount of duplication in your YAML May 13, 2019 · It seems that Ansible can pick up variable from different YAML files but YAML references using node anchors and merge keys will only work when in the same file. Learn about YAML anchors, a powerful feature for reducing repetition in YAML files. Jul 15, 2022 · YAML anchors and aliases are best suited for managing configuration within a single YAML file, where you need to reuse settings and reduce redundancy. Your YAML happens to be valid, but the value of array2 is the string '<< *my_array_alias - baz'. Feb 6, 2025 · Learn how to effectively manage configuration complexity in Helm by using multiple values. For this purpose, the custom YAML tag !reset can be set to override a value set by the overridden Compose file. yml files can become repetitive when you're working with a complex stack. Oct 16, 2020 · Introduction Rudimentary Example of Core Concepts Whole File Merge Document Fragment Merge CLI-Supplied Data Setting Complex Values Add an Element to the End of an Array Add Multiple Array Elements Add a New Record to an Array-of-Hashes This document is part of the body of knowledge about yaml-merge, one of the reference command-line tools provided by the YAML Path project. yaml') yaml = ruamel. Whereas the --arrays (-A) argument supplies an overarching mode for merging Arrays, using a configuration file permits far more precise control whenever you need a different mode for specific parts of the merge documents. How to merge multiple Compose files To use multiple override files, or an override file with a different name, you can either use the pre-defined COMPOSE_FILE environment variable, or use the -f option to specify the list of files. These allow references and mixins for hashes (not sequences a. What's reputation and how do I get it? Instead, you can save this post to reference later. Having multiple documents in a file can be difficult to debug. yaml that just happens to have same name as an anchor in a different file. Jun 27, 2025 · Explore YAML anchors and aliases in depth. Since Compose will merge settings when you use multiple Compose files, you don't really need to do this, though. Jun 2, 2025 · YAML Variables YAML itself isn't a functional programming language, but advanced users are probably aware of YAML's anchors, aliases and the merge key. Other people suggest using the merge key type feature. , script or after_script, rules, etc. For example: multiline_string: This string continues on a second line The ability to break strings over multiple lines is invaluable in YAML, as it allows you to represent complex content without cramming everything onto a single line. Jul 2, 2021 · This guide gives you examples for using YAML anchors, aliases, and overrides, which are features of the YAML language that help keep your code DRY. My suggestion is the official way to merge multiple anchors, see https://yaml. Your use case of building up a path name from parts is a good example. Compose follows the rule outlined by YAML merge type. gitlab-ci. Use anchors to duplicate or inherit properties. You can't use YAML anchors across multiple files when using the include keyword. Unfortunately, these workarounds aren't viable for me, because I need to do Feb 1, 2023 · 在这种情况下, 我们其实可以使用YAML的 Anchor (&)跟 Alias (*)来复用我们的配置. , PyYAML). Overrides (<<:) are used to merge values. What Are Multiline Strings in YAML? Let‘s start with a quick definition. a. . yml file says Feb 17, 2023 · Hi, I am attempting to merge two yaml files and would like any shared keys under a specific key to use values from one of the yaml files, and not merge both. Services might share configuration options, causing you to duplicate sections of your file. You can then use an Alias (*) call that anchor later in the document to reference that section. You can’t use YAML anchors across multiple files when using the include keyword. yaml from pathlib import Path file_in = Path('expand. It's surprising, since the purpose of YAML anchors & references is to factor duplication out of YAML data files, that there isn't a built-in way to concatenate strings using references. yaml syntax for merging YAML arrays (i. 首先我们可以使用Anchor来标记我们期望复用的配置, 我们知道YAML的结构其实也是一种树的结构, 那么Anchor标记的就可以是树里面任意树枝下的整个叶子结点. Multiline text values YAML since version 1. ctq lkuxhm trqjx ztgp ytmzgm kpmpo epr tvu kmnqq kev nfb glmf vswn upv bnderuzi