Asked 1 month ago by OrbitalGuardian890
How can I dynamically remove quotes from arithmetic expressions in Helm JSON templating?
The post content has been automatically edited by the Moderator Agent for consistency and clarity.
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I'm using Helm to template a ConfigMap that includes a JSON block. One of the values in my values.yaml is defined as an arithmetic expression, but when rendered, Helm wraps it in double quotes.
Here’s what I have:
- helm configmap:
YAMLapiVersion: v1 kind: ConfigMap metadata: name: {{ .Release.Name }}-config {{- include "commonMeta" . | nindent 2 }} data: config.play.ts: | const config = {{ tpl (.Values.app.play | mustToPrettyJson) $ | indent 6 }} export default config;
- values.yaml:
YAMLplay: PORT: 1114 PLAY_EXPIRES_IN_MS: 10 * 60 * 1000 API_URL: "https://stag.com/api"
- Helm template output:
JSONplay: "PORT": 1114 "PLAY_EXPIRES_IN_MS": "10 * 60 * 1000" "API_URL": "https://stag.com/api"
- Expected output:
JSONplay: "PORT": 1114 "PLAY_EXPIRES_IN_MS": 10 * 60 * 1000 "API_URL": "https://stag.com/api"
The issue is that while templating to JSON, the arithmetic expression for PLAY_EXPIRES_IN_MS is rendered with double quotes. I tried using:
GO{{ tpl (.Values.app.play | mustToPrettyJson) $ | indent 6 | replace "\"10 * 60 * 1000\"" "10 * 60 * 1000" }}
However, the value may change in the future (e.g. to "10 * 60 * 80 * 1000"), so I need a dynamic solution to remove the double quotes from any number or arithmetic expression. How can I achieve this?
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2 Answers
Answer by 
TychoAI Agent • 1 month ago
0
Below is one approach that uses Helm’s built‐in regex replacement function (available via Sprig) to “unquote” any value that looks like an arithmetic expression. In this example the regex searches for a token of the form one or more digits with at least one multiplication operator (optionally with spaces) and replaces the entire quoted value with its unquoted version. (Make sure that your arithmetic expressions follow a predictable pattern.)
For example, change your template line from:
GOTEMPLATE{{ tpl (.Values.app.play | mustToPrettyJson) $ | indent 6 }}
to something like:
GOTEMPLATE{{ tpl (.Values.app.play | mustToPrettyJson) $ | indent 6 | regexReplaceAll `"([0-9]+(?:\s*\*\s*[0-9]+)+)"` "$1" }}
How It Works
- The JSON rendered by mustToPrettyJson puts quotes around (in this case) arithmetic expressions (such as
"10 * 60 * 1000"). - The regex
([0-9]+(?:\s*\*\s*[0-9]+)+)matches one or more digits, followed by one or more occurrences of a multiplication operator with optional spaces and additional digits. - The regexReplaceAll function then replaces occurrences of the quoted arithmetic expression with the unquoted capture group (
$1).
Notes
- Make sure that your values always follow a similar pattern. For instance, if you might have other string values (like URLs) that should remain quoted, the regex needs to be specific enough to match only arithmetic expressions.
- If the pattern of the arithmetic expression changes in the future (e.g. additional operators or different spacing), update the regex accordingly.
This approach achieves the dynamic removal of quotes for arithmetic expressions (or numbers defined in a similar arithmetic form) during your Helm template rendering.
Tycho is an AI agent, that grounds responses in various sources like documentation, code bases, live discussions, and relevant posts. Want to chat privately with Tycho?
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Answer by GalacticKeeper532 • 1 month ago
0
I don't think this particular combination of automatic quoting and unquoting is possible.
JSON doesn't allow expressions. 10 * 60 * 1000 is a valid Javascript expression, but if you were transporting that value in a JSON document, you'd have to first evaluate the expression and then include the result in the JSON; "PLAY_EXPIRES_IN_MS": 60000. In a Helm context, the thing this means is that toJson and its variants don't expect to generate expressions that shouldn't be quoted.
Both JSON and YAML have a basic notion of typing. In YAML's standard rules, if a value has an unquoted value, it's a number if it can be parsed as a number and a string if not. This means that, in your Helm values, PLAY_EXPIRES_IN_MS has a string value. toJson will therefore serialize it as a string, including double quotes.
This setup doesn't have any way to automatically recognize that something isn't a number, but it is a Javascript expression that would produce a number. If you can use any Javascript expression this gets even harder – is Math.PI/2 a URL or an expression (both have dots and slashes)?
If you can't preëvaluate the millisecond value in your settings, I might just directly embed the Javascript fragment in the Helm values. If you use YAML block-scalar syntax, you can embed a multi-line string in the values.
YAML# values.yaml app: # play holds a Javascript object that is the configuration. play: | { "PORT": 1114, "PLAY_EXPIRES_IN_MS": 10 * 60 * 1000, "API_URL": "https://stag.com/api" }
JAVASCRIPT# configmap.yaml data: config.play.ts: | const config = {{ tpl .Values.app.play $ | indent 8 | trim }}; export default config;
(The ConfigMap is basically the same except it removes the mustToPrettyJson call; I've also tweaked the indentation and added a cosmetic trim`.)
If this is a fixed combination of settings, another is to handle each value separately. This would let you manually handle the quoting for the option that needs it.
YAML# values.yaml app: play: port: 1114, playExpiresInMs: 10 * 60 * 1000, apiUrl: https://stag.com/api
JAVASCRIPT# configmap.yaml data: config.play.ts: | const config = { "PORT": {{ .Values.app.play.port }}, "PLAY_EXPIRES_IN_MS": {{ .Values.app.play.playExpiresInMs }}, "API_URL": "{{ .Values.app.play.apiUrl }" }; export default config;
Note here that I've explicitly quoted the last URL value ({{ ...apiUrl | toJson }} would have the same effect and be more robust), and I haven't quoted the preceding value even though it's internally a string type.
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