Kubernetes Helm, combine two variables with a string in the middle

Question

I’m trying to change the value of a variable if another variable it set by combining the two with a dash in the middle, I’m not sure of the syntax to do this, I’m thinking of somethings like:

{{- $serviceNamespace := .Values.serviceNamespace -}}
{{- $serviceTag := .Values.serviceTag -}}
{{- if $serviceTag}}
{{- $serviceNamespace := .Values.serviceNamespace  "-" .Values.serviceTag -}}
{{- end}}

Is this correct? if serviceNamespace was hello and serviceTag was 1.0.0 would I end up with serviceNamespace being hello-1.0.0?

What is the need for reassigning $serviceNamespace variable again. Why can't use (( $serviceNamespace }} - {{ $serviceTag }}? — Bimal
– Bimal, Commented Jul 25, 2017 at 0:49

abinet · Accepted Answer · 2017-07-25 15:43:37Z

127

For concatenation just use printf:

{{-  $serviceNamespace := printf "%s-%s" .Values.serviceNamespace .Values.serviceTag -}}

answered Jul 25, 2017 at 15:43

abinet

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3 Comments

A. Rabus Over a year ago

This gives me an error "mapping values are not allowed in this context" on helm install, but still works... ???

dokun1 Over a year ago

Thank you for this. I'm going to post an issue to their github repo which shows how I used this to avoid a string casting issue to int inside a range loop!

Adiii Over a year ago

or if you want to concatenate string name: {{ .Release.Name }}-mystring-chart

Gabriel Wu · Accepted Answer · 2020-07-13 10:50:29Z

85

You can simply do it like this , with string ":" in middle

"{{ $values.image.repository }}:{{ $values.image.tag }}"

answered Jul 13, 2020 at 10:50

Gabriel Wu

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2 Comments

Any1 Over a year ago

How would you apply a function with a pipe to this then?

Mohammed Noureldin Over a year ago

@Any1 have you found out how to pass this into a pipe?

David · Accepted Answer · 2020-06-12 18:02:23Z

Update

It is now possible in the 1.11 version of golang, see commit:

{{- $serviceNamespace := .Values.serviceNamespace -}}
{{- $serviceTag := .Values.serviceTag -}}
{{- if $serviceTag}}
{{- $serviceNamespace = print .Values.serviceNamespace  "-" .Values.serviceTag -}}
{{- end}}

Notice the new = operator in $serviceNamespace = print .Values.serviceNamespace "-" .Values.serviceTag

Older golang versions

You cannot currently (in golang 1.9, but available in 1.11, see update above) reassign template variables because if introduces a new scope. Until this is fixed (see issue and proposed fix), you can work around this by writing a function:

{{ define "makeServiceNamespace" }}
    {{- if .Values.serviceTag }}
    {{- printf "%s-%s" .Values.serviceNamespace .Values.serviceTag -}}
    {{- else }}
    {{- print .Values.serviceNamespace }}
    {{- end }}
{{- end }}

Then use it like so:

serviceNamespace: {{ template makeServiceNamespace . }}

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