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Extracting string in `helm helper template` using regexp

1/14/2019

I am trying to extract a certain string obtained from values.yaml in _helper.tpl. Basically, I am trying to extract the string localhost from mongodb://localhost:30010

In my _helper.tpl

{{- define "myservice.mongodbcache.bindip" -}}
{{- regexFind "\/\.(.*):" ( .Values.myservice.cachedb.uri | toString ) -}}
{{- end -}}

my values.yml file

myservice:
  cachedb:
    uri: "mongodb://localhost:30010"

and in my configmap, I want to use it the following way

apiVersion: v1
kind: ConfigMap
metadata:
  name: {{ .Release.Name }}-myservice-configmap
  namespace: {{ .Release.Namespace }}
data:
  myservice.mongodbcache.bind.ip: {{ template "myservice.mongodbcache.bindip" }}

However, I keep getting this error, when I try to dry run

Error: parse error in "tree-helm/templates/_helpers.tpl": template: tree-helm/templates/_helpers.tpl:35: invalid syntax

Line 35 is the one with regexFind

-- kosta

go-templates

kubernetes-helm

regex

2 Answers

1/14/2019

To get the host from a URL, you would need to use Lookahead and Lookbehind. Please see the example

Unfortunately, you can not write this type of regex in helm. You will get the following error:

Error: rendering template failed: regexp: Compile(`(?<=://)(.*?)(?=:)`): error parsing regexp: invalid or unsupported Perl syntax: `(?<`

From chart template guide:

It is considered preferable to use include over template in Helm templates simply so that the output formatting can be handled better for YAML documents.

Working with include, you can get the hostname or ip the following way:

configmap.yaml

apiVersion: v1
kind: ConfigMap
metadata:
  name: {{ .Release.Name }}-myservice-configmap
  namespace: {{ .Release.Namespace }}
data:
  myservice.mongodbcache.bind.ip: {{- include "myservice.mongodbcache.bindip" . -}}

_helpers.tpl

{{- define "myservice.mongodbcache.bindip" -}}
{{- $match := .Values.myservice.cachedb.uri | toString | regexFind "//.*:" -}}
{{- $match | trimAll ":" | trimAll "/" -}}
{{- end -}}

Ore even have it all in one line.

Result

$ helm install --debug --dry-run .
....
# Source: mychart/templates/configmap.yaml
apiVersion: v1
kind: ConfigMap
metadata:
  name: billowing-boxer-myservice-configmap
  namespace: default
data:
  myservice.mongodbcache.bind.ip:localhost

-- edbighead

Source: StackOverflow

1/14/2019

\/\/(.*):

The regex that you can use to extract the string localhost from mongodb://localhost:30010

-- Keshav Kothari

Source: StackOverflow

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Extracting string in `helm helper template` using regexp

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