Usage Examples¶

Several files are available in examples folder you can cd into the folder and test the following cases.

Multiple cases are defined in example.tpl file, you can change values and observe output based on that.

INTERVAL=2s OUTPUT_INFLUXDB_ENABLED=true \
HOSTNAME=localhost subvars < example.tpl

Output:

[agent]
  ## Default data collection interval for all inputs
  interval = "2s"
  round_interval = true
  hostname = "localhost"

[[outputs.influxdb]]

# kafka output is disabled

This example is included to show how specific case where you would not like to render {{ $labels.instace }} with subvars and only threshold value.

ALERT_THRESHOLD=5 subvars < prometheus_alert.conf

Output:

- alert: HighRequestLatency
    expr: api_http_request_latencies_second{quantile="0.5"} > 5
    for: 10m
    annotations:
      summary: "High request latency on {{ $labels.instance }}"

You can use the builtin match function to only match variables starting with defined prefix pattern.

PROD_REGION=us-east-1 PROD_DATACENTER=data-center-1 \
TEST_REGION=eu-centeral-1 subvars < match.tpl

Output:

Environment variables starting with PROD_:
PROD_DATACENTER="data-center-1"
PROD_REGION="us-east-1"

subvars will render all the files in examples folder and save each rendered file to conf folder.

PROD_REGION=eu-west-1 PROD_DATACENTER=dc1 TEST_REGION=eu-centeral-1 \
INTERVAL=5s OUTPUT_INFLUXDB_ENABLED=true HOSTNAME=localhost subvars \
dir --input examples --out conf

Missing Key Behaviour¶

--missingkey invalid (default)

echo "Hey! {{ .USER }} your home folder is {{ .MYHOME }}" | subvars

Output:

Hey! Jon your home folder is <no value>

--missingkey zero

echo "Hey! {{ .USER }} your home folder is {{ .MYHOME }}" | subvars --missingkey zero

Output:

Hey! Jon your home folder is

--missingkey error

echo "Hey! {{ .USER }} your home folder is {{ .MYHOME }}" | subvars --missingkey error

Output:

Hey! Jon your home folder is 2021/07/09 20:51:45 template: :1:40: 
executing "" at <.MYHOME>: map has no entry for key "MYHOME"
exit status 1

Template Functions¶

In addition to the standard set of template actions and functions that come with Go, subvars also incorporates sprig for additional, commonly used functions.

echo "Hey! {{ .USER | upper }} your home folder is {{ .HOME }}" | subvars

In the example, the username will be converted to upper case letters.