Environment variables substitution for Go. see docs below

go get github.com/a8m/envsubst/cmd/envsubst

The envsubst binary is also available via Github releases

curl -L https://github.com/a8m/envsubst/releases/download/v1.1.0/envsubst-`uname -s`-`uname -m` -o envsubst
chmod +x envsubst
sudo mv envsubst /usr/local/bin

envsubst < input.tmpl > output.text
echo 'welcome $HOME ${USER:=a8m}' | envsubst
envsubst -help

There are two command line flags with which you can cause the substitution to stop with an error code, should the restriction associated with the flag not be met. This can be handy if you want to avoid creating e.g. configuration files with unset or empty parameters. The flags and their restrictions are:

These flags can be combined to form tighter restrictions.

You can take a look on _example/main or see the example below.

package main

import (
	"fmt"
	"github.com/a8m/envsubst"
)

func main() {
    input := "welcom $HOME"
    str, err := envsubst.String(input)
    // ...
    buf, err := envsubst.Bytes([]byte(input))
    // ...
    buf, err := envsubst.ReadFile("filename")
}

api docs here:

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• os.ExpandEnv(s string) string - only supports $var and ${var} notations

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