Environment variables substitution for Go. see docs below

Latest stable envsubst prebuilt binaries for 64-bit Linux, or Mac OS X are available via Github releases.

curl -L https://github.com/a8m/envsubst/releases/download/v1.2.0/envsubst-`uname -s`-`uname -m` -o envsubst
chmod +x envsubst
sudo mv envsubst /usr/local/bin

Download the latest prebuilt binary from releases page, or if you have curl installed:

curl -L https://github.com/a8m/envsubst/releases/download/v1.2.0/envsubst.exe

You can install via go get (provided you have installed go):

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

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

There are three 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. Setting a -fail-fast flag in conjunction with either no-unset or no-empty or both will result in a faster feedback loop, this can be especially useful when running through a large file or byte array input, otherwise a list of errors is returned.

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

api docs here:

_{Most of the rows in this table were taken from here}

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

MIT