README
¶
envsubst 
Environment variables substitution for Go. see docs below
Installation:
$ go get github.com/a8m/envsubst/cmd/envsubst
Using via cli
$ envsubst < input.tmpl > output.text
$ echo 'welcome $HOME ${USER:=a8m}' | envsubst
$ envsubst -help
Imposing restrictions
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:
| Flag | Meaning |
|---|---|
-no-unset |
fail if a variable is not set |
-no-empty |
fail if a variable is set but empty |
These flags can be combined to form tighter restrictions.
Using envsubst programmatically ?
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")
}
Docs
api docs here:
| Expression | Meaning |
|---|---|
${var} |
Value of var (same as $var) |
${var-$DEFAULT} |
If var not set, evaluate expression as $DEFAULT |
${var:-$DEFAULT} |
If var not set or is empty, evaluate expression as $DEFAULT |
${var=$DEFAULT} |
If var not set, evaluate expression as $DEFAULT |
${var:=$DEFAULT} |
If var not set or is empty, evaluate expression as $DEFAULT |
${var+$OTHER} |
If var set, evaluate expression as $OTHER, otherwise as empty string |
${var:+$OTHER} |
If var set, evaluate expression as $OTHER, otherwise as empty string |
| table taken from here |
See also
os.ExpandEnv(s string) string- only supports$varand${var}notations
License
MIT
Documentation
¶
Index ¶
- func Bytes(b []byte) ([]byte, error)
- func BytesRestricted(b []byte, noUnset, noEmpty bool) ([]byte, error)
- func ReadFile(filename string) ([]byte, error)
- func ReadFileRestricted(filename string, noUnset, noEmpty bool) ([]byte, error)
- func String(s string) (string, error)
- func StringRestricted(s string, noUnset, noEmpty bool) (string, error)
Constants ¶
This section is empty.
Variables ¶
This section is empty.
Functions ¶
func Bytes ¶
Bytes returns the bytes represented by the parsed template after processing it. If the parser encounters invalid input, it returns an error describing the failure.
func BytesRestricted ¶
BytesRestricted returns the bytes represented by the parsed template after processing it. If the parser encounters invalid input, or a restriction is violated, it returns an error describing the failure.
func ReadFile ¶
ReadFile call io.ReadFile with the given file name. If the call to io.ReadFile failed it returns the error; otherwise it will call envsubst.Bytes with the returned content.
func ReadFileRestricted ¶
ReadFileRestricted calls io.ReadFile with the given file name. If the call to io.ReadFile failed it returns the error; otherwise it will call envsubst.Bytes with the returned content.
Types ¶
This section is empty.
Source Files
Directories