README
¶
envsubst
Environment variables substitution for Go. see docs below
Installation:
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
Using via cli
envsubst < input.tmpl > output.text
echo 'welcome $HOME ${USER:=a8m}' | envsubst
envsubst -help
Imposing restrictions
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:
| Option | Meaning | Type | Default |
|---|---|---|---|
-i |
input file | ```string | stdin``` |
-o |
output file | ```string | stdout``` |
-no-digit |
do not replace variables starting with a digit, e.g. $1 and ${1} | flag |
false |
-no-unset |
fail if a variable is not set | flag |
false |
-no-empty |
fail if a variable is set but empty | flag |
false |
-fail-fast |
fails at first occurence of an error, if -no-empty or -no-unset flags were not specified this is ignored |
flag |
false |
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 |
$$var |
Escape expressions. Result will be $var. |
Most of the rows in this table were taken from here
See also
os.ExpandEnv(s string) string- only supports$varand${var}notations
License
MIT
Documentation
¶
Index ¶
- func Bytes(b []byte) ([]byte, error)
- func BytesRestricted(b []byte, noUnset, noEmpty bool) ([]byte, error)
- func BytesRestrictedNoDigit(b []byte, noUnset, noEmpty bool, noDigit bool) ([]byte, error)
- func ReadFile(filename string) ([]byte, error)
- func ReadFileRestricted(filename string, noUnset, noEmpty bool) ([]byte, error)
- func ReadFileRestrictedNoDigit(filename string, noUnset, noEmpty bool, noDigit bool) ([]byte, error)
- func String(s string) (string, error)
- func StringRestricted(s string, noUnset, noEmpty bool) (string, error)
- func StringRestrictedNoDigit(s string, noUnset, noEmpty bool, noDigit 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 BytesRestrictedNoDigit ¶ added in v1.4.0
Like BytesRestricted but additionally allows to ignore env variables which start with a digit.
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.
func ReadFileRestrictedNoDigit ¶ added in v1.4.0
func ReadFileRestrictedNoDigit(filename string, noUnset, noEmpty bool, noDigit bool) ([]byte, error)
Like ReadFileRestricted but additionally allows to ignore env variables which start with a digit.
func String ¶
String returns the parsed template string after processing it. If the parser encounters invalid input, it returns an error describing the failure.
func StringRestricted ¶
StringRestricted returns the parsed template string after processing it. If the parser encounters invalid input, or a restriction is violated, it returns an error describing the failure. Errors on first failure or returns a collection of failures if failOnFirst is false
Types ¶
This section is empty.
Source Files
Directories