README
¶
Interpolate
A Go library for parameter expansion (like ${NAME} or $NAME) in strings from environment
variables. An implementation of POSIX Parameter
Expansion,
plus some other basic operations that you'd expect in a shell scripting environment like
bash.
Installation
go get github.com/mfridman/interpolate@latest
Usage
package main
import (
"github.com/mfridman/interpolate"
"fmt"
)
func main() {
env := interpolate.NewSliceEnv([]string{
"NAME=James",
})
output, _ := interpolate.Interpolate(env, "Hello... ${NAME} welcome to the ${ANOTHER_VAR:-🏖}")
fmt.Println(output)
// Output: Hello... James welcome to the 🏖
}
Supported Expansions
-
${parameter}or$parameter- Use value. If parameter is set, then it shall be substituted; otherwise, it will be blank
-
${parameter:-[word]}- Use default values. If parameter is unset or null, the expansion of word (or an empty string if word is omitted) shall be substituted; otherwise, the value of parameter shall be substituted.
-
${parameter-[word]}- Use default values when not set. If parameter is unset, the expansion of word (or an empty string if word is omitted) shall be substituted; otherwise, the value of parameter shall be substituted.
-
${parameter:[offset]}- Use the substring of parameter after offset. A negative offset must be separated from the colon with a space, and will select from the end of the string. If the value is out of bounds, an empty string will be substituted.
-
${parameter:[offset]:[length]}- Use the substring of parameter after offset of given length. A negative offset must be separated from the colon with a space, and will select from the end of the string. If the offset is out of bounds, an empty string will be substituted. If the length is greater than the length then the entire string will be returned.
-
${parameter:?[word]}- Indicate Error if Null or Unset. If parameter is unset or null, the expansion of word (or a message indicating it is unset if word is omitted) shall be returned as an error.
Prior work
This repository is a fork of buildkite/interpolate. I'd like to thank the authors of that library for their work. I've forked it to make some changes that I needed for my own use cases, and to make it easier to maintain. I've also added some tests and documentation.
License
Licensed under MIT license, in LICENSE.
Documentation
¶
Index ¶
Examples ¶
Constants ¶
This section is empty.
Variables ¶
This section is empty.
Functions ¶
func Identifiers ¶
Indentifiers parses the identifiers from any expansions in the provided string
func Interpolate ¶
Interpolate takes a set of environment and interpolates it into the provided string using shell script expansions
Example ¶
package main
import (
"fmt"
"log"
"github.com/mfridman/interpolate"
)
func main() {
env := interpolate.NewSliceEnv([]string{
"NAME=James",
})
output, err := interpolate.Interpolate(env, "Hello... ${NAME} welcome to the ${ANOTHER_VAR:-🏖}")
if err != nil {
log.Fatal(err)
}
fmt.Println(output)
}
Output: Hello... James welcome to the 🏖
Types ¶
type EmptyValueExpansion ¶
type EmptyValueExpansion struct {
Identifier string
Content Expression
}
EmptyValueExpansion returns either the value of an env, or a default value if it's unset or null
func (EmptyValueExpansion) Identifiers ¶
func (e EmptyValueExpansion) Identifiers() []string
type Env ¶
Env is an interface for getting environment variables by name and returning a boolean indicating whether the variable was found.
func NewSliceEnv ¶
NewSliceEnv creates an Env from a slice of environment variables in the form "key=value".
This can be used with os.Environ to create an Env.
type Expression ¶
type Expression []ExpressionItem
Expression is a collection of either Text or Expansions
func (Expression) Identifiers ¶
func (e Expression) Identifiers() []string
type ExpressionItem ¶
ExpressionItem models either an Expansion or Text. Either/Or, never both.
func (ExpressionItem) String ¶
func (i ExpressionItem) String() string
type Parser ¶
type Parser struct {
// contains filtered or unexported fields
}
Parser takes a string and parses out a tree of structs that represent text and Expansions
func (*Parser) Parse ¶
func (p *Parser) Parse() (Expression, error)
Parse expansions out of the internal text and return them as a tree of Expressions
type RequiredExpansion ¶
type RequiredExpansion struct {
Identifier string
Message Expression
}
RequiredExpansion returns an env value, or an error if it is unset
func (RequiredExpansion) Identifiers ¶
func (e RequiredExpansion) Identifiers() []string
type SubstringExpansion ¶
SubstringExpansion returns a substring (or slice) of the env
func (SubstringExpansion) Identifiers ¶
func (e SubstringExpansion) Identifiers() []string
type UnsetValueExpansion ¶
type UnsetValueExpansion struct {
Identifier string
Content Expression
}
UnsetValueExpansion returns either the value of an env, or a default value if it's unset
func (UnsetValueExpansion) Identifiers ¶
func (e UnsetValueExpansion) Identifiers() []string
type VariableExpansion ¶
type VariableExpansion struct {
Identifier string
}
VariableExpansion represents either $VAR or ${VAR}, our simplest expansion
func (VariableExpansion) Identifiers ¶
func (e VariableExpansion) Identifiers() []string
Source Files