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Package properties provides functions for reading and writing ISO-8859-1 and UTF-8 encoded .properties files and has support for recursive property expansion. Java properties files are ISO-8859-1 encoded and use Unicode literals for characters outside the ISO character set. Unicode literals can be used in UTF-8 encoded properties files but aren't necessary. To load a single properties file use MustLoadFile(): To load multiple properties files use MustLoadFiles() which loads the files in the given order and merges the result. Missing properties files can be ignored if the 'ignoreMissing' flag is set to true. Filenames can contain environment variables which are expanded before loading. All of the different key/value delimiters ' ', ':' and '=' are supported as well as the comment characters '!' and '#' and multi-line values. Properties stores all comments preceding a key and provides GetComments() and SetComments() methods to retrieve and update them. The convenience functions GetComment() and SetComment() allow access to the last comment. The WriteComment() method writes properties files including the comments and with the keys in the original order. This can be used for sanitizing properties files. Property expansion is recursive and circular references and malformed expressions are not allowed and cause an error. Expansion of environment variables is supported. The default property expansion format is ${key} but can be changed by setting different pre- and postfix values on the Properties object. Properties provides convenience functions for getting typed values with default values if the key does not exist or the type conversion failed. As an alternative properties may be applied with the standard library's flag implementation at any time. Properties provides several MustXXX() convenience functions which will terminate the app if an error occurs. The behavior of the failure is configurable and the default is to call log.Fatal(err). To have the MustXXX() functions panic instead of logging the error set a different ErrorHandler before you use the Properties package. You can also provide your own ErrorHandler function. The only requirement is that the error handler function must exit after handling the error. Properties can also be loaded into a struct via the `Decode` method, e.g. See `Decode()` method for the full documentation. The following documents provide a description of the properties file format.


Version published


[![Travis CI Status](](

# Overview

#### Please run `git pull --tags` to update the tags. See [below](#updated-git-tags) why.

properties is a Go library for reading and writing properties files.

It supports reading from multiple files or URLs and Spring style recursive
property expansion of expressions like `${key}` to their corresponding value.
Value expressions can refer to other keys like in `${key}` or to environment
variables like in `${USER}`.  Filenames can also contain environment variables
like in `/home/${USER}/`.

Properties can be decoded into structs, maps, arrays and values through
struct tags.

Comments and the order of keys are preserved. Comments can be modified
and can be written to the output.

The properties library supports both ISO-8859-1 and UTF-8 encoded data.

Starting from version 1.3.0 the behavior of the MustXXX() functions is
configurable by providing a custom `ErrorHandler` function. The default has
changed from `panic` to `log.Fatal` but this is configurable and custom
error handling functions can be provided. See the package documentation for

Read the full documentation on [![GoDoc](](

## Getting Started

import (

func main() {
	// init from a file
	p := properties.MustLoadFile("${HOME}/", properties.UTF8)

	// or multiple files
	p = properties.MustLoadFiles([]string{
		}, properties.UTF8, true)

	// or from a map
	p = properties.LoadMap(map[string]string{"key": "value", "abc": "def"})

	// or from a string
	p = properties.MustLoadString("key=value\nabc=def")

	// or from a URL
	p = properties.MustLoadURL("http://host/path")

	// or from multiple URLs
	p = properties.MustLoadURL([]string{
		}, true)

	// or from flags

	// get values through getters
	host := p.MustGetString("host")
	port := p.GetInt("port", 8080)

	// or through Decode
	type Config struct {
		Host    string        `properties:"host"`
		Port    int           `properties:"port,default=9000"`
		Accept  []string      `properties:"accept,default=image/png;image;gif"`
		Timeout time.Duration `properties:"timeout,default=5s"`
	var cfg Config
	if err := p.Decode(&cfg); err != nil {


## Installation and Upgrade

$ go get -u

## License

2 clause BSD license. See [LICENSE]( file for details.

## ToDo

* Dump contents with passwords and secrets obscured

## Updated Git tags

#### 13 Feb 2018

I realized that all of the git tags I had pushed before v1.7.5 were lightweight tags
and I've only recently learned that this doesn't play well with `git describe` 😞

I have replaced all lightweight tags with signed tags using this script which should
retain the commit date, name and email address. Please run `git pull --tags` to update them.

Worst case you have to reclone the repo.

echo "Updating $tag"
date=$(git show ${tag}^0 --format=%aD | head -1)
email=$(git show ${tag}^0 --format=%aE | head -1)
name=$(git show ${tag}^0 --format=%aN | head -1)
GIT_COMMITTER_DATE="$date" GIT_COMMITTER_NAME="$name" GIT_COMMITTER_EMAIL="$email" git tag -s -f ${tag} ${tag}^0 -m ${tag}

I apologize for the inconvenience.



Last updated on 08 Dec 2022

Did you know?

Socket installs a GitHub app to automatically flag issues on every pull request and report the health of your dependencies. Find out what is inside your node modules and prevent malicious activity before you update the dependencies.


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