Add support for environment variable to specify config file path (#858)

Author: aazon

README.md

@@ -125,6 +125,15 @@ default.
 #### Shell completion
 Check `jira completion --help` for more info on setting up a bash/zsh shell completion.
 
+#### Multiple projects
+
+The tool honors the `JIRA_CONFIG_FILE` environment variable, which specifies the location of the configuration file:
+
+```sh
+JIRA_CONFIG_FILE=./local_jira_config.yaml jira issue list 
+
+```
+
 ## Usage
 The tool currently comes with an issue, epic, and sprint explorer. The flags are [POSIX-compliant](https://www.gnu.org/software/libc/manual/html_node/Argument-Syntax.html).
 You can combine available flags in any order to create a unique query. For example, the command below will give you high priority issues created this month

internal/cmd/root/root.go

@@ -42,8 +42,13 @@ var (
 func init() {
 	cobra.OnInitialize(func() {
 		if config != "" {
+			// 1. Command line flag has the highest priority
 			viper.SetConfigFile(config)
+		} else if configFile := os.Getenv("JIRA_CONFIG_FILE"); configFile != "" {
+			// 2. Environment variable has second priority
+			viper.SetConfigFile(configFile)
 		} else {
+			// 3. Default location has the lowest priority
 			home, err := cmdutil.GetConfigHome()
 			if err != nil {
 				cmdutil.Failed("Error: %s", err)
@@ -98,7 +103,7 @@ func NewCmdRoot() *cobra.Command {
 
 	cmd.PersistentFlags().StringVarP(
 		&config, "config", "c", "",
-		fmt.Sprintf("Config file (default is %s/%s/%s.yml)", configHome, jiraConfig.Dir, jiraConfig.FileName),
+		fmt.Sprintf("Config file (default is %s/%s/%s.yml, can be overridden with JIRA_CONFIG_FILE env var)", configHome, jiraConfig.Dir, jiraConfig.FileName),
 	)
 	cmd.PersistentFlags().StringP(
 		"project", "p", "",