Prerequisites

xbar
Recent version of Golang

tl;dr installation instructions

Install xbar.
Copy the gmailnotifier.*.cgo executable from the plugins directory of this github repo to a local directory on your Mac.
Create the .creds_gmail file in the same local directory, this file stores the email|password credentials, with the username and gmail app passwords separated by a pipe.

Detailed installation instructions

xbar installation

Get the most recent release of xbar from https://github.com/matryer/xbar/releases
Download and run the most recent xbar.vX.Y.Z.dmg osx installer
Launch the xbar app. For example, using Spotlight (Command + Space), type in xbar and you should see the application listed. Launch it, then click Open to install it.

You may need to go to System Preferences -> Security & Privacy -> General and allow the app to be opened. This step applies to installing gmailnotifier too, because these are third party apps, not ones from the Mac app store.
You will be prompted to choose a location where the plugins are located. For now, you can cancel out of this, we'll set that location once gmailnotifier is installed.

gmailnotifier installation

Download the most recent release from https://github.com/bricklen/gmailnotifier/releases
Extract the zip file (or tarball). If you're unsure where to extract to, create a directory under $HOME called apps and extract the zip file there.
Launch the xbar app if you haven't already.
Click on the xbar text/icon in the toolbar, select Change Plugin Folder, then set the plugins directory location to where your toolbar apps will run from. This should be gmailnotifier-X.Y/plugins, where X.Y is the version. (see NOTE below for alternatives).

You can change this plugins setting at any time by clicking on your xbar toolbar app, then clicking Preferences -> Change Plugin Folder.

NOTE: If you only want to run this app (and no other xbar plugins), using the gmailnotifier-X.Y/plugins directory is fine. However, if you have other plugins, you probably want a plugins directory in a more central location (eg. $HOME/xbar/plugins/. If you do use an external xbar plugins directory, you will need to copy the gmailnotifier.*.cgo executable to that plugins directory.
If you get a warning like "gmailnotifier.30s.cgo cannot be opened because the developer cannot be verified", you will need go to System Preferences -> Security & Privacy -> General and allow the app to be opened.
If you needed to grant permission to install the gmailnotifier app, repeat the earlier xbar Change Plugin Folder step (step #4)
Once gmailnotifier is successfully installed, add a file called .creds_gmail to same location as the executable (eg. gmailnotifier-X.Y/plugins/). This file MUST exist for the plugin to know which accounts to check.

Add the Gmail username and app password to .creds_gmail separated by a pipe (|).

Do this for each email account you want to check, one username|app-password pair per line.

Example
```
examplename|mysecretpassword
myotheremail|supersecretpass
my-gsuite-email@acme.com|myuncrackablepasswd
```
Click the xbar icon in your toolbar, select Preferences -> Refresh All.
Your plugin should now show as a small mail icon with the number of unread emails to the right of it.

Note about G-Suite (non-gmail) domains

This plugin works for those, but you will need to supply your full organization address as your username, whereas if it is for a regular Gmail account, you only need to supply your username.

Directory layout

gmailnotifier-X.Y
├── .gitignore
├── LICENSE
├── README.md
├── plugins
│   ├── .creds_gmail
│   └── gmailnotifier.30s.cgo
└── src
    └── main.go

Rebuilding the Golang executable

If you make changes to main.go, you will need to rebuild the .cgo executable file.

From the gmailnotifier-X.Y directory, build the executable:

go build -o plugins/gmailnotifier.30s.cgo src/main.go

Other options for the plugin

The official guide is at https://github.com/matryer/xbar-plugins/blob/main/CONTRIBUTING.md

Changing the execution intervals

The notifier check frequency is defined by the interval in the file name (between the name and extension). For example, to check every 30 seconds, the file name would be gmailnotifier.30s.cgo

About the credentials file

If you fork or build from source, be sure to maintain the credentials file name of .creds_gmail, or if you change it, make sure to update the .gitignore file with the new creds file name so that it does not get inadvertently committed to your github repo. If you end up exposing usernames and passwords in a github repo you're going to be in for a bad time.

Use Gmail App Passwords instead of your login password

It is strongly recommend using App Passwords instead of your login password, as they make it easy to have a separate password for each application that needs to connect to your gmail account, and you can revoke them individually if required. See https://support.google.com/accounts/answer/185833?hl=en

Excerpt

When you use 2-Step Verification, some apps or devices may be blocked from accessing your Google Account. App Passwords are a way to let the blocked app or device access your Google Account.

Privacy notice

This app does not save, nor send your credentials (or anything else for that matter) anywhere, except directly to https://mail.google.com/mail to get the unread mail counts.

You are encouraged to review the main.go source file - and to build a new executable from that - if you have any concerns about the code.

Disclaimer

See the LICENSE about disclaimers of liability. As with all Open Source software: use at your own risk.

TODO

Investigate rewriting this script to use the Google native API tools, https://godoc.org/google.golang.org/api/gmail/
Add option to delete a message. Prompt to confirm.

bricklen / gmailnotifier