GPG key and agent for Git commit signing

.gpg with agent for Git commit signing

This is working mix of information found on the Internet.
Most tutorials mention obsolete --write-env-file,
so I use simple eval with whole output redirected to /dev/null
in order to silently spawn GPG agent daemon.

Had to use test command mentioned above so GPG asked for key's passphrase (only once).

Got this working on:

- Kubuntu 16.04
- gpg (GnuPG) 1.4.20
- gpg (GnuPG) 2.1.11
- zsh 5.1.1 (x86_64-ubuntu-linux-gnu)

Works with PhpStorm (built-in Git support) and GitExtensions (through Mono).

CLI command for testing agent:
echo "test" | gpg --use-agent -ase -r <YOUR_KEY_ID> | gpg --use-agent
echo "test" | gpg2 --use-agent -ase -r <YOUR_KEY_ID> | gpg2 --use-agent

gpg-agent.conf

# ~/.gnupg/gpg-agent.conf

default-cache-ttl 28800
max-cache-ttl 28800

gpg.conf

# ~/.gnupg/gpg.conf

keyserver-options auto-key-retrieve
no-tty
use-agent

default-key  <YOUR_KEY_ID>

zshrc

# ~/.zshrc

# Make sure GPG Agent is working
if test -f ~/.gpg-agent-info && \
    kill -0 `cut -d: -f 2 ~/.gpg-agent-info` 2>/dev/null; then
    export GPG_AGENT_INFO=`cat ~/.gpg-agent-info | cut -c 16-`
else
    eval "$(gpg-agent --daemon --no-grab > /dev/null 2>&1)"
fi
export GPG_TTY=$(tty)
export GPG_AGENT_INFO
export GPGKEY=<YOUR_KEY_ID>