Git - Tips

28 Apr 2017

(how to) undo git reset HEAD~ or git --commit amend
(how to) fork a fork and sync it with original repo
(how to) remove file from Git
(how to) sign GitHub commits
(how to) use common configs in Git repo
(how to) show git diff output in pager
don’t use git-up gem
- set upstream
(how to) merge master into develop

(how to) undo `git reset HEAD~` or `git --commit amend`

$ git reset 'HEAD@{1}'

$ git reset ORIG_HEAD

when git commit --amend is undone, hash of the last commit is restored to its original value -> changes can be safely pushed to remote repo without --force option.

(how to) fork a fork and sync it with original repo

$ git clone <MY_FORK_REPO>
$ git remote -v
$ git remote add upstream <UPSTREAM_REPO>
$ git fetch upstream
$ git merge upstream/master
$ git mergetool

(how to) remove file from Git

https://stackoverflow.com/a/1143800/3632318

$ git rm --cached config/database.yml

(how to) sign GitHub commits

glossary

https://superuser.com/a/769488/326775

keypair consists of a private signing key and a public verification key
fingerprint is SHA-1 hash of the public key
GPG key ID is a part of the fingerprint:
- short key ID are the low 64 bits of the fingerprint
- long key ID are the low 128 bits of the fingerprint

for example:

$ gpg --list-keys --keyid-format LONG
/Users/tap/.gnupg/pubring.gpg
-----------------------------
pub   rsa4096/ACFDF508F789A2CB 2017-10-17 [SC]
      D9CA996601640B2121F29312ACFDF508F789A2CB
...

ACFDF508F789A2CB is a long GPG key ID
D9CA996601640B2121F29312ACFDF508F789A2CB is a fingerprint

official guides

use gpg --full-generate-key command to generate keypair - not gpg --gen-key command: the latter uses default key size of 2048 bits which can’t be changed.

$ZDOTDIR/.zshenv

add -S flag to git commit command in all aliases
export GPG_TTY environment variable
1. https://github.com/keybase/keybase-issues/issues/1712#issuecomment-141226705
this environment variable must be required for gpg-agent to work properly:

https://www.gnupg.org/documentation/manuals/gnupg/Invoking-GPG_002dAGENT.html

It is important that this environment variable (GPG_TTY) always reflects the output of the tty command.
```
# $ZDOTDIR/.zshenv

export GPG_TTY=$(tty)
```
Git will fail to sign commits if GPG_TTY is not set:
```
$ git commit -S -m 'foo'
error: gpg failed to sign the data
fatal: failed to write commit object
```

$ZDOTDIR/.zshrc

https://www.gnupg.org/documentation/manuals/gnupg/Invoking-GPG_002dAGENT.html

gpg-agent is a daemon to manage secret (private) keys independently from any protocol.

The agent is automatically started on demand by gpg, gpgsm, gpgconf, or gpg-connect-agent. Thus there is no reason to start it manually.

=> it’s not necessary to start gpg-agent manually (either via gpg-agent command or corresponding plugin provided by your plugin manager for Zsh).

~/.gnupg/gpg.conf

https://gist.github.com/bmhatfield/cc21ec0a3a2df963bffa3c1f884b676b

use-agent option

I thought it was the absence of this option that caused git commit command to hang before asking for the passphrase but in fact that hang was caused by trying to make commits from inside MacVim:
- I run :!publish command in MacVim
- pinentry prompts for the passphrase
- MacVim doesn’t allow to enter the passphrase since all commands run in a non-interactive shell by default
- I cancel command with <C-c>
- pinentry still waits for the passphrase in the background (correspoding process having a very high CPU usage)
- I cannot make a commit from the command line because pinentry is still busy waiting for the passphrase
TL;DR: use-agent option can be safely removed from gpg.conf.
passphrase-file and pinentry-mode options
1. https://github.com/keybase/keybase-issues/issues/1712#issuecomment-141226705
use these options to read passphrase from file instead of typing it manually - it’s especially useful when running git commit command in a non-interactive shell (say, from inside MacVim):
```
# ~/.gnupg/gpg.conf

passphrase-file /Users/tap/.gnupg/passphrase
pinentry-mode loopback
```
don’t use tilde in passphrase file path - or else:
```
$ git commit -S -m "foo"
error: gpg failed to sign the data
fatal: failed to write commit object
```
if pinentry-mode loopback option is missing passphrase won’t be read from file at all - you’ll have to enter it manually then (even though passphrase file is specified).
batch option

this option is supposed to be used along with passphrase-file option but it all works as is so the former can be omitted.

~/.gitconfig

set commit email (required)
```
$ git config --global user.email GITHUB_VERIFIED_EMAIL
```
if Git email doesn’t match GitHub email, commit will have Unverified badge on GitHub.
set signing key (optional)
1. https://stackoverflow.com/questions/41052538/git-error-gpg-failed-to-sign-data
```
$ git config --global user.signingkey GPG_KEY_ID
```
I guess, setting signing key explicitly might be required if you have more than one signing key.

(how to) use common configs in Git repo

just use hardlinks instead of symlinks - they are commited to Git repo like ordinary files.

UPDATE

still it’s not possible: at some point (most likely, when hardlinked file is changed in upstream) hardlink and original file no longer share the same inode so fetched changes are not reflected in original file.

(how to) show `git diff` output in pager

https://superuser.com/questions/366930/how-do-i-get-the-git-pager-to-clean-up-screen-output-after-exit#comment2040311_1202694

  ; ~/.gitconfig

  [core]
    ; ...
+   pager = less -+X -+F

don’t use git-up gem

https://github.com/aanand/git-up

https://github.com/aanand/git-up#warning

This project is no longer maintained, for several reasons:

As of Git 2.9, git pull –rebase –autostash does basically the same thing.

=> add Git alias instead:

in Git config directly

  # ~/.gitconfig

  [alias]
+   # https://github.com/aanand/git-up
+   up = pull --rebase --autostash

or using git config command

$ git config --global alias.up 'pull --rebase --autostash'

set upstream

Git - Notes

see the linked post for details on how and why it’s necessary to set upstream for your branch - git-up gem would handle it for us before but now we should do it by ourselves.

(how to) merge master into develop

$ git checkout develop
$ git merge master
$ git mergetool
$ git commit -m "merge master"
$ git push

NOTE: it’s important to create and push commit even if there are no changes when all conflicts are resolved (git status displays a message that working tree is clean).

tap349