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Patrick McKenna
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A selection of:
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how to's
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general advice for working with Git
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Assumptions:
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You're comfortable with command line Git
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You understand the basics of Git's internals
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You're familiar with the basics of shell scripting
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Assumptions:
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You're comfortable with command line Git
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You understand the basics of Git's internals
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You're familiar with the basics of shell scripting
Note: examples checked on Git 2.11.0
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For example:
What commits were added to <branch> by my last pull?
--
git-show-new <branch>template: content
First, we need accept a <branch> arg
--
... and provide a sensible default if none supplied
--
#!/bin/bash
if [ $1 ]; then
branch="$1"
else
branch="HEAD"
fi
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Next: generate the list of new commits
--
Use git rev-list
--
It generates and traverses commit graphs
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General syntax for commits reachable from A but not B:
--
git rev-list A ^B--
(A, B are commit-ish)
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General syntax for commits reachable from A but not B:
git rev-list A ^BCould use alternate sytax...
git rev-list B..Atemplate: content
git rev-list A ^B--
In our case:
Ais the commit to which<branch>currently points
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git rev-list A ^BIn our case:
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Ais the commit to which<branch>currently points -
Bis the commit<branch>pointed to before our latestpull
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How do we specify the commit <branch> used to point to?
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Using @{<n>} syntax:
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<branch>@{<n>}--
Gets the nth prior value of <branch>
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Hence:
git rev-list <branch> ^<branch>@{1}template: content
A final version might look like this:
#!/bin/bash
if [ $1 ]; then
branch="$1"
else
branch="HEAD"
fi
printf "\n%s%s\n\n" $(git rev-list $branch ^$branch@{1} | wc -l) \
" commits were added by your last update to $branch:"
git --no-pager log $branch ^$branch@{1} --onelinetemplate: content
--
Be careful with Git's "convenience" syntax, e.g.@
--
BASE=$(git merge-base @ @{u} 2>/dev/null || echo "none")--
What are those @ symbols?!
--
Those are the Unicode code points for the "the Git command line was getting too comprehensible" character in Swahili
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BASE=$(git merge-base @ @{u} 2>/dev/null || echo "none")--
- the
@is short forHEAD
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BASE=$(git merge-base @ @{u} 2>/dev/null || echo "none")-
the
@is short forHEAD -
@{u}is short for@{upstream}
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BASE=$(git merge-base @ @{u} 2>/dev/null || echo "none")-
the
@is short forHEAD -
@{u}is short for@{upstream}
Using that in scripting is a terrible idea, IMHO.
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Git can be tricky enough as is
--
Make scripts reader-friendly where possible
--
-BASE=$(git merge-base @ @{u} 2>/dev/null || echo "none")
+BASE=$(git merge-base HEAD @{upstream} 2>/dev/null || echo "none")template: section
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- add branch metadata
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add branch metadata
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using exclude patterns in scripts
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--
How:
git branch --edit-description <branch>--
Data written to .git/config
--
- follows renames
- deleted when
<branch>deleted
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.git/config meant to be extensible for third party uses
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Ex: testing scripts that respect contents of:
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.gitignore -
.git/info/exclude
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Re-implementing Git exclude patterns non-trivial
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Re-implementing Git exclude patterns non-trivial
Essential plumbing command:
git check-ignore <pathname>--
Returns <pathname> if it matches an exclude pattern
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git check-ignore <pathname>template: content
git check-ignore <pathname>- no recursive option for wildcard searches
--
# assume .gitignore includes the pattern: *sample.py
> git check-ignore plugins/*
# output would include
# plugins/basic_sample.py
# output would not include
# plugins/operators/basic_sample.pytemplate: content
git check-ignore <pathname>-
no recursive option for wildcard searches
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can't filter against custom ignore file
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git check-ignore <pathname>-
no recursive option for wildcard searches
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can't filter against custom ignore file
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not listed on
git-scm.com/docs(but it's there)
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First and third issues can solved:
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git ls-files --others <pathname(s)>--
Shows untracked files
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Ex: pre-commit hook to do Python linting
--
# in .git/hooks/pre-commit
python_dirs= #...
pep8 \
--exclude $(git ls-files --others $python_dirs | tr '\n', ',') \
$python_dirstemplate: section
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2 separate repos, each with history
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Import <subdir> from <source-repo> into <target-repo>
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(and preserve history of <subdir>)
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# before
.<source-repo> .<target-repo>
|-- src |-- src
|-- bin |-- bin
|-- <subdir>
# after
.<source-repo> .<target-repo>
|-- src |-- src
|-- bin |-- bin
|-- <subdir>template: content
- a one-time operation -> submodules inappropriate
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a one-time operation, so submodules inappropriate
- e.g. split apart a large project
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a one-time operation -> submodules inappropriate
- e.g. split apart large project
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assume
<subdir>does not exist in<target-repo>, and that we want to use the same name
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Step 1: construct a "synthetic" history
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(all commits in <source-repo> that touch files in <subdir>)
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In <source-repo>:
git subtree split --branch <branch> --prefix <subdir>template: content
git subtree split --branch <branch> --prefix <subdir>template: content
git subtree split --branch <branch> --prefix <subdir>- creates a new branch
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git subtree split --branch <branch> --prefix <subdir>- creates a new branch
- synthesizes commit history
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git subtree split --branch <branch> --prefix <subdir>- creates a new branch
- synthesizes commit history
- each commit has contents of
<subdir>at root of project - repeated splits produce identical histories
- each commit has contents of
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Step 2: get contents of <subdir> into <target-repo>:
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In <target-repo>:
git subtree add --prefix <subdir> <source-repo> <branch>template: content
git subtree add --prefix <subdir> <source-repo> <branch>--
- imports synthetic history, puts contents into
<subdir>
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Done...with some caveats
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git log may not work as you expect
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Look at the history of a given<file> in <subdir>:
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In <target-repo>:
>>> git log -- <subdir>/<file>
commit 2e259f35fea13ca6bbfb8bd33be6476caea5cc86
Merge: e6a4851 d0e7410
Add '<subdir>' from commit 'd0e74107e4517e48888b3de5bd7b129bc12a041f'
git-subtree-dir: <subdir>
git-subtree-mainline: e6a4851ca13c9fa76fd25277b1d1bb6cd7e61519
git-subtree-split: d0e74107e4517e48888b3de5bd7b129bc12a041f
>>>--
Only 1 commit—didn't we import the full history?
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Adding --follow doesn't help
--
There's a workaround:
--
git log -- *<file>--
But limitations to this
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In <target-repo>:
--
git checkout -b <branch>template: content
In <target-repo>:
git checkout -b <branch>
git remote add -f <remote-name> <source-repo>template: content
In <target-repo>:
git checkout -b <branch>
git remote add -f <remote-name> <source-repo>
git merge --allow-unrelated-histories <remote-name>/<branch>--
git log -- <pathname> should now work as expected
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filter-branch generalizes better (to processing all branches)...
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... but it is notoriously tricky to use
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subtree simpler...
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... but it lives in /contrib (while filter-branch ships with Git)
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git checkout --orphanto create new branch w/o parents, disconnected from all history
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git checkout --orphanto create new branch w/o parents, disconnected from all history -
for an abbreviated history, try
filter-branchwith grafts
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- Git doesn't have any notion of "this commit was made on this branch"
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- Git doesn't have any notion of "this commit was made on this branch"
- Git won't expand built-in commands used as aliases
- was debated, a case of Git not wanting to let people hurt themselves(!)
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- Git doesn't have any notion of "this commit was made on this branch"
- Git won't expand built-in commands used as aliases
- was debated, a case of Git not wanting to let people hurt themselves(!)
- consider
git-sh-setup.sh"scriplet"
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- Git doesn't have any notion of "this commit was made on this branch"
- Git won't expand built-in commands used as aliases
- was debated, a case of Git not wanting to let people hurt themselves(!)
- consider
git-sh-setup.sh"scriplet" - contribute to Git:
submitgit.herokuapp.com
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- Git doesn't have any notion of "this commit was made on this branch"
- Git won't expand built-in commands used as aliases
- was debated, a case of Git not wanting to let people hurt themselves(!)
- consider
git-sh-setup.sh"scriplet" - contribute to Git:
submitgit.herokuapp.com - reduce merge conflict pain:
github.com/mhagger/git-imerge
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Patrick McKenna