NBash

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#!/bin/sh
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# An example hook script to update a checked-out tree on a git push.
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#
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# This hook is invoked by git-receive-pack(1) when it reacts to git
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# push and updates reference(s) in its repository, and when the push
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# tries to update the branch that is currently checked out and the
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# receive.denyCurrentBranch configuration variable is set to
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# updateInstead.
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#
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# By default, such a push is refused if the working tree and the index
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# of the remote repository has any difference from the currently
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# checked out commit; when both the working tree and the index match
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# the current commit, they are updated to match the newly pushed tip
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# of the branch. This hook is to be used to override the default
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# behaviour; however the code below reimplements the default behaviour
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# as a starting point for convenient modification.
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#
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# The hook receives the commit with which the tip of the current
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# branch is going to be updated:
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commit=$1
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# It can exit with a non-zero status to refuse the push (when it does
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# so, it must not modify the index or the working tree).
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die () {
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	echo >&2 "$*"
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	exit 1
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}
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# Or it can make any necessary changes to the working tree and to the
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# index to bring them to the desired state when the tip of the current
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# branch is updated to the new commit, and exit with a zero status.
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#
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# For example, the hook can simply run git read-tree -u -m HEAD "$1"
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# in order to emulate git fetch that is run in the reverse direction
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# with git push, as the two-tree form of git read-tree -u -m is
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# essentially the same as git switch or git checkout that switches
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# branches while keeping the local changes in the working tree that do
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# not interfere with the difference between the branches.
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# The below is a more-or-less exact translation to shell of the C code
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# for the default behaviour for git's push-to-checkout hook defined in
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# the push_to_deploy() function in builtin/receive-pack.c.
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#
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# Note that the hook will be executed from the repository directory,
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# not from the working tree, so if you want to perform operations on
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# the working tree, you will have to adapt your code accordingly, e.g.
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# by adding "cd .." or using relative paths.
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if ! git update-index -q --ignore-submodules --refresh
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then
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	die "Up-to-date check failed"
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fi
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if ! git diff-files --quiet --ignore-submodules --
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then
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	die "Working directory has unstaged changes"
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fi
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# This is a rough translation of:
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#
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#   head_has_history() ? "HEAD" : EMPTY_TREE_SHA1_HEX
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if git cat-file -e HEAD 2>/dev/null
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then
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	head=HEAD
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else
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	head=$(git hash-object -t tree --stdin </dev/null)
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fi
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if ! git diff-index --quiet --cached --ignore-submodules $head --
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then
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	die "Working directory has staged changes"
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fi
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if ! git read-tree -u -m "$commit"
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then
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	die "Could not update working tree to new HEAD"
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fi
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