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Helpful Git Commands

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mocleiri edited this page Jan 20, 2011 · 8 revisions

Helpful Git Commands

This page contains useful git commands.

Get back the previous version of a file that has been deleted.

In Jan 2011 we deleted all of the hidden eclipse files from the repository and added them into the /.gitignore file.

So the idea is that those files can be generated automatically by the tool. However if local devs need to retrieve the original (last committed value version) this is the command to do it:


git show SHA-1:<full repository path>

The show command can show a specific file from a previous commit. And the standard labels of HEAD and HEAD^ ( for 1 commit before the current head) work:

git checkout core-1.4.x

cd jdk-1.5-parent/ddcalendar-parent/ddcalendar-examples

git show HEAD^:jdk-1.5-parent/ddcalendar-parent/ddcalendar-examples/.project > .project

Identify which files were deleted on each commit

The git log --diff-filter=D can be used to show the commits backward in time from the current HEAD where a file was deleted.

The --name-only option can be used to show the file names that were deleted for each commit

git log --format=oneline --diff-filter=D --name-only

8f3e43a68816772f3ba6b696ca768c063cdb94d0 push code cleanup
jdk-1.6-parent/push-parent-jdk-1.6/README

Here we can see that with commit 8f3e43a the file was deleted. There for it existed in the previous commit (8f3e43a^) and we can show the content like this:

git show 8f3e43a68816772f3ba6b696ca768c063cdb94d0^:jdk-1.6-parent/push-parent-jdk-1.6/README

A clone of wicketstuff-core/push-parent project.
The aim is to upgrade it to latest Cometd and Jetty versions.

Port Features from core-1.4.x into master

As we get started with 1.5 releases much of the content in the master branch is from when the branch was originally split from the core-1.4.x branch.

Since most development has occurred on the core-1.4.x branch it is likely to be common that we want to merge the changes from the core-1.4.x branch back into master.

Approach:

  • Create a new project-1.4.x branch from core-1.4.x

  • Use git filter-branch --subdirectory-filter jdk-1.5-parent/module to create a new branch containing only the module files.

  • Switch back to master and use a subtree merge to merge the core-1.4.x module on top of the existing 1.5 module.

  • Commit everything as a squashed commit.

The only downside to this approach is that the filter-branch process creates new commits so if the end result is not squashed together it might not make sense.

In depth steps

$ git checkout core-1.4.x

$ git checkout -b jasperreports-parent-1.4.x core-1.4.x

$ git filter-branch --subdirectory-filter jdk-1.5-parent/jasperreports-parent

$ git ls-tree jasperreports-parent-1.4.x
100644 blob 54ca1ea045a5259f66be37ce28bf6d53a2ffd5fd    .cvsignore
100644 blob d9a10c0d8e868ebf8da0b3dc95bb0be634c34bfe    LICENSE.txt
040000 tree 43cedd6d3f165f4361e61f0451f7fd539e729d07    jasperreports-examples
040000 tree 42ecc877c2024ad25ff3025a811e456f3386d107    jasperreports
040000 tree 6ddeb41e46e8d1daa9e8516ed9ae030686be752e    licenses
100644 blob 05c303f26465dc24f0ffcf4bce1709ad9d9f8961    pom.xml
040000 tree a90503204708143e3e0914d9bbbb78ac18f44fbc    xdocs

$ git checkout master
  • From the root directory run the merge command git merge -s subtree --squash --no-commit jasperreports-parent-1.4.x.
$ git status
# On branch master
# Changes to be committed:
#   (use "git reset HEAD <file>..." to unstage)
#
#       new file:   jdk-1.5-parent/jasperreports-parent/.cvsignore
#       modified:   jdk-1.5-parent/jasperreports-parent/jasperreports-examples/pom.xml
#       modified:   jdk-1.5-parent/jasperreports-parent/jasperreports/pom.xml
#       modified:   jdk-1.5-parent/jasperreports-parent/jasperreports/src/main/java/org/
wicketstuff/jasperreports/EmbeddedJRReport.java
#       modified:   jdk-1.5-parent/jasperreports-parent/jasperreports/src/main/java/org/
wicketstuff/jasperreports/JRConcreteResource.java
#       modified:   jdk-1.5-parent/jasperreports-parent/jasperreports/src/main/java/org/
wicketstuff/jasperreports/JRImageResource.java
#       modified:   jdk-1.5-parent/jasperreports-parent/jasperreports/src/main/java/org/
wicketstuff/jasperreports/JRResource.java
#       modified:   jdk-1.5-parent/jasperreports-parent/pom.xml

  • Note that the pom's have changed back to 1.4-SNAPSHOT so you will have to change them back to 1.5-SNAPSHOT

  • After making the changes to the pom.xml's you can commit the merge git commit. Write a single commit message to represent the changes merged in from the core-1.4.x branch. Build up a description based on the squashed commits that make up the initial message.

Reverting a commit

If you committed something that is wrong to a public branch the only way to undo it is to create a new commit that undoes the damage.

Steps:

  • You get the SHA1 of the commit that was made in error.

  • You run git revert <SHA1> and then if there are conflicts resolve them with git mergetool.

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