Advanced Git - Functionality and Features

Advanced Git - Functionality and Features

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  2 © 2018 BrentLaster@BrentCLaster 2 Advanced Git: Functionality and Features All Things Open 2019 Brent Laster
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  3 © 2018 BrentLaster@BrentCLaster 3 @BrentCLaster About me § Director, R&D § Global trainer – training (Git, Jenkins, Gradle, Gerriit, Continuous Pipelines) § Author - § OpenSource.com § Professional Git book § Jenkins 2 – Up and Running book § Continuous Integration vs. Continuous Delivery vs. Continuous Deployment mini-book on Safari § https://www.linkedin.com/in/brentlaster § @BrentCLaster
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  4 © 2018 BrentLaster@BrentCLaster 4 @BrentCLaster Book – Professional Git § Extensive Git reference, explanations, and examples § First part for non-technical § Beginner and advanced reference § Hands-on labs
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  5 © 2018 BrentLaster@BrentCLaster 5 @BrentCLaster Jenkins 2 Book § Jenkins 2 – Up and Running § Deployment pipeline automation as code § “It’s an ideal book for those who are new to CI/CD, as well as those who have been using Jenkins for many years. This book will help you discover and rediscover Jenkins.” By Kohsuke Kawaguchi, Creator of Jenkins
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  6 © 2018 BrentLaster@BrentCLaster 6 @BrentCLaster Agenda § Core concepts refresh § Merging and Rebasing § Stash § Reset and Revert § Rerere § Bisect § Worktrees § Subtrees § Interactive Rebase § Notes § Grep
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  7 © 2018 BrentLaster@BrentCLaster Check Out Commit C h e c k o u t C o m m i t Clone Remote Repository Local Environment Central Server Local Machine Centralized Version Control Model Distributed Version Control Model Centralized vs. Distributed VCS
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  8 © 2018 BrentLaster@BrentCLaster 8 @BrentCLaster Git in One Picture Staging Area Remote Repository Local Repository Working Directory P u l l Dev Prod Public Test C h e c k o u t Server Add Commit Push Clone Local Machine F e t c h
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  9 © 2018 BrentLaster@BrentCLaster 9 @BrentCLaster Git Granularity (What is a unit?) § In traditional source control, the unit of granularity is usually a file § In Git, the unit of granularity is usually a tree dir: proj1 file1.java file2.java Working directory file1.java CVS GitCommit file1.java Delta Commit Snapshot
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  10 © 2018 BrentLaster@BrentCLaster 10 @BrentCLaster Merging: What is a Fast-forward? § Assume you have three branches as below § You want to merge hotfix into master (so master will have your hotfix for future development) $ git checkout master $ git merge hotfix Updating f42c576..3a0874c Fast Forward README | 1- 1 files changed, 0 insertions(+) 1 deletions (-) About “Fast Forward” – because commit pointed to by branch merged was directly “upstream” of the current commit, Git moves the pointer forward (Both branches were in the same line of development, so the net result is that master and hotfix point to the same commit) C2 C3 C0 C1 C4 feature hotfix
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  11 © 2018 BrentLaster@BrentCLaster 11 @BrentCLaster Merging: What is a 3-way Merge? § Assume branching scenario below § master and feature branches have both diverged (changed) since their last common ancestor (commit/snapshot) § Intent is to change to master and merge in feature § Current commit on target branch isn’t a direct ancestor of current commit on branch you’re merging in (i.e. C4 isn’t on the same line of development as C5) § Git does 3-way merge using common ancestor § Instead of just moving branch pointer forward, Git creates a new snapshot and a new commit that points to it called a “merge commit” $ git checkout master $ git merge feature C2 C3 C4 C5 feature C0 C1 Common Ancestor Branch Tip Branch Tip master
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  12 © 2018 BrentLaster@BrentCLaster 12 @BrentCLaster Merging: What is a Rebase? § Rebase – take all of the changes that were committed on one branch and replay them on another one. § Concepts in simple syntax (git rebase branch2 [branch1]): § Move branchpoint of branch (carrying along all commits) to be off of a different commit (new base) § Current branch (or branch1 if supplied) is one having its branchpoint moved § Branch2 (or commit) provided as first/only argument is the new branchpoint § In simple case, think of it as “pick up branch1 entirely and move its branchpoint to be after the tip of branch2)” § Process: § Goes to the common ancestor of the two branches (the one you are on and the one you are rebasing onto) § Gets the diff introduced by each commit of the branch you are on, saving them to temporary files § Applies each change in turn § Moves the branch to the new rebase point $ git checkout feature $ git rebase master C3 C4 C5 C0 Common Ancestor C2 feature C1 C3’ C5’ C2 master
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  13 © 2018 BrentLaster@BrentCLaster 13 @BrentCLaster Command: Git Stash § Purpose -- allow you to keep a backup copy of your work that hasn’t been committed yet § Use case - you want to switch branches but don’t want to lose work that hasn’t been committed; you want to save something you’ve tried and may want to come back to § Syntax:
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  14 © 2018 BrentLaster@BrentCLaster 14 @BrentCLaster Stash Staging Area Staging Area Local Repository Working Directory stash@{0} Staging Area * Working Directory * stash@{1} Staging Area ** Working Directory **# stash@{0} Staging Area *** stash@{2} ****** ****** stash@{1} stash@{0} stash@{0}stash@{1} stash@{1}stash@{2} “cool feature” Working Directory *** > git stash> git stash -u # > git stash save “cool feature”> git stash apply stash@{1}$ git stash pop stash@{2}
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  15 © 2018 BrentLaster@BrentCLaster 15 @BrentCLaster Command: Git Reset § Purpose -- allow you to “roll back” so that your branch points at a previous commit ; optionally also update staging area and working directory to that commit § Use case - you want to update your local environment back to a previous point in time; you want to overwrite or a local change you’ve made § Syntax: § Warning: --hard overwrites everything
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  16 © 2018 BrentLaster@BrentCLaster 16 @BrentCLaster Command: Git Revert § Purpose -- allow you to “undo” by adding a new change that cancels out effects of previous one § Use case - you want to cancel out a previous change but not roll things back § Syntax: § Note: The net result of using this command vs. reset can be the same. If so, and content that is being reset/revert has been pushed such that others may be consuming it, preference is for revert.
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  17 © 2018 BrentLaster@BrentCLaster 17 @BrentCLaster Local Repository Reset and Revert git reset --hard 87ba8bc git reset current~1 [--mixed] git revert HEAD Line 1 Staging Area Working Directory XYZ ABC Line 1 87ba8bc 43bd3ef d21be2c Line 1 Line 2 Line 3 c1c8bd4 Line 1 Line 2 Line 1 Line 2 Line 1Line 1 Line 1 Line 2 tag: current Line 1 Line 2
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  18 © 2018 BrentLaster@BrentCLaster 18 @BrentCLaster Command: Git Rerere (Reuse Recorded Resolution) § Purpose -- allows recording of how you solve a merge situation and then can automatically resolve the same situation in the same way if needed later § Use case - trial and repeated merges; merging newer versions of a branch with the same conflicts into a newer one periodically; resolve conflicts after reset or revert; applicable to any repeated merge case: rebase, merge § Syntax: § Note: This is a “state” command. Enabled by turning on a state in Git, rather than just running a command § Enabled via git config --global rerere.enabled 1 » Then runs automatically § Invoked directly via git rerere for related commands or options
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  19 © 2018 BrentLaster@BrentCLaster 19Local Repository feature Staging Area File B Working Directory File C File A File B master File A File C File B File A File C File BFile B File B <<>> File BFile A File CFile BFile A File C rr-cache File A File C File B <<>> preimage postimage File B Git Rerere 1
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  20 © 2018 BrentLaster@BrentCLaster 20Local Repository feature Staging Area File B Working Directory File C File A File B master File A File C File B File A File C File BFile B File B <<>> File BFile A File CFile BFile A File C rr-cache File A File C File B <<>> preimage postimage File B Git Rerere 2
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  21 © 2018 BrentLaster@BrentCLaster 21 @BrentCLaster Command: Bisect § Purpose - Use “automated” binary search through Git’s history to find a specific commit that first introduced a problem (i.e. “first bad commit”) § Use case - Quickly locate the commit in Git’s history that introduced a bug § Syntax:
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  22 © 2018 BrentLaster@BrentCLaster 22 @BrentCLaster Git Bisect § Use “automated” binary search to find change that first introduced a bug (i.e. “first bad commit”) § Initiate with git bisect start § Can pass range to start option to identify bad and good revisions – i.e. git bisect start HEAD HEAD~10 § Identify first “bad” commit, usually current one via git bisect bad § Identify a “good” (functioning) commit via git bisect good § From there, git will do a binary search and pick a “middle” commit to checkout. § Try the checked out version and indicate git bisect good or git bisect bad depending on whether it works or not. § Process repeats until git can identify “first bad” commit/revision. § Can grab previous good revision by specifying “first bad”^ § Can update, create new branch, rebase, etc. to isolate good revisions. § Other useful options to git bisect: log, visualize, reset, skip, run
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  23 © 2018 BrentLaster@BrentCLaster 23 @BrentCLaster LOCAL REPOSITORY Version 1Version 1 Bisect § checkout latest version § try code § git bisect start § git bisect bad § checkout earlier version ( user checks out) § try code § git bisect good (bisect checks out version 5) § try code § git bisect good (bisect checks out version 7) § try code § git bisect bad (bisect checks out version 6) § try code § git bisect bad (git reports version 6 as the first bad commit) Version 3 Version 4 Version 5 Version 6 Version 7 Version 8 Version 9 Version 10Version 10 Version 5 Version 2 Version 7 Version 6 FIRST BAD COMMIT WORKING DIRECTORY
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  24 © 2018 BrentLaster@BrentCLaster 24 @BrentCLaster Background: Switching between Branches Command: git checkout <branch> git checkout master § Does three things § Moves HEAD pointer back to <branch> § Reverts files in working directory to snapshot pointed to by <branch> § Updates indicators git checkout testing git checkout master git checkout testing § git branch Local Repository Working Directory * * 87ba8bc 43bd3ef d21be2c c1c8bd4 master testing
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  25 © 2018 BrentLaster@BrentCLaster 25 @BrentCLaster Worktrees - syntax and usage § Syntax § git worktree add [-f] [--detach] [-b <new-branch>] <path> [<branch>] § git worktree list [--porcelain] § git worktree prune [-n] [-v] [--expire <expire>] § Subcommands § Add - create a separate working tree for specified branch » has checked out copy of the branch » if no branch specified, uses same name as temp area § List - lists out current set of working trees active for this repo » porcelain - consistent and backwards-compatible format § Prune - removes worktree information from the .git area » only applies after worktree directory tree has been removed
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  26 © 2018 BrentLaster@BrentCLaster 26 @BrentCLaster Command: Worktree § Purpose - Allows multiple, separate Working Areas attached to one Local Repository § Use case - Simultaneous development in multiple branches § Syntax § Notes § “Traditional” working directory is called the main working tree; Any new trees you create with this command are called linked working trees § Information about working trees is stored in the .git area (assuming .git default GIT_DIR is used) § Working tree information is stored in .git/worktrees/<name of worktree>.
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  27 © 2018 BrentLaster@BrentCLaster 27 @BrentCLaster Worktree § git worktree add -b exp tree1 § git worktree add -b prod tree2 Remote Repository Main Working Tree Server Add Commit Push Pull Staging Area Local Repository Working Directory (master) Local Machine worktrees/ tree1 gitdir HEAD etc. tree1 Linked Working Tree Staging Area Working Directory (exp) gitdir HEAD etc. tree2 Linked Working Tree Staging Area Working Directory (prod) tree2
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  28 © 2018 BrentLaster@BrentCLaster 28 @BrentCLaster Command: Subtree § Purpose - Allows including a copy of a separate repository with your current repository § Use case - include a copy of a Git repository for one or more dependencies along with the original repository for a project § Syntax § Notes § No links like a submodule - just a copy in a subdirectory § Advantage - no links to maintain § Disadvantage - extra content to carry around with your project git subtree add -P <prefix> <commit> git subtree add -P <prefix> <repository> <ref> git subtree pull -P <prefix> <repository> <ref> git subtree push -P <prefix> <repository> <ref> git subtree merge -P <prefix> <commit> git subtree split -P <prefix> [OPTIONS] [<commit>]
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  29 © 2018 BrentLaster@BrentCLaster 29 @BrentCLaster Subtrees - overall view
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  30 © 2018 BrentLaster@BrentCLaster 30 @BrentCLaster Subtrees - adding a project as a subtree § Simplest form, specify: prefix, remote path to repository, branch (optional) § Suppose we clone down a project - myproject § And, on the remote side, we have another project, subproj. § Now, we can add subproj as a subtree of myproject (--prefix subproject). § Subtree now shows subproject in structure and history
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  31 © 2018 BrentLaster@BrentCLaster 31 @BrentCLaster Command: (Interactive) Rebase § Purpose - allows you to run operations against commits in the git history § Use case - you need to make some kind of modification to one or more commits in the repository (rewrite history) § Syntax § Notes - creates an interactive script/batch file to modify commits § Cautions - don’t use this on anything already pushed
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  32 © 2018 BrentLaster@BrentCLaster 32 @BrentCLaster Interactive Rebase § Choose set of commits § Initiate interactive rebase § Git presents initial script § Modify commands (save and exit) § Act on prompts § Commits are updated
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  33 © 2018 BrentLaster@BrentCLaster 33 @BrentCLaster Command: Notes § Purpose - Add additional information to objects in the Git repository or look at such information § Use case - At some point after making a commit, you may decide that there are additional comments or other non-code information that you’d like to add with the commit - without changing the commit itself. § Syntax git notes [list [<object>]] git notes add [-f] [--allow-empty] [-F <file> | -m <msg> | (-c | -C) <object>] [<object>] git notes copy [-f] ( --stdin | <from-object> <to-object> ) git notes append [--allow-empty] [-F <file> | -m <msg> | (-c | -C) <object>] [<object>] git notes edit [--allow-empty] [<object>] git notes show [<object>] git notes merge [-v | -q] [-s <strategy> ] <notes-ref> git notes merge --commit [-v | -q] git notes merge --abort [-v | -q] git notes remove [--ignore-missing] [--stdin] [<object>…] git notes prune [-n | -v] git notes get-ref
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  34 © 2018 BrentLaster@BrentCLaster 34 @BrentCLaster Notes § Create a note § Create a note in a custom namespace (add --ref) § View a note (for a specific revision) § List notes in log
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  35 © 2018 BrentLaster@BrentCLaster 35 @BrentCLaster Command: grep § Purpose - provides a convenient (and probably familiar) way to search for regular expressions in your local Git environment. § Use case - self-explanatory § Syntax git grep [-a | --text] [-I] [--textconv] [-i | --ignore-case] [-w | --word-regexp] [-v | --invert-match] [-h|-H] [--full-name] [-E | --extended-regexp] [-G | --basic-regexp] [-P | --perl-regexp] [-F | --fixed-strings] [-n | --line-number] [-l | --files-with-matches] [-L | --files-without-match] [(-O | --open-files-in-pager) [<pager>]] [-z | --null] [-c | --count] [--all-match] [-q | --quiet] [--max-depth <depth>] [--color[=<when>] | --no-color] [--break] [--heading] [-p | --show-function] [-A <post-context>] [-B <pre-context>] [-C <context>] [-W | --function-context] [--threads <num>] [-f <file>] [-e] <pattern> [--and|--or|--not|(|)|-e <pattern>…] [ [--[no-]exclude-standard] [--cached | --no-index | --untracked] | <tree>…] [--] [<pathspec>…] § Notes § Several options are similar to OS grep options
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  36 © 2018 BrentLaster@BrentCLaster 36 @BrentCLaster grep § Default behavior - search for all instances of an expression across all tracked files in working directory § Search for all instances off expression “database” across all java files (note use of -- ) § -p option tells Git to try and show header of method or function where search target was found § --break - make output easier to read § --heading - prints filename above output § boolean operators § search in staging area § search in specific commit(s)
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  37 © 2018 BrentLaster@BrentCLaster 37 That’s all - thanks!