Introduction
Fossil shares many similarities with Git. In many cases, the
sub-commands are identical: fossil bisect
does essentially the
same thing as git bisect
, for example.
This document covers the cases where there is no simple 1:1 mapping, usually because of intentional design differences in Fossil that prevent it from working exactly like Git. We choose to explain these differences rather than provide a simple “translation dictionary,” since to understand the conversion, you need to know why the difference exists.
We focus on practical command examples here, leaving discussions of the philosophical underpinnings that drive these command differences to another document. The case studies do get a bit philosophical, but it is with the aim of illustrating how these Fossil design differences cause Fossil to behave materially differently from Git in everyday operation.
We present this from the perspective of Git users moving to Fossil, but it is also possible to read this document as a Fossil user who speaks only pidgin Git, who may often have questions of the form, “Now how do I do X in Git again?”
This document’s authors are intimately familiar with Fossil, so it is difficult for us to anticipate the perspective of people who are intimately familiar with Git. If you have a lot of prior Git experience, we welcome your contributions and questions on the Fossil Forum.
While we do try to explain Fossil-specific terminology inline here as-needed, you may find it helpful to skim the Fossil glossary. It will give you another take on our definitions here, and it may help you to understand some of the other Fossil docs better.
Repositories And Checkouts Are Distinct
A repository and a check-out are distinct concepts in Fossil, whereas the two are collocated by default with Git. This difference shows up in several separate places when it comes to moving from Git to Fossil.
Checkout Workflows
A Fossil repository is a SQLite database storing the entire history of a
project. It is not normally stored inside the working tree.
A Fossil working tree — also called a check-out — is a directory
that contains a snapshot of your project that you are currently working
on, extracted for you from the repository database file by the fossil
program.
Git commingles these two by default, with the repository stored in a
.git
subdirectory underneath your working directory. There are ways to
emulate the Fossil working style in Git, but because they’re not
designed into the core concept of the tool, Git tutorials usually
advocate a switch-in-place working mode instead, so that is how most
users end up working with Git. Contrast Fossil’s check-out workflow
document to see the practical differences.
There is one Git-specific detail we wish to add beyond what that document already covers. This command:
git checkout some-branch
…is best given as:
fossil update some-branch
…in Fossil. There is a fossil checkout
command, but it has
several differences that make it less broadly useful
than fossil update
in everyday operation, so we recommend that
Git users moving to Fossil develop a habit of typing fossil up
rather
than fossil checkout
. That said, one of those differences does match
up with Git users’ expectations: fossil checkout
doesn’t pull changes
from the remote repository into the local clone as fossil update
does.
We think this is less broadly useful, but that’s the subject of the next
section.
Update vs Pull
The closest equivalent to git pull
is not
fossil pull
, but in fact fossil up
.
This is because
Fossil tends to follow the CVS command design: cvs up
pulls
changes from the central CVS repository and merges them into the local
working directory, so that’s what fossil up
does, too. (This design
choice also tends to make Fossil feel comfortable to Subversion
expatriates.)
The fossil pull
command is simply the reverse of
fossil push
, so that fossil sync
is functionally equivalent
to:
fossil push ; fossil pull
There is no implicit “and update the local working directory” step in Fossil’s
push, pull, or sync commands, as there is with git pull
.
Someone coming from the Git perspective may perceive that fossil up
has two purposes:
Without the optional
VERSION
argument, it updates the working checkout to the tip of the current branch, asgit pull
does.Given a
VERSION
argument, it updates to the named version. If that’s the name of a branch, it updates to the tip of that branch, asgit checkout BRANCH
does.
In fact, these are the same operation, so they’re the same command in
Fossil. The first form simply allows the VERSION
to be implicit: the
tip of the current branch.
We think this is a more sensible command design than git pull
vs
git checkout
. (…vs git checkout
vs git checkout
!)
Closing a Check-Out
The fossil close
command dissociates a check-out directory from the
Fossil repository database, nondestructively inverting fossil open
.
(Contrast its closest inverse, git worktree remove
, which is
destructive in Git!) This Fossil command does not
remove the managed files, and unless you give the --force
option, it won’t let you close the check-out with uncommitted changes to
those managed files.
The close
command also refuses to run without --force
when you have
certain other precious per-checkout data that Fossil stores in the
.fslckout
file at the root of a check-out directory. This is a SQLite
database that keeps track of local state such as what version you have
checked out, the contents of the stash for that working directory, the
undo buffers, per-checkout settings, and so forth. The stash
and undo buffers are considered precious uncommitted changes,
so you have to force Fossil to discard these as part of closing the
check-out.
Thus, .fslckout
is not the same thing as .git
!
In native Windows builds of Fossil — that is, excluding Cygwin and WSL
builds, which follow POSIX conventions — this file is called _FOSSIL_
instead to get around the historical 3-character extension limit with
certain legacy filesystems.
Closing a check-out directory is a rare operation. One use case
is that you’re about to delete the directory, so you want Fossil to forget about it
for the purposes of commands like fossil all
. Even that isn’t
necessary, because Fossil will detect that this has happened and forget
the working directory for you.
Git Worktrees
There are at least three different ways to get Fossil-style multiple check-out directories with Git.
The old way is to simply symlink the .git
directory between working
trees:
mkdir ../foo-branch
ln -s ../actual-clone-dir/.git .
git checkout foo-branch
The symlink trick has a number of problems, the largest being that
symlinks weren’t available on Windows until Vista, and until the Windows
10 Creators Update was released in spring of 2017, you had to be an
Administrator to use the feature besides. (Source) Git solved
this problem back when Windows XP was Microsoft’s current offering
with the git-worktree
command, added in Git 2.5:
git worktree add ../foo-branch foo-branch
cd ../foo-branch
That is approximately equivalent to this in Fossil:
mkdir ../foo-branch
cd ../foo-branch
fossil open /path/to/repo.fossil foo-branch
The Fossil alternative is wordier, but this tends to be one-time setup, not something you do everyday. This author keeps a “scratch” checkout for cases where is isn’t appropriate to reuse the “trunk” checkout. The other peer checkouts therefore tend to track long-lived branches, so they rarely change once a development machine is set up.
That then leads us to the closest equivalent in Git to closing a Fossil check-out:
git worktree remove .
Note, however, that unlike fossil close
, once the Git command
determines that there are no uncommitted changes, it blows away all of
the checked-out files! Fossil’s alternative is shorter, easier to
remember, and safer.
There’s another way to get Fossil-like separate worktrees in Git:
git clone --separate-git-dir repo.git https://example.com/repo
This allows you to have your Git repository directory entirely separate
from your working tree, with .git
in the check-out directory being a
file that points to ../repo.git
, in this example.
As of Fossil 2.14, there is a direct equivalent:
fossil clone https://example.com/repo
It’s a shorter command because we deduce repo.fossil
and the repo/
working directory from the last element of the path in the URI. If you
wanted to override both deductions, you’d say:
fossil clone --workdir foo https://example.com/repo/bar
That gets you bar.fossil
with a foo/
working directory alongside it.
Init In Place
To illustrate the differences that Fossil’s separation of repository from working directory creates in practice, consider this common Git “init in place” method for creating a new repository from an existing tree of files, perhaps because you are placing that project under version control for the first time:
cd long-established-project
git init
git add *
git commit -m "Initial commit of project."
The closest equivalent in Fossil is:
cd long-established-project
fossil init .fsl
fossil open --force .fsl
fossil add *
fossil ci -m "Initial commit of project."
Note that unlike in Git, you can abbreviate the “commit
” command in
Fossil as “ci
” for compatibility with CVS, Subversion, etc.
This creates a .fsl
repo DB at the root of the project check-out to
emulate the .git
repo dir. We have to use the --force
flag on
opening the new repo because Fossil expects you to open a repo into an
empty directory in order to avoid spamming the contents of a repo over
an existing directory full of files. Here, we know the directory
contains files that will soon belong in the repository, though, so we
override this check. From then on, Fossil works like Git, for the
purposes of this example.
We’ve drawn this example to create a tight parallel between Fossil and
Git, not to commend this .fsl
-at-project-root trick to you. A better
choice would be ~/museum/home/long-established-project.fossil
, if
you’re following the directory scheme exemplified above. That said, it
does emphasize an earlier point: Fossil doesn’t care where you put the
repo DB file or what you name it.
Fossil’s Timeline Is The “Log”
Git users often need to use the git log
command to dig linearly through
commit histories due to its weak data model, giving O(n)
performance.
Fossil parses a huge amount of information out of commits that allow it
to produce its timeline CLI and its /timeline
web view
using indexed SQL lookups, which generally have the info you would have
to manually extract from git log
, produced much more quickly than Git
can, all else being equal: operations over SQLite’s B-tree data structures
generally run in O(log n) time, faster than O(n) for equal n when the
constants are equal. Yet the constants are not equal because Fossil
reads from a single disk file rather than visit potentially many
files in sequence as Git must, so the OS’s buffer cache can result in
still better performance.
Unlike Git’s log, Fossil’s timeline shows info across branches by
default, a feature for maintaining better situational awareness. Although the
fossil timeline
command has no way to show a single branch’s commits,
you can restrict your view like this using the web UI equivalent by
clicking the name of a branch on the /timeline
or /brlist
page. (Or
manually, by adding the r=
query parameter.) Note that even in this
case, the Fossil timeline still shows other branches where they interact
with the one you’ve referenced in this way; again, better situational
awareness.
Emulating git log
If you truly need a backwards-in-time-only view of history in Fossil to
emulate git log
, this is as close as you can currently come:
fossil timeline parents current
Again, though, this isn’t restricted to a single branch, as git log
is.
Another useful rough equivalent is:
git log --raw
fossil time -v
This shows what changed in each version, though Fossil’s view is more a
summary than a list of raw changes. To dig deeper into single commits,
you can use Fossil’s info
command or its /info
view.
Inversely, you may more exactly emulate the default fossil timeline
output with git log --name-status
.
What Changed?
A related — though deprecated — command is git whatchanged
, which gives results similar to
git log --raw
, so we cover it here.
Though there is no fossil whatchanged
command, the same sort of
information is available. For example, to pull the current changes from
the remote repository and then inspect them before updating the local
working directory, you might say this in Git:
git fetch
git whatchanged ..@{u}
…which you can approximate in Fossil as:
fossil pull
fossil up -n
fossil diff --from tip
To invert the diff
to show a more natural patch, the command needs to
be a bit more complicated, since you can’t currently give --to
without --from
.
fossil diff --from current --to tip
Rather than use the “dry run” form of the update
command, you can
say:
fossil timeline after current
…or if you want to restrict the output to the current branch:
fossil timeline descendants current
Symbolic Check-In Names
Note the use of human-readable symbolic version names in Fossil rather than Git’s cryptic notations.
For a more dramatic example of this, let us ask Git, “What changed since the beginning of last month?” being October 2020 as I write this:
git log master@{2020-10-01}..HEAD
That’s rather obscure! Fossil answers the same question with a simpler command:
fossil timeline after 2020-10-01
You may need to add -n 0
to bypass the default output limit of
fossil timeline
, 20 entries. Without that, this command reads
almost like English.
Some Git users like to write commands like the above so:
git log @{2020-10-01}..@
Is that better? “@” now means two different things: an at-time reference
and a shortcut for HEAD
!
If you are one of those that like short commands, Fossil’s method is
less cryptic: it lets you shorten words in most cases up to the point
that they become ambiguous. For example, you may abbreviate the last
fossil
command in the prior section:
fossil tim d c
…beyond which the timeline
command becomes ambiguous with ticket
.
Some Fossil users employ shell aliases, symlinks, or scripts to shorten the command still further:
alias f=fossil
f tim d c
Granted, that’s rather obscure, but you you can also choose something
intermediate like “f time desc curr
”, which is reasonably clear.
Detached HEAD State
The SQL indexes in Fossil which we brought up above have a very useful side benefit: you cannot have a detached HEAD state in Fossil, the source of untold pain and data loss in Git. It simply cannot be done in Fossil, because the indexes always let us find our way back into the hash tree.
Summary Line Convention In Commit Comments
The Git convention of a length-limited summary line at the start
of commit comments is not enforced or obeyed by default in Fossil.
However, there is a setting under Admin → Timeline → “Truncate comment
at first blank line (Git-style)” to change this for /timeline
displays. Alternately, you could enable the “Allow block-markup in
timeline” setting under Admin → Timeline, then apply local skin
customizations to put that first comment in in bold or whatever
suits.
Because this isn’t a typical Fossil convention, you’re likely to find
other odd differences between it and Git-based infrastructure. For
instance, Vim doesn’t ship with syntax support for Fossil commit
messages if you set EDITOR=vim
in your shell environment, so you won’t
get over-limit highlighting for first-line text beyond the 50th
character and such, because it doesn’t recognize Fossil commit messages
and apply similar rules as to Git commit messages.
There Is No Staging Area
Fossil omits the "Git index" or "staging area" concept. When you
type "fossil commit
" all changes in your check-out are committed,
automatically. There is no need for the "-a" option as with Git.
If you only want to commit some of the changes, list the names of the files or directories you want to commit as arguments, like this:
fossil commit src/feature.c doc/feature.md examples/feature
Note that the last element is a directory name, meaning “any changed
file under the examples/feature
directory.”
Although there are currently no
commit splitting features in Fossil like
git add -p
, git commit -p
, or git rebase -i
, you can get the same
effect by converting an uncommitted change set to a patch and then
running it through Patchouli.
Rather than use fossil diff -i
to produce such a patch, a safer and
more idiomatic method would be:
fossil stash save -m 'my big ball-o-hackage'
fossil stash diff > my-changes.patch
That stores your changes in the stash, then lets you operate on a copy of that patch. Each time you re-run the second command, it will take the current state of the working directory into account to produce a potentially different patch, likely smaller because it leaves out patch hunks already applied.
In this way, the combination of working tree and stash replaces the need for Git’s index feature.
This also solves a philosophical problem with git commit -p
: how can
you test that a split commit doesn’t break anything if you do it as part
of the commit action? Git’s lack of an autosync feature means you can
commit locally and then rewrite history if the commit doesn’t work out,
but we’d rather make changes only to the working directory, test the
changes there, and only commit once we’re sure it’s right.
This also explains why we don’t have anything like git rebase -i
to split an existing commit: in Fossil, commits are commitments, not
something you want to go back and rewrite later.
If someone does contribute a commit splitting feature to Fossil,
we’d expect it to be an interactive form of
fossil stash apply
, rather than follow Git’s ill-considered
design leads.
Create Branches at Point of Need, Rather Than Ahead of Need
Fossil prefers that you create new branches as part of the first commit on that branch:
fossil commit --branch my-branch
If that commit is successful, your local check-out directory is then
switched to the tip of that branch, so subsequent commits don’t need the
“--branch
” option. You simply say fossil commit
again to continue
adding commits to the tip of that branch.
To switch back to the parent branch, say something like:
fossil update trunk
(This is approximately equivalent to git checkout master
.)
Fossil does also support the Git style, creating the branch ahead of need:
fossil branch new my-branch
fossil up my-branch
...work on first commit...
fossil commit
This is more verbose, giving the same overall effect though the initial actions are inverted: create a new branch for the first commit, switch the check-out directory to that branch, and make that first commit. As above, subsequent commits are descendants of that initial branch commit. We think you’ll agree that creating a branch as part of the initial commit is simpler.
Fossil also allows you to move a check-in to a different branch
after you commit it, using the "fossil amend
" command.
For example:
fossil amend current --branch my-branch
This works by inserting a tag into the repository that causes the web UI to relabel commits from that point forward with the new name. Like Git, Fossil’s fundamental data structure is the interlinked DAG of commit hashes; branch names are supplemental data for making it easier for the humans to understand this DAG, so this command does not change the core history of the project, only annotate it for better display to the humans.
(The version string “current” is one of the special check-in names in Fossil. See
that document for the many other names you can give to “amend
”, or
indeed to any other Fossil command documented to accept a VERSION
or
NAME
string.)
Autosync
Fossil’s autosync feature, normally enabled, has no equivalent in Git. If you want Fossil to behave like Git, you can turn it off:
fossil set autosync 0
However, it’s better to understand what the feature does and why it is enabled by default.
When autosync is enabled, Fossil automatically pushes your changes
to the remote server whenever you "fossil commit
", and it
pulls all remote changes down to your local clone of the repository as
part of a "fossil update
".
This provides most of the advantages of a centralized version control
system while retaining the advantages of distributed version control:
Your work stays synced up with your coworkers’ efforts as long as your machine can connect to the remote repository. At need, you can go off-network and continue work atop the last version you synced with the remote.
It provides immediate off-machine backup of your commits. Unlike centralized version control, though, you can still work while disconnected; your changes will sync up with the remote once you get back online.
Because there is little distinction between the clones in the Fossil model — unlike in Git, where clones often quickly diverge from each other, quite possibly on purpose — the backup advantage applies in inverse as well: if the remote server falls over dead, one of those with a clone of that repository can stand it back up, and everyone can get back to work simply by re-pointing their local repo at the new remote. If the failed remote comes back later, it can sync with the new central version, then perhaps take over as the primary source of truth once again.
(There are caveats to this, covered elsewhere.)
Sync Is All-or-Nothing
Fossil does not support the concept of syncing, pushing, or pulling individual branches. When you sync/push/pull in Fossil, it processes all artifacts in its hash tree: branches, tags, wiki articles, tickets, forum posts, technotes… This is not quite “everything,” full stop, but it’s close.
Furthermore, branch names sync automatically in Fossil, not just the content of those branches. That means this common Git command:
git push origin master
…is simply this in Fossil:
fossil push
Fossil doesn’t need to be told what to push or where to push it: it just keeps using the same remote server URL you gave it last until you tell it to do something different, and it pushes all branches, not just one named local branch.
The Main Branch Is Called "trunk
"
In Fossil, the default name for the main branch
is "trunk
". The "trunk
" branch in Fossil corresponds to the
"master
" branch in stock Git or to the “main
” branch in GitHub.
Because the fossil git export
command has to work with both stock Git
and with GitHub, Fossil uses Git’s traditional default rather than
GitHub’s new default: your Fossil repo’s “trunk” branch becomes “master”
when mirroring to GitHub unless you give the --mainbranch
option added in Fossil 2.14.
We do not know what happens on subsequent exports if you later rename this branch on the GitHub side.
The "fossil status
" Command Does Not Show Unmanaged Files
The "fossil status
" command shows you what files in your check-out have
been edited and scheduled for adding or removing at the next commit.
But unlike "git status
", the "fossil status
" command does not warn
you about unmanaged files in your local check-out. There is a separate
"fossil extras
" command for that.
There Is No Rebase
Fossil does not support rebase, on purpose.
This is a deliberate design decision that the Fossil community has thought about carefully and discussed many times, resulting in the linked document. If you are fond of rebase, you should read it carefully before expressing your views: it not only answers many of the common arguments in favor of rebase known at the time the document’s first draft was written, it’s been revised multiple times to address less common objections as well. Chances are not good that you are going to come up with a new objection that we haven’t already considered and addressed there.
There is only one sub-feature of git rebase
that is philosophically
compatible with Fossil yet which currently has no functional equivalent.
We covered this and the workaround for its lack above.
Colorized Diffs
The graphical diffs in the Fossil web UI and fossil diff --tk
use
color to distinguish insertions, deletions, and replacements, but unlike
with git diff
when the output is to an ANSI X3.64 capable terminal,
fossil diff
does not.
There are a few easy ways to add this feature to Fossil, though.
One is to install
colordiff
, which is included in many package systems,
then say:
fossil set --global diff-command 'colordiff -wu'
Because this is unconditional, unlike git diff --color=auto
, you will
then have to remember to add the -i
option to fossil diff
commands
when you want color disabled, such as when producing patch(1)
files
or piping diff output to another
command that doesn’t understand ANSI escape sequences. There’s an
example of this below.
Another way, which avoids this problem, is to say instead:
fossil set --global diff-command 'git diff --no-index'
This delegates fossil diff
to git diff
by using the latter’s
ability to run on files not inside any repository.
Showing Information About Commits
While there is no direct equivalent to Git’s “show
” command, similar
functionality is present in Fossil under other commands:
Show a Patch for a Commit
git show -p COMMIT_ID
…gives much the same output as
fossil diff --checkin COMMIT_ID
…only without the patch email header. Git comes out of the LKML world, where emailing a patch is a normal thing to do. Fossil is designed for cohesive teams where such drive-by patches are rarer.
You can use any of Fossil’s special check-in names in place of
the COMMIT_ID
in this and later examples. Fossil docs usually say
“VERSION
” or “NAME
” where this is allowed, since the version string
or name might not refer to a commit ID, but instead to a forum post, a
wiki document, etc. For instance, the following command answers the question “What did
I just commit?”
fossil diff --checkin tip
…or equivalently using a different symbolic commit name:
fossil diff --from prev
Show a Specific Commit Message
git show -s COMMIT_ID
…is
fossil time -n 1 COMMIT_ID
…or with a shorter, more obvious command, though with more verbose output:
fossil info COMMIT_ID
The fossil info
command isn’t otherwise a good equivalent to
git show
; it just overlaps its functionality in some areas. Much of
what’s missing is present in the corresponding /info
web
view, though.
Diff Statistics
Fossil’s closest internal equivalent to commands like
git show --stat
is:
fossil diff -i --from 2020-04-01 --numstat
The --numstat
output is a bit cryptic, so we recommend delegating
this task to the widely-available diffstat
tool, which gives
a histogram in its default output mode rather than bare integers:
fossil diff -i -v --from 2020-04-01 | diffstat
We gave the -i
flag in both cases to force Fossil to use its internal
diff implementation, bypassing your local diff-command
setting.
The --numstat
option has no effect when you have an external diff
command set, and some diff command alternatives like
colordiff
(covered above) produce output that confuses diffstat
.
If you leave off the -v
flag in the second example, the diffstat
output won’t include info about any newly-added files.
Branch And Tag Names
Fossil has no special restrictions on the names of tags and branches, though you might want to keep Git's tag and branch name restrictions in mind if you plan on mirroring your Fossil repository to GitHub.
Fossil does not require tag and branch names to be unique. It is
common, for example, to put a "release
" tag on every release for a
Fossil-hosted project. This does not create a conflict in Fossil, since
Fossil resolves the ambiguity in a predictable way: the newest match
wins. Therefore, “fossil up release
” always gets you the current
release in a project that uses this tagging convention.
The fossil git export
command squashes repeated tags down to a
single instance to avoid confusing Git, exporting only the newest tag,
emulating Fossil’s own ambiguity resolution rule as best it can within
Git’s limitations.
Cherry-Picking And Reverting Commits
Git’s separate "git cherry-pick
" and “git revert
” commands are
options to the fossil merge
command: --cherrypick
and
--backout
, respectively.
Unlike in Git, the Fossil file format remembers cherrypicks and backouts and can later show them as dashed lines on the graphical timeline.
File Moves And Renames Are Soft By Default
The "fossil mv
" and "fossil rm
" commands work like they
do in CVS in that they schedule the changes for the next commit by
default: they do not actually rename or delete the files in your
check-out.
If you don’t like that default, you can change it globally:
fossil setting --global mv-rm-files 1
Now these commands behave like in Git in any Fossil repository where this setting hasn’t been overridden locally.
If you want to keep Fossil’s soft mv/rm
behavior most of the time, you
can cast it away on a per-command basis:
fossil mv --hard old-name new-name
Case Study 1: Checking Out a Version by Date
Let’s get into something a bit more complicated: a case study showing how the concepts lined out above cause Fossil to materially differ in day-to-day operation from Git.
Why would you want to check out a version of a project by date? Perhaps
your customer gave you a vague bug report referencing only a
date rather than a version. Or, you may be poking semi-randomly through
history to find a “good” version to anchor the start point of a
fossil bisect
operation.
My search engine’s first result for “git checkout by date” is this
highly-upvoted accepted Stack Overflow answer. The first command
it gives is based on Git’s rev-parse
feature:
git checkout master@{2020-03-17}
There are a number of weaknesses in this command. From least to most critical:
It’s a bit cryptic. Leave off the refname or punctuation, and it means something else. You cannot simplify the cryptic incantation in the typical use case.
A date string in Git without a time will be interpreted as “at the local wall clock time on the given date,” so the command means something different from one second to the next! This can be a serious problem if there are multiple commits on that date, because the command will give different results depending on the time of day you run it.
It gives misleading output if there is no close match for the date in the local reflog. It starts out empty after a fresh clone, and while it does build up as you use that clone, Git automatically prunes the reflog to 90 days of history by default. This means the command above can give different results from one machine to the next, or even from one day to the next on the same clone.
The command won’t fail outright if the reflog can’t resolve the given date: it simply gives the closest commit it can come up with, even if it’s months or years out from your target! Sometimes it gives a warning about the reflog not going back far enough to give a useful result, and sometimes it doesn’t. If you’re on a fresh clone, you are likely to get the “tip” commit’s revision ID no matter what date value you give.
Git tries its best, but because it’s working from a purgeable and possibly-stale local cache, you cannot trust its results.
Consequently, we cannot recommend this command at all. It’s unreliable even in the best case.
That same Stack Overflow answer therefore goes on to recommend an entirely different command:
git checkout $(git rev-list -n 1 --first-parent --before="2020-03-17" master)
We believe you get such answers to Git help requests in part because of its lack of an always-up-to-date index into its log and in part because of its “small tools loosely joined” design philosophy. This sort of command is therefore composed piece by piece:
“Oh, I know, I’ll search the rev-list, which outputs commit IDs by
parsing the log backwards from HEAD
! Easy!”
git rev-list --before=2020-03-17
“Blast! Forgot the commit ID!”
git rev-list --before=2020-03-17 master
“Double blast! It just spammed my terminal with revision IDs! I need to limit it to the single closest match:
git rev-list -n 1 --before=2020-03-17 master
“Okay, it gives me a single revision ID now, but is it what I’m after? Let’s take a look…”
git show $(git rev-list -n 1 --before=2020-03-17 master)
“Oops, that’s giving me a merge commit, not what I want.
Off to search the web… Okay, it says I need to give either the
--first-parent
or --no-merges
flag to show only regular commits,
not merge-commits. Let’s try the first one:”
git show $(git rev-list -n 1 --first-parent --before=2020-03-17 master)
“Better. Let’s check it out:”
git checkout $(git rev-list -n 1 --first-parent --before=2020-03-17 master)
“Success, I guess?”
This vignette is meant to explain some of Git’s popularity: it rewards the sort of people who enjoy puzzles, many of whom are software developers and thus need a tool like Git. Too bad if you’re just a normal user.
And too bad if you’re a Windows user who doesn’t want to use Git Bash, since neither of the stock OS command shells have a command interpolation feature needed to run that horrid command.
This alternative command still has weakness #2 above: if you run the
second git show
command above on Git’s own repository, your
results may vary because there were four non-merge commits to Git on the
17th of March, 2020.
You may be asking with an exasperated huff, “What is your point, man?” The point is that the equivalent in Fossil is simply:
fossil up 2020-03-17
…which will always give the commit closest to midnight UTC on the 17th of March, 2020, no matter whether you do it on a fresh clone or a stale one. The answer won’t shift about from one clone to the next or from one local time of day to the next. We owe this reliability and stability to three Fossil design choices:
Parse timestamps from all commits on clone into a local commit index, then maintain that index through subsequent commits and syncs.
Use an indexed SQL
ORDER BY
query to match timestamps to commit IDs for a fast and consistent result.Round incomplete timestamp strings up using rules consistent across computers and local time of day.
Case Study 2: Multiple "origin" Servers
Now let us consider a common use case at the time of this writing — during the COVID-19 pandemic — where you’re working from home a lot, going into the office one part-day a week only to do things that have to be done on-site at the office. Let us also say you have no remote access back into the work LAN, such as because your site IT is paranoid about security. You may still want off-machine backups of your commits while working from home, so you need the ability to quickly switch between the “home” and “work” remote repositories, with your laptop acting as a kind of sneakernet link between the big development server at the office and your family’s home NAS.
Git Method
We first need to clone the work repo down to our laptop, so we can work on it at home:
git clone https://dev-server.example.com/repo
cd repo
git remote rename origin work
The last command is optional, strictly speaking. We could continue to
use Git’s default name for the work repo’s origin — sensibly enough
called “origin
” — but it makes later commands harder to understand, so
we rename it here. This will also make the parallel with Fossil easier
to draw.
The first time we go home after this, we have to reverse-clone the work repo up to the NAS:
ssh my-nas.local 'git init --bare /SHARES/dayjob/repo.git'
git push --all ssh://my-nas.local//SHARES/dayjob/repo.git
Realize that this is carefully optimized down to these two long
commands. In practice, we’d expect a user typing these commands by hand from memory
to need to give four or more commands here instead.
Packing the “git init
” call into the “ssh
” call is something more
often done in scripts and documentation examples than done interactively,
which then necessitates a third command before the push, “exit
”.
There’s also a good chance that you’ll forget the need for the --bare
option here to avoid a fatal complaint from Git that the laptop can’t
push into a non-empty repo. If you fall into this trap, among the many
that Git lays for newbies, you have to nuke the incorrectly initted
repo, search the web or Git man pages to find out about --bare
, and try again.
Having navigated that little minefield, we can tell Git that there is a second origin, a “home” repo in addition to the named “work” repo we set up earlier:
git remote add home ssh://my-nas.local//SHARES/dayjob/repo.git
git config master.remote home
We don’t have to push or pull because the remote repo is a complete clone of the repo on the laptop at this point, so we can just get to work now, committing along the way to get our work safely off-machine and onto our home NAS, like so:
git add
git commit
git push
We didn’t need to give a remote name on the push because we told it the new upstream is the home NAS earlier.
Now Friday comes along, and one of your office-mates needs a feature you’re working on. You agree to come into the office later that afternoon to sync up via the dev server:
git push work master # send your changes from home up
git pull work master # get your coworkers’ changes
Alternately, we could add “--set-upstream/-u work
” to the first
command if we were coming into work long enough to do several Git-based things, not just pop in and sync.
That would allow the second to be just “git pull
”, but the cost is
that when returning home, you’d have to manually reset the upstream
again.
This example also shows a consequence of that fact that Git doesn’t sync branch names: you have to keep repeating yourself like an obsequious supplicant: “Master, master.” Didn’t we invent computers to serve humans, rather than the other way around?
Fossil Method
Now we’re going to do the same thing using Fossil, with the commands arranged in blocks corresponding to those above for comparison.
We start the same way, cloning the work repo down to the laptop:
fossil clone https://dev-server.example.com/repo
cd repo
fossil remote add work https://dev-server.example.com/repo
We’ve chosen the new “fossil clone URI
” syntax added in Fossil 2.14 rather than separate
clone
and open
commands to make the parallel with Git clearer. See
above for more on that topic.
Our remote
command is longer than the Git equivalent because
Fossil currently has no short command
to rename an existing remote. Worse, unlike with Git, we can’t just keep
using the default remote name because Fossil uses that slot in its
configuration database to store the current remote name, so on
switching from work to home, the home URL will overwrite the work URL if
we don’t give it an explicit name first.
Although the Fossil commands are longer, so far, keep it in perspective: they’re one-time setup costs, easily amortized to insignificance by the shorter day-to-day commands below.
On first beginning to work from home, we reverse-clone the Fossil repo up to the NAS:
rsync repo.fossil my-nas.local:/SHARES/dayjob/
Now we’re beginning to see the advantage of Fossil’s simpler model,
relative to the tricky “git init && git push
” sequence above.
Fossil’s alternative is almost impossible to get
wrong: copy this to that. Done.
We’re relying on the rsync
feature that creates up to one level of
missing directory (here, dayjob/
) on the remote. If you know in
advance that the remote directory already exists, you could use a
slightly shorter scp
command instead. Even with the extra 2 characters
in the rsync
form, it’s much shorter because a Fossil repository is a
single SQLite database file, not a tree containing a pile of assorted
files. Because of this, it works reliably without any of the caveats
inherent in using rsync
to clone a Git repo.
Now we set up the second remote, which is again simpler in the Fossil case:
fossil remote add home ssh://my-nas.local//SHARES/dayjob/repo.fossil
fossil remote home
The first command is nearly identical to the Git version, but the second
is considerably simpler. And to be fair, you won’t find the
“git config
” command above in all Git tutorials. The more common
alternative we found with web searches is even longer:
“git push --set-upstream home master
”.
Where Fossil really wins is in the next step, making the initial commit from home:
fossil ci
It’s one short command for Fossil instead of three for Git — or two if
you abbreviate it as “git commit -a && git push
” — because of Fossil’s
autosync feature feature and deliberate omission of a
staging feature.
The “Friday afternoon sync-up” case is simpler, too:
fossil remote work
fossil sync
Back at home, it’s simpler still: we may be able to do away with the second command,
saying just “fossil remote home
” because the sync will happen as part
of the next commit, thanks once again to Fossil’s autosync feature. If
the working branch now has commits from other developers after syncing
with the central repository, though, you’ll want to say “fossil up
” to
avoid creating an inadvertent fork in the branch.
(Which is easy to fix if it occurs: fossil merge
without arguments
means “merge open tips on the current branch.”)