$ echo 'hello world' > file.txt
$ git add .
$ git commit -a -m "initial commit"
-Created initial commit 54196cc2703dc165cbd373a65a4dcf22d50ae7f7
+[master (root-commit) 54196cc] initial commit
+ 1 files changed, 1 insertions(+), 0 deletions(-)
create mode 100644 file.txt
$ echo 'hello world!' >file.txt
$ git commit -a -m "add emphasis"
-Created commit c4d59f390b9cfd4318117afde11d601c1085f241
+[master c4d59f3] add emphasis
+ 1 files changed, 1 insertions(+), 1 deletions(-)
------------------------------------------------
-What are the 40 digits of hex that git responded to the commit with?
+What are the 7 digits of hex that git responded to the commit with?
We saw in part one of the tutorial that commits have names like this.
It turns out that every object in the git history is stored under
-such a 40-digit hex name. That name is the SHA1 hash of the object's
+a 40-digit hex name. That name is the SHA1 hash of the object's
contents; among other things, this ensures that git will never store
the same data twice (since identical data is given an identical SHA1
name), and that the contents of a git object will never change (since
-that would change the object's name as well).
+that would change the object's name as well). The 7 char hex strings
+here are simply the abbreviation of such 40 character long strings.
+Abbreviations can be used everywhere where the 40 character strings
+can be used, so long as they are unambiguous.
It is expected that the content of the commit object you created while
following the example above generates a different SHA1 hash than
the one shown above because the commit object records the time when
it was created and the name of the person performing the commit.
-We can ask git about this particular object with the cat-file
+We can ask git about this particular object with the `cat-file`
command. Don't copy the 40 hex digits from this example but use those
from your own version. Note that you can shorten it to only a few
characters to save yourself typing all 40 hex digits:
The index file
--------------
-The primary tool we've been using to create commits is "git-commit
--a", which creates a commit including every change you've made to
+The primary tool we've been using to create commits is `git-commit
+-a`, which creates a commit including every change you've made to
your working tree. But what if you want to commit changes only to
certain files? Or only certain changes to certain files?
+hello world, again
------------------------------------------------
-So "git-diff" is comparing against something other than the head.
+So 'git-diff' is comparing against something other than the head.
The thing that it's comparing against is actually the index file,
which is stored in .git/index in a binary format, but whose contents
we can examine with ls-files:
hello world, again
------------------------------------------------
-So what our "git-add" did was store a new blob and then put
+So what our 'git-add' did was store a new blob and then put
a reference to it in the index file. If we modify the file again,
-we'll see that the new modifications are reflected in the "git-diff"
+we'll see that the new modifications are reflected in the 'git-diff'
output:
------------------------------------------------
+again?
------------------------------------------------
-With the right arguments, git-diff can also show us the difference
+With the right arguments, 'git-diff' can also show us the difference
between the working directory and the last commit, or between the
index and the last commit:
+hello world, again
------------------------------------------------
-At any time, we can create a new commit using "git-commit" (without
-the -a option), and verify that the state committed only includes the
+At any time, we can create a new commit using 'git-commit' (without
+the "-a" option), and verify that the state committed only includes the
changes stored in the index file, not the additional change that is
still only in our working tree:
+again?
------------------------------------------------
-So by default "git-commit" uses the index to create the commit, not
-the working tree; the -a option to commit tells it to first update
+So by default 'git-commit' uses the index to create the commit, not
+the working tree; the "-a" option to commit tells it to first update
the index with all changes in the working tree.
-Finally, it's worth looking at the effect of "git-add" on the index
+Finally, it's worth looking at the effect of 'git-add' on the index
file:
------------------------------------------------
$ git add closing.txt
------------------------------------------------
-The effect of the "git-add" was to add one entry to the index file:
+The effect of the 'git-add' was to add one entry to the index file:
------------------------------------------------
$ git ls-files --stage
commit" would create a commit that added closing.txt (with its new
contents), but that didn't modify file.txt.
-Also, note that a bare "git diff" shows the changes to file.txt, but
+Also, note that a bare `git diff` shows the changes to file.txt, but
not the addition of closing.txt, because the version of closing.txt
in the index file is identical to the one in the working directory.
linkgit:gitcvs-migration[7],
linkgit:gitcore-tutorial[7],
linkgit:gitglossary[7],
+linkgit:git-help[1],
link:everyday.html[Everyday git],
link:user-manual.html[The Git User's Manual]