| blob | 3e87ba40421fd53b4a629d0a870acd3ae7d0d470 |
4 <head>
8 /* Debug borders */
10 /*
11 border: 1px solid red;
12 */
13 }
15 body {
17 }
19 a {
22 }
25 }
27 em {
29 }
31 strong {
33 }
35 tt {
37 }
45 }
49 }
50 h2 {
52 }
53 h3 {
55 }
56 h3 + * {
58 }
63 }
65 hr {
67 }
69 p {
72 }
74 pre {
77 }
79 span#author {
84 }
85 span#email {
86 }
87 span#revision {
89 }
91 div#footer {
97 }
98 div#footer-text {
101 }
102 div#footer-badges {
105 }
107 div#preamble,
114 }
118 }
122 }
124 /* Block element titles. */
131 }
134 }
138 }
141 }
144 }
150 }
154 }
159 }
163 }
167 }
170 }
179 }
183 }
188 }
192 }
198 dl {
201 }
202 dt {
206 }
209 }
213 }
216 }
220 }
221 thead {
224 }
225 tfoot {
227 }
232 }
235 }
240 }
243 }
247 }
249 div#toctitle {
256 }
261 }
265 }
269 }
273 }
275 /* Workarounds for IE6's broken and incomplete CSS2. */
281 }
287 }
293 }
297 }
302 }
304 /* IE6 sets dynamically generated links as visited. */
306 </style>
308 </head>
309 <body>
311 <h1>
313 </h1>
317 A tutorial introduction to git: part two
318 </p>
319 </div>
320 </div>
324 </div>
327 <div class="para"><p>You should work through <a href="gittutorial.html">gittutorial(7)</a> before reading this tutorial.</p></div>
329 git's architecture--the object database and the index file--and to
330 provide the reader with everything necessary to understand the rest
331 of the git documentation.</p></div>
332 </div>
338 <pre><tt>$ mkdir test-project
339 $ cd test-project
340 $ git init
341 Initialized empty Git repository in .git/
342 $ echo 'hello world' > file.txt
343 $ git add .
344 $ git commit -a -m "initial commit"
345 [master (root-commit) 54196cc] initial commit
347 create mode 100644 file.txt
348 $ echo 'hello world!' >file.txt
349 $ git commit -a -m "add emphasis"
350 [master c4d59f3] add emphasis
352 </div></div>
353 <div class="para"><p>What are the 7 digits of hex that git responded to the commit with?</p></div>
355 It turns out that every object in the git history is stored under
356 a 40-digit hex name. That name is the SHA1 hash of the object's
357 contents; among other things, this ensures that git will never store
358 the same data twice (since identical data is given an identical SHA1
359 name), and that the contents of a git object will never change (since
360 that would change the object's name as well). The 7 char hex strings
361 here are simply the abbreviation of such 40 character long strings.
362 Abbreviations can be used everywhere where the 40 character strings
363 can be used, so long as they are unambiguous.</p></div>
365 following the example above generates a different SHA1 hash than
366 the one shown above because the commit object records the time when
367 it was created and the name of the person performing the commit.</p></div>
369 command. Don't copy the 40 hex digits from this example but use those
370 from your own version. Note that you can shorten it to only a few
375 commit
376 $ git cat-file commit 54196cc2
377 tree 92b8b694ffb1675e5975148e1121810081dbdffe
381 initial commit</tt></pre>
382 </div></div>
384 a file. In addition, a tree can also refer to other tree objects,
385 thus creating a directory hierarchy. You can examine the contents of
386 any tree using ls-tree (remember that a long enough initial portion
387 of the SHA1 will also work):</p></div>
392 </div></div>
394 reference to that file's data:</p></div>
398 blob</tt></pre>
399 </div></div>
400 <div class="para"><p>A "blob" is just file data, which we can also examine with cat-file:</p></div>
404 hello world</tt></pre>
405 </div></div>
407 its response to the initial tree was a tree with a snapshot of the
408 directory state that was recorded by the first commit.</p></div>
410 directory:</p></div>
413 <pre><tt>$ find .git/objects/
414 .git/objects/
415 .git/objects/pack
416 .git/objects/info
417 .git/objects/3b
419 .git/objects/92
420 .git/objects/92/b8b694ffb1675e5975148e1121810081dbdffe
421 .git/objects/54
423 .git/objects/a0
424 .git/objects/a0/423896973644771497bdc03eb99d5281615b51
425 .git/objects/d0
426 .git/objects/d0/492b368b66bdabf2ac1fd8c92b39d3db916e59
427 .git/objects/c4
428 .git/objects/c4/d59f390b9cfd4318117afde11d601c1085f241</tt></pre>
429 </div></div>
431 header identifying their length and their type. The type is either a
432 blob, a tree, a commit, or a tag.</p></div>
434 from .git/HEAD:</p></div>
437 <pre><tt>$ cat .git/HEAD
438 ref: refs/heads/master</tt></pre>
439 </div></div>
441 tells us this by naming a file under the .git directory, which itself
442 contains a SHA1 name referring to a commit object, which we can
443 examine with cat-file:</p></div>
446 <pre><tt>$ cat .git/refs/heads/master
447 c4d59f390b9cfd4318117afde11d601c1085f241
448 $ git cat-file -t c4d59f39
449 commit
450 $ git cat-file commit c4d59f39
451 tree d0492b368b66bdabf2ac1fd8c92b39d3db916e59
452 parent 54196cc2703dc165cbd373a65a4dcf22d50ae7f7
456 add emphasis</tt></pre>
457 </div></div>
461 <pre><tt>$ git ls-tree d0492b36
462 100644 blob a0423896973644771497bdc03eb99d5281615b51 file.txt
463 $ git cat-file blob a0423896
464 hello world!</tt></pre>
465 </div></div>
470 tree 92b8b694ffb1675e5975148e1121810081dbdffe
474 initial commit</tt></pre>
475 </div></div>
477 unusual in that it lacks any parent.</p></div>
479 to have multiple parents. In that case the commit represents a
480 merge, with the parent references pointing to the heads of the merged
481 branches.</p></div>
484 for details.</p></div>
486 project's history:</p></div>
488 <li>
489 <p>
491 snapshot of a directory tree at a particular point in the
492 history, and refer to "parent" commits to show how they're
493 connected into the project history.
494 </p>
495 </li>
496 <li>
497 <p>
498 "tree" objects represent the state of a single directory,
499 associating directory names to "blob" objects containing file
500 data and "tree" objects containing subdirectory information.
501 </p>
502 </li>
503 <li>
504 <p>
505 "blob" objects contain file data without any other structure.
506 </p>
507 </li>
508 <li>
509 <p>
510 References to commit objects at the head of each branch are
511 stored in files under .git/refs/heads/.
512 </p>
513 </li>
514 <li>
515 <p>
516 The name of the current branch is stored in .git/HEAD.
517 </p>
518 </li>
519 </ul></div>
521 But as we can see above, a tree can be referred to in many different
522 ways--by the SHA1 name for that tree, by the name of a commit that
523 refers to the tree, by the name of a branch whose head refers to that
524 tree, etc.--and most such commands can accept any of these names.</p></div>
526 designate such an argument.</p></div>
527 </div>
531 -a</tt>, which creates a commit including every change you've made to
532 your working tree. But what if you want to commit changes only to
533 certain files? Or only certain changes to certain files?</p></div>
535 that there are more flexible ways creating commits.</p></div>
540 </div></div>
542 intermediate step, and ask for diffs along the way to keep track of
543 what's happening:</p></div>
546 <pre><tt>$ git diff
547 --- a/file.txt
548 +++ b/file.txt
550 hello world!
551 +hello world, again
552 $ git add file.txt
553 $ git diff</tt></pre>
554 </div></div>
556 head still doesn't contain the new line:</p></div>
559 <pre><tt>$ git diff HEAD
560 diff --git a/file.txt b/file.txt
562 --- a/file.txt
563 +++ b/file.txt
565 hello world!
566 +hello world, again</tt></pre>
567 </div></div>
569 The thing that it's comparing against is actually the index file,
570 which is stored in .git/index in a binary format, but whose contents
571 we can examine with ls-files:</p></div>
574 <pre><tt>$ git ls-files --stage
576 $ git cat-file -t 513feba2
577 blob
578 $ git cat-file blob 513feba2
579 hello world!
580 hello world, again</tt></pre>
581 </div></div>
583 a reference to it in the index file. If we modify the file again,
585 output:</p></div>
589 $ git diff
591 --- a/file.txt
592 +++ b/file.txt
594 hello world!
595 hello world, again
596 +again?</tt></pre>
597 </div></div>
598 <div class="para"><p>With the right arguments, <em>git diff</em> can also show us the difference
599 between the working directory and the last commit, or between the
600 index and the last commit:</p></div>
603 <pre><tt>$ git diff HEAD
604 diff --git a/file.txt b/file.txt
605 index a042389..ba3da7b 100644
606 --- a/file.txt
607 +++ b/file.txt
609 hello world!
610 +hello world, again
611 +again?
612 $ git diff --cached
613 diff --git a/file.txt b/file.txt
615 --- a/file.txt
616 +++ b/file.txt
618 hello world!
619 +hello world, again</tt></pre>
620 </div></div>
622 the "-a" option), and verify that the state committed only includes the
623 changes stored in the index file, not the additional change that is
624 still only in our working tree:</p></div>
628 $ git diff HEAD
629 diff --git a/file.txt b/file.txt
631 --- a/file.txt
632 +++ b/file.txt
634 hello world!
635 hello world, again
636 +again?</tt></pre>
637 </div></div>
639 the working tree; the "-a" option to commit tells it to first update
640 the index with all changes in the working tree.</p></div>
642 file:</p></div>
646 $ git add closing.txt</tt></pre>
647 </div></div>
648 <div class="para"><p>The effect of the <em>git add</em> was to add one entry to the index file:</p></div>
651 <pre><tt>$ git ls-files --stage
654 </div></div>
656 current contents of the file:</p></div>
660 goodbye, world</tt></pre>
661 </div></div>
663 situation:</p></div>
666 <pre><tt>$ git status
667 # On branch master
668 # Changes to be committed:
669 # (use "git reset HEAD <file>..." to unstage)
670 #
671 # new file: closing.txt
672 #
673 # Changed but not updated:
674 # (use "git add <file>..." to update what will be committed)
675 #
676 # modified: file.txt
677 #</tt></pre>
678 </div></div>
680 it is listed as "Changes to be committed". Since file.txt has
681 changes in the working directory that aren't reflected in the index,
683 commit" would create a commit that added closing.txt (with its new
684 contents), but that didn't modify file.txt.</p></div>
685 <div class="para"><p>Also, note that a bare <tt>git diff</tt> shows the changes to file.txt, but
686 not the addition of closing.txt, because the version of closing.txt
687 in the index file is identical to the one in the working directory.</p></div>
689 is also populated from the object database when checking out a
690 branch, and is used to hold the trees involved in a merge operation.
692 pages for details.</p></div>
693 </div>
697 pages for any of the git commands; one good place to start would be
699 should be able to find any unknown jargon in <a href="gitglossary.html">gitglossary(7)</a>.</p></div>
701 comprehensive introduction to git.</p></div>
703 import a CVS repository into git, and shows how to use git in a
704 CVS-like way.</p></div>
707 <div class="para"><p>For git developers, <a href="gitcore-tutorial.html">gitcore-tutorial(7)</a> goes
708 into detail on the lower-level git mechanisms involved in, for
709 example, creating a new commit.</p></div>
710 </div>
720 </div>
724 </div>
728 </div>
729 </div>
730 </body>
731 </html>