## knowledge gained from learning git.

# If you inadvertently remove a file of your working copy. Don't worry. Git are good at recovering old versions of files, such as:
$git checkout HEAD — data # show what the file looks like in a certain branch.$git show branch_name:file_name

# In newer versions of Git, git diff –ours is a synonym for git diff HEAD, because it shows the differences between "our" version and the merged version. Similarly, git diff MERGE_HEAD can be written as git diff –theirs. You can use git diff –base to see the combined set of changes since the merge base, which would otherwise be rather awkwardly written as:
git diff $(git merge-base HEAD MERGE_HEAD) # While you are in the process of resolving a conflict, you can use some special git log options to help you figure out exactly where the changes came from and why. Try this:$git log –merge –left-right -p
–merge shows only commits related to files that produced a conflict.
–left-right displays < if the commit was from the "left" side of the merge("our version", the one you started with), or > if the commit was from the "right" side of the merge("their" version, the one you're merging in).
-p shows the commit message and the patch associated with each commit.

If your repository were more complicated and several files had conflicts, you could also provide the exact file names you are interested in as a command line option, like this:
$git log –merge –left-right -p hello # The -s option to git ls-files shows all the files with all stages. If you want to see only conflicted files, use the -u option instead. #$ git checkout -m branch_name
If possible or if specifically requested with the -m option, Git attempts to carry your local change into the new working directory by performing a merge operation between your local modifications and the target branch.

# $git reset –hard ORIG_HEAD If you want to abort or discard the merge after it has finished(that is,after it has introduced a new merge commit), use the above command. Prior to beginning the merge operation, Git saves your original branch HEAD in the ORIG_HEAD ref for just this sort of purpose. You should be very careful here, though. If you did not start the merge with a clean working directory and index, you could geet in trouble and lose any uncommitted changes you have in your directory. # Just show what the file looks like in a branch.$ git show branch_name:file_name

# The command for manipulating remotes is git remote. This operation introduces a few new settings in the .git/config file.

## Diff, Patch, and Friends(diff, patch和他们的相关工具)(第二篇)

Use the diff program to avoid eyestrain and insanity:

diff -u 1 2
— 1 Sat Apr 20 22:11:53 1996
+++ 2 Sat Apr 20 22:12:01 1996
-1,9 +1,9
Ecce Eduardus Ursus scalis nunc tump-tump-tump
occipite gradus pulsante post Christophorum
Robinum descendens. Est quod sciat unus et solus
-modus gradibus desendendi, non nunquam autem
+modus gradibus descendendi, nonnunquam autem
sentit, etiam alterum modum exstare, dummodo
-pulsationibus desinere et de no modo meditari
+pulsationibus desinere et de eo modo meditari
possit. Deinde censet alios modos non esse. En,
nunc ipse in imo est, vobis ostentari paratus.
Winnie ille Pu.

There are several things to notice here:

*

The file names and last dates of modification are shown in a “header” at the top. The dates may not mean anything if you are comparing files that have been passed back and forth by e-mail, but they become very useful in other circumstances.

*

The file names (in this case, 1 and 2—are preceded by — and +++.

*

After the header comes a line that includes numbers. We will discuss that line later.

*

The lines that did not change between files are shown preceded by spaces; those that are different in the different files are shown preceded by a character which shows which file they came from. Lines which exist only in a file whose name is preceded by — in the header are preceded by a – character, and vice-versa for lines preceded by a + character. Another way to remember this is to see that the lines preceded by a – character were removed from the first (—) file, and those preceded by a + character were added to the second (+++) file.

*

Three spelling changes have been made: “desendendi” has been corrected to “descendendi”, “non nunquam” has been corrected to “nonnunquam”, and “no” has been corrected to “eo”.

Perhaps the main thing to notice is that you didn't need this description of how to interpret diff's output in order to find the differences. It is rather easy to compare two adjacent lines and see the differences.

It's not always this easy

Unfortunately, if too many adjacent lines have been changed, interpretation isn't as immediately obvious; but by knowing that each marked line has been changed in some way, you can figure it out. For instance, in this comparison, where the file 3 contains the damaged contents, and file 4 (identical to file 2 in the previous example) contains the correct contents, three lines in a row are changed, and now each line with a difference is not shown directly above the corrected line:

diff -u 3 4
— 3 Sun Apr 21 18:57:08 1996
+++ 4 Sun Apr 21 18:56:45 1996
-1,9 +1,9
Ecce Eduardus Ursus scalis nunc tump-tump-tump
occipite gradus pulsante post Christophorum
Robinum descendens. Est quod sciat unus et solus
-modus gradibus desendendi, non nunquam autem
-sentit, etiam alterum nodum exitare, dummodo
-pulsationibus desinere et de no modo meditari
+modus gradibus descendendi, nonnunquam autem
+sentit, etiam alterum modum exstare, dummodo
+pulsationibus desinere et de eo modo meditari
possit. Deinde censet alios modos non esse. En,
nunc ipse in imo est, vobis ostentari paratus.
Winnie ille Pu.

It takes a little more work to find the added mistakes; “nodum” for “modum” and “exitare” for “exstare”. Imagine if 50 lines in a row had each had a one-character change, though. This begins to resemble the old job of going through the whole file, character-by-character, looking for changes. All we've done is (potentially) shrink the amount of comparison you have to do.

Fortunately, there are several tools for finding these kinds of differences more easily. GNU Emacs has “word diff” functionality. There is also a GNU “wdiff” program which helps you find these kinds of differences without using Emacs.

Let's look first at GNU Emacs. For this example, files 5 and 6 are exactly the same, respectively, as files 3 and 4 before. I bring up emacs under X (which provides me with colored text), and type:

M-x ediff-files RET
5 RET
6 RET

In the new window which pops up, I press the space bar, which tells Emacs to highlight the differences. Look at Figure 1 and see how easy it is to find each changed word.

Figure 1. ediff-files 5 6

GNU wdiff is also very useful, especially if you aren't running X. A pager (such as less) is all that is required—and that is only required for large differences. The exact same set of files (5 and 6), compared with the command wdiff -t 5 6, is shown in Figure 2.
GNU wdiff也很有用，特别是你没有运行X服务的时候。一个分屏工具(比如 less)就足够用来查找大范围的差异了。

Figure 2. wdiff -t 5 6

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