Git - Update Operation

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Modify existing function

Tom performs clone operation and after that sees new file string.c and he wanted to know who added this file to the repository ? And for what purpose ? So he executes git log command.

[tom@CentOS ~]$ git clone gituser@git.server.com:project.git

Above command will produce the following result:

Initialized empty Git repository in /home/tom/project/.git/
remote: Counting objects: 6, done.
remote: Compressing objects: 100% (4/4), done.
Receiving objects: 100% (6/6), 726 bytes, done.
remote: Total 6 (delta 0), reused 0 (delta 0)

Clone operation will create new directory inside current working directory. He changes directory to newly created directory and executes git log command.

[tom@CentOS ~]$ cd project/

[tom@CentOS project]$ git log

Above command will produce the following result:

commit d1e19d316224cddc437e3ed34ec3c931ad803958
Author: Jerry Mouse <jerry@tutorialspoint.com>
Date: Wed Sep 11 08:05:26 2013 +0530

Changed return type of my_strlen to size_t


commit 19ae20683fc460db7d127cf201a1429523b0e319
Author: Tom Cat <tom@tutorialspoint.com>
Date: Wed Sep 11 07:32:56 2013 +0530

Initial commit

After observing log, he realizes that string.c file was added by Jerry to implement basic string operations. He is curious about Jerry’s code. So he opens string.c file in text editor and immediately finds a bug. In my_strlen function, Jerry is not using constant pointer. So he decides to modify Jerry’s code. After modification code will look like this.

[tom@CentOS project]$ git diff

Above command will produce the following result:

diff --git a/string.c b/string.c
index 7da2992..32489eb 100644
--- a/string.c
+++ b/string.c
@@ -1,8 +1,8 @@
#include 
-size_t my_strlen(char *s)
+size_t my_strlen(const char *s)
{
- char *p = s;
+ const char *p = s;
while (*p)
++p;

After testing, he commits his change.

[tom@CentOS project]$ git status -s
M string.c
?? string

[tom@CentOS project]$ git add string.c

[tom@CentOS project]$ git commit -m 'Changed char pointer to const char pointer'
[master cea2c00] Changed char pointer to const char pointer
1 files changed, 2 insertions(+), 2 deletions(-)

[tom@CentOS project]$ git log

Above command will produce the following result:

commit cea2c000f53ba99508c5959e3e12fff493b
Author: Tom Cat <tom@tutorialspoint.com>
Date: Wed Sep 11 08:32:07 2013 +0530

Changed char pointer to const char pointer


commit d1e19d316224cddc437e3ed34ec3c931ad803958
Author: Jerry Mouse <jerry@tutorialspoint.com>
Date: Wed Sep 11 08:05:26 2013 +0530

Changed return type of my_strlen to size_t


commit 19ae20683fc460db7d127cf201a1429523b0e319
Author: Tom Cat <tom@tutorialspoint.com>
Date: Wed Sep 11 07:32:56 2013 +0530
Initial commit

Tom uses git push command to push his changes.

[tom@CentOS project]$ git push origin master

Above command will produce the following result:

Counting objects: 5, done.
Compressing objects: 100% (3/3), done.
Writing objects: 100% (3/3), 336 bytes, done.
Total 3 (delta 1), reused 0 (delta 0)
To gituser@git.server.com:project.git
d1e19d3..cea2c00 master −> master

Add new function

Meanwhile, Jerry decides to implement string compare functionality. So he modifies string.c file. After modification, file will look like this:

[jerry@CentOS project]$ git diff

Above command will produce the following result:

index 7da2992..bc864ed 100644
--- a/string.c
+++ b/string.c
30Git Tutorials
@@ -9,9 +9,20 @@ size_t my_strlen(char *s)
return (p -s );
}
+char *my_strcpy(char *t, char *s)
+{
+
char *p = t;
+
+ while (*t++ = *s++)
+ ;
+
+
return p;
+}
+
int main(void)
{
int i;
+
char p1[32];
char *s[] = {
"Git tutorials",
"Tutorials Point"
@@ -20,5 +31,7 @@ int main(void)
for (i = 0; i < 2; ++i)
printf("string lenght of %s = %lu\n", s[i], my_strlen(s[i]));
+
printf("%s\n", my_strcpy(p1, "Hello, World !!!"));
+
return 0;
}

After testing, he is ready to push his change.

[jerry@CentOS project]$ git status -s
M string.c
?? string

[jerry@CentOS project]$ git add string.c

[jerry@CentOS project]$ git commit -m "Added my_strcpy function"
[master e944e5a] Added my_strcpy function
1 files changed, 13 insertions(+), 0 deletions(-)

Before push operation, he verifies commit by viewing log messages.

[jerry@CentOS project]$ git log

Above command will produce the following result:

commit e944e5aab74b26e7447d3281b225309e4e59efcd
Author: Jerry Mouse <jerry@tutorialspoint.com>
Date: Wed Sep 11 08:41:42 2013 +0530

Added my_strcpy function


commit d1e19d316224cddc437e3ed34ec3c931ad803958
Author: Jerry Mouse <jerry@tutorialspoint.com>
Date: Wed Sep 11 08:05:26 2013 +0530

Changed return type of my_strlen to size_t


commit 19ae20683fc460db7d127cf201a1429523b0e319
Author: Tom Cat <tom@tutorialspoint.com>
Date: Wed Sep 11 07:32:56 2013 +0530

Initial commit

Jerry is happy with changes and he wants to push his changes.

[jerry@CentOS project]$ git push origin master

Above command will produce the following result:

To gituser@git.server.com:project.git
! [rejected]
master −> master (non-fast-forward)
error: failed to push some refs to 'gituser@git.server.com:project.git'
To prevent you from losing history, non-fast-forward updates were rejected
Merge the remote changes before pushing again. See the 'Note about
fast-forwards' section of 'git push --help' for details.

But Git is not allowing Jerry to push his changes. Because Git identified that remote repository and Jerry’s local repository is not in sync. Because of this, he can lose history of project. So to avoid this mess Git failed this operation. Now, Jerry has to first update its local repository and then only he can push his own changes.

Fetch latest changes

Jerry executes git pull command to synchronize his local repository with remote one.

[jerry@CentOS project]$ git pull

Above command will produce the following result:

remote: Counting objects: 5, done.
remote: Compressing objects: 100% (3/3), done.
remote: Total 3 (delta 1), reused 0 (delta 0)
Unpacking objects: 100% (3/3), done.
From git.server.com:project
d1e19d3..cea2c00 master −> origin/master
First, rewinding head to replay your work on top of it...
Applying: Added my_strcpy function

After pull operation, Jerry checks the log messages and finds the details of Tom’s commit with commit ID cea2c000f53ba99508c5959e3e12fff493ba6f69

[jerry@CentOS project]$ git log

Above command will produce the following result:

commit e86f0621c2a3f68190bba633a9fe6c57c94f8e4f
Author: Jerry Mouse <jerry@tutorialspoint.com>
Date: Wed Sep 11 08:41:42 2013 +0530

Added my_strcpy function


commit cea2c000f53ba99508c5959e3e12fff493ba6f69
Author: Tom Cat <tom@tutorialspoint.com>
Date: Wed Sep 11 08:32:07 2013 +0530

Changed char pointer to const char pointer


commit d1e19d316224cddc437e3ed34ec3c931ad803958
Author: Jerry Mouse <jerry@tutorialspoint.com>
Date: Wed Sep 11 08:05:26 2013 +0530

Changed return type of my_strlen to size_t


commit 19ae20683fc460db7d127cf201a1429523b0e319
Author: Tom Cat <tom@tutorialspoint.com>
Date: Wed Sep 11 07:32:56 2013 +0530
Initial commit

Now, Jerry’s local repository is fully synchronized with the remote repository. So he can safely push his changes.

[jerry@CentOS project]$ git push origin master

Above command will produce the following result:

Counting objects: 5, done.
Compressing objects: 100% (3/3), done.
Writing objects: 100% (3/3), 455 bytes, done.
Total 3 (delta 1), reused 0 (delta 0)
To gituser@git.server.com:project.git
cea2c00..e86f062 master −> master


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