Lecture1 Shell

1.common command:

  • date
  • echo:
    1.usage: prints out the argument you given and space can separate different arguments
    2.echo $PATH：present all paths executable
    which echo: find out which file is executed
  • path related
    cd: change to another path
    pwd: see the current path
    “..” refers to parent directory
    “.” refers to current directory
    ls: see what is stored in a given directory

  • cp: copy a file (when copy a folder use -r)
    mv: move a file
    mkdir: create a directory
    touch: create a file
    cat: display the content of the file
    rm: delete the file (when delete a folder apply “-r”, can apply *)
    vim: open a text editor

  • redirect your input and output:
    < file : rewire you input (将输入重定向)
    > file : rewire your output(将输出结果重定向)
    >> append a file
    | : take the output of the former as the input of the later( chain programs together)
  • root
    sudo: (super user do)
    permission class:
    owner文件所有者, group用户组, other user其他用户
    chmod: rwx(八进制数字模式)
  • 2.Basic knowledge
  • path:
    The location of your targeted file, separated by “/” for linux and “\“for windows
    / represents root (For windows it might be like C:\ )
    1.absolute path and relative path
    absolute path: begin with root
  • flag and options:
    flag: begin with “-“ can modify the behaviour of the command
    options: flags with values
    >
    >r w x: (read write and execute)different permissions:
    > Above, only the owner is allowed to modify (w) the missing directory (i.e., add/remove files in it). To enter a directory, a user must have “search” (represented by “execute”: x) permissions on that directory (and its parents). To list its contents, a user must have read (r) permissions on that directory.

Lecture2 Version control

1.Data model -> recursive structure

  • folders -> trees, files -> blogs
  • A direction graph without loops
  • Metadata: every snapshot has metadata including the submission date and the user who submitted it

2.Principle:
Take a snapshot at a certain time, recording all the information

3.Lower level->actual data structure
Notice: The trees, snapshots and blob are just pointers, and hash values are also pointers

  • blob : file an array of bytes
  • tree: mapping from the filename or the directoryname to the actual content( tree or file)
  • snapshots: commits, including parents( an array of previous commits), author and a message
    The actual content of a snapshot is a tree
  • objects:
    The actual content of your repository
  • references: map from<strings,strings>
    With references, you can easily name a certain snapshot.(Without considering the long hash values)
    The mapping relationship can be changed.
  • branch
    • master: default branch when you initialized a git repository, often refer to the most up-to-date version of your project. Usually it is a pointer to the latest commit.
    • head: where you currently looking right now

4.git command

  • git init
    It can initialize the reposiotry for git.
    And apply “ls .git” you could see the disk area containing objects and references…
  • git help
    list the helpful command line
  • git status
    check the current status
  • git cat-file -p <hash value>
    look the what contains in the location that this hash value points

  • git add
    Track the file in the next snapshot, if you don’t apply “add”, the changes will be untracked
    It can employ the staging area and has more flexibility to add commit history
    git add -p <file> : track the file by pieces

  • git commit -m “information”
    Take a snapshot of the tracked changes, information can inform the readers
    git commit -a: commit all tracked files

  • git log
    Visualize the commit graph
    Powerful arguments: git log –all –graph –decorate

  • git checkout
    Help you move around in your version history, moves the head pointer (different bracnches)
    This can help you change your working projects flow

  • git diff
    Compare the difference from last commit of a certain file(you can also specify the version by adding arguments)

  • git branch:
    • Without an argument: list the current branches
    • Followed by a file name: create a new branch
    • git branch -vv: detailed information

  • git merge:
    A powerful command that can help you merge different versions of snapshots together. Usually, it will merge the branch to your main branch.
    Notice: If there are versions conflicts between the branches, the programmers should solve this issue

  • git remote
    list all the remote repositories that git knows for our local repository
    • git remote add <name> <url> (If there is only one remote, it is called origin by convention)
    • git push(help your repository interact worth the remote repository)
      git push <remote> <local branch>:<remote branch>
    • git branch –set-upstream-to=<remote>/<branch>
      Create a mapping between your local checking branch to the remote set branch
    • git fetch: retrieving changes to a repository that are present on a remote and getting the changes on your local machine
    • git pull
      Similar to “git fetch” + “git merge”
  • git clone
    Clone a copy of repository to your local folder
    git clone <url> <local folder>
    git clone –shallow : much more faster but no versions history