codecademy-command line

codecademy-command line_filesystem

$:shell prompt (命令提示符)

In the terminal, first you see $. This is called a shell prompt. It appears when the terminal is ready to accept a command.
When you type ls, the command line looks at the folder you are in, and then "lists" the files and folders inside it. The directories 2014, 2015, and the file hardware.txt are the contents of the current directory
```
$ pwd
/home/ccuser/workspace/blog
```
pwd stands for "print working directory". It outputs the name of the directory you are currently in, called theworking directory.

Here the working directory is blog/. In Codecademy courses, your working directory is usually inside thehome/ccuser/workspace/ directory.

Together with ls, the pwd command is useful to show where you are in the filesystem.
```
$ cd 2015
```
1. cd stands for "change directory". Just as you would click on a folder in Windows Explorer or Finder, cdswitches you into the directory you specify. In other words, cd changes the working directory.
2. The directory we change into is 2015. When a file, directory or program is passed into a command, it is called an argument. Here the 2015 directory is an argument for the cd comman
```
$ cd jan/memory
```
  To navigate directly to a directory, use cd with the directory's path as an argument. Here, cd jan/memory/command navigates directly to the jan/memorydirectory.
```
$ cd ..
```
  To move up one directory, use cd ... Here, cd ..navigates up from jan/memory/ to jan/.
3. ```
$ mkdir media
```
  The mkdir command stands for "make directory". It takes in a directory name as an argument, and then creates a new directory in the current working directory.
  
  Here we used mkdir to create a new directory namedmedia/ inside the feb/ directory.
4. ```
touch keyboard.txt
```
  The touch command creates a new file inside the working directory. It takes in a filename as an argument, and then creates an empty file in the current working directory.
  
  Here we used touch to create a new file namedkeyboard.txt inside the 2014/dec/ directory.
5. Congratulations! You've learned five commands commonly used to navigate the filesystem from the command line. What can we generalize so far?
  - The command line is a text interface for the computer's operating system. To access the command line, we use the terminal.
  - A filesystem organizes a computer's files and directories into a tree structure. It starts with theroot directory. Each parent directory can contain more child directories and files.
  - From the command line, you can navigate through files and folders on your computer:
    - pwd outputs the name of the current working directory.
    - ls lists all files and directories in the working directory.
    - cd switches you into the directory you specify.
    - mkdir creates a new directory in the working directory.
    - touch creates a new file inside the working directory.
    - ```
    $ ls -a
    .  ..  .preferences  action  drama comedy  genres.xt
```
  1. The ls command lists all files and directories in the working directory.
  2. The -a modifies the behavior of the ls command to also list the files and directories starting with a dot (.). Files started with a dot are hidden, and don't appear when using ls alone.
  The -a is called an option. Options modify the behavior of commands. Here we used ls -a to display the contents of the working directory in more detail.
  
  In addition to -a, the ls command has several more options. Here are three common options:
  - -a - lists all contents, including hidden files and directories
  - -l - lists all contents of a directory in long format
  - -t - order files and directories by the time they were last modified.
  - $ ls -l drwxr-xr-x 5 cc eng 4096 Jun 24 16:51 action drwxr-xr-x 4 cc eng 4096 Jun 24 16:51 comedy drwxr-xr-x 6 cc eng 4096 Jun 24 16:51 drama -rw-r--r-- 1 cc eng 0 Jun 24 16:51 genres.txt
    
    The -l option lists files and directories as a table. Here there are four rows, with seven columns separated by spaces. Here's what each column means:
    
    Access rights. These are actions that are permitted on a file or directory.
    
    Number of hard links. This number counts the number of child directories and files. This number includes the parent directory link (..) and current directory link (.).
    
    The username of the file's owner. Here the username is cc.
    
    The name of the group that owns the file. Here the group name is eng.
    
    The size of the file in bytes.
    
    The date & time that the file was last modified.
    
    The name of the file or directory.
    
    $ ls -alt drwxr-xr-x 4 cc eng 4096 Jun 29 12:22 . -rw-r--r-- 1 cc eng 0 Jun 29 12:22 .gitignore drwxr-xr-x 5 cc eng 4096 Jun 30 14:20 .. drwxr-xr-x 2 cc eng 4096 Jun 29 12:22 satire drwxr-xr-x 2 cc eng 4096 Jun 29 12:22 slapstick -rw-r--r-- 1 cc eng 14 Jun 29 12:22 the-office.txt
    
    The -t option orders files and directories by the time they were last modified.
    
    In addition to using each option separately, like ls -aor ls -l, multiple options can be used together, likels -alt.
    
    Here, ls -alt lists all contents, including hidden files and directories, in long format, ordered by the date and time they were last modified.
    
    cp frida.txt lincoln.txt
    
    The cp command copies files or directories. Here, we copy the contents of frida.txt into lincoln.txt.
    
    cp biopic/cleopatra.txt historical/
    
    To copy a file into a directory, use cp with the source file as the first argument and the destination directory as the second argument. Here, we copy the filebiopic/cleopatra.txt and place it in the historical/directory.
    
    cp biopic/ray.txt biopic/notorious.txt historical/
    
    To copy multiple files into a directory, use cp with a list of source files as the first arguments, and the destination directory as the last argument. Here, we copy the files biopic/ray.txt and biopic/notorious.txtinto the historical/ directory.
    
    cp * satire/
    
    In addition to using filenames as arguments, we can use special characters like * to select groups of files. These special characters are called wildcards. The * selects all files in the working directory, so here we use cp to copy all files into the satire/ directory.
    
    cp m*.txt scifi/
    
    Here, m*.txt selects all files in the working directory starting with "m" and ending with ".txt", and copies them to scifi/.
    
    The mv command moves files. It's similar to cp in its usage.
    
    mv superman.txt superhero/
    
    To move a file into a directory, use mv with the source file as the first argument and the destination directory as the second argument. Here we move superman.txtinto superhero/.
    
    mv wonderwoman.txt batman.txt superhero/
    
    To move multiple files into a directory, use mv with a list of source files as the first arguments, and the destination directory as the last argument. Here, we move wonderwoman.txt and batman.txt intosuperhero/.
    
    mv batman.txt spiderman.txt
    
    rm waterboy.txt
    
    The rm command deletes files and directories. Here we remove the file waterboy.txt from the filesystem.
    
    rm -r comedy
    
    The -r is an option that modifies the behavior of therm command. The -r stands for "recursive," and it's used to delete a directory and all of its child directories.
    
    Be careful when you use rm! It deletes files and directories permanently. There isn't an undelete command, so once you delete a file or directory withrm, it's gone.
    
    Congratulations! You learned how to use the command line to view and manipulate the filesystem. What can we generalize so far?
    
    Options modify the behavior of commands:
    
    ls -a lists all contents of a directory, including hidden files and directories
    
    ls -l lists all contents in long format
    
    ls -t orders files and directories by the time they were last modified
    
    Multiple options can be used together, likels -alt
    
    From the command line, you can also copy, move, and remove files and directories:
    
    cp copies files
    
    mv moves and renames files
    
    rm removes files
    
    rm -r removes directories
    
    Wildcards are useful for selecting groups of files and directories