Basics of C Language – (01) Common Linux Commands and Tools

1. Terminal Related Operations

1. 1.

   Open the terminal on Ubuntu

   1. Click the Terminal icon

   2. Use the shortcut <span>ctrl+alt+t</span>

2. 2.

   Adjusting Font Size

   Increase:<span>ctrl shift +</span>

   Decrease:<span>ctrl -</span>

3. 3.

   Meaning of Command Line Prompt

   <span>linux@ubuntu:~$</span>

   linux: username (<span>whoami</span> command to get the username)

   ubuntu: hostname (<span>hostname</span> command to get the hostname)

   ~: path (<span>/home/linux/</span>)

   Regular user #root user

4. 4.

   User Switching

   <span>su username</span>

   eg:

   <span>su root</span>: Switch to root user

   <span>su linux</span>: Switch to linux user

1.2 ls Command

1.2.1 Function of ls Command

ls [OPTION]... [FILE]...

Function: Display files in the current directory on the terminal

1.2.2 Usage of ls Command

Everything in the Linux system is a file

<span>ls</span>: Display the contents of the current directory on the terminal

<span>ls -l</span>: Display file attributes along with the files

<span>ls -l README</span>: Display only the attribute information of the README file

<span>ls -lh</span>: Display file attributes with sizes converted to appropriate units

<span>ls -i</span>: Display inode numbers along with files (the unique identifier for files in the file system)

<span>ls -a</span>: Display all files including hidden files on the terminal (hidden files: files starting with a dot)

<span>ls -la .README</span>: Display the .README hidden file and its attribute information on the terminal

1.2.3 Detailed Explanation of Attributes Displayed by ls -l

drwxrwxr-x  2 linux linux 4096 8月  28 15:01 ARM_aaa

1. 1.

   File Types (7 types)

   bsp-lcd

   -: Regular file (white)

   d: Directory file (blue)

   c: Character device file (mouse /dev/input/mouse0, keyboard /dev/input/event0)

   b: Block device file (hard disk /dev/sda)

   l: Symbolic link file (similar to shortcuts in Windows)

   p: Pipe file (file for inter-process communication)

   s: Socket (file for data transmission over the network)

2. 2.

   File Permissions

   <span>rwx rwx r-x</span>

   User Group Other Users

   <span>r:</span>Readable permission 4

   <span>w:</span>Writable permission 2

   <span>x:</span>Executable permission 1

   <span>-:</span>No permission 0

   File permissions represented in octal: (octal prefix is 0)

   0775 rwxrwxr-x

   0664 rw-rw-r–

   0421 r—w—x

3. 3.

   Number of hard links or number of subdirectories

   2: Directory: represents the number of subdirectories

   2: File: represents the number of aliases (hard links)

4. 4.

   Username and Group Name

   <span>linux username linux group</span>

5. 5.

   File Size

   4096

6. 6.

   Timestamp

   August 28 15:01

7. 7.

   File Name

   ARM_aaa

1.3 cd Command

1.3.2 Function of cd Command

cd [directory]

Function: Change directory

cd relative_path
cd absolute_path

1.3.3 Usage of cd Command

<span>cd hello</span>: Enter the hello directory under the current directory

<span>cd ./hello</span>: Enter the hello directory under the current directory

<span>cd /home/linux/hello</span>: Use absolute path to enter the hello directory in the home directory

<span>cd /</span>: Enter the root directory

<span>cd ~ or cd /home/linux or cd</span>: Enter the /home/linux directory

<span>cd ..</span>: Enter the parent directory

<span>cd ../..</span>: Enter the grandparent directory

<span>cd -</span>: Enter the last directory you were in

Practice:

1. How to enter the etc directory under /home/linux?

Relative path:<span>cd ../../etc/</span>

Absolute path:<span>cd /etc</span>

2. Find the path of the mouse device file and check its attribute information?

cd /dev/input/
ls -l mouse0

3. Find the path of stdio.h and check its attribute information?

cd /usr/include/
ls -l stdio.h

4. Find the passwd file and check its attribute information?

cd /etc/
ls -l passwd

5. Find the path of the ls command and check its attribute information?

cd /bin/
ls -l ls

1.4 pwd Command

<span>pwd</span>: Command to display the current path

1.5 clear Command

<span>clear</span>: Command to clear the screen

Shortcut to clear the screen:<span>ctrl + l</span>

1.6 touch Command

1.6.1 Function of touch Command

touch  FILE...

Function: Create a regular file or update the file’s timestamp

1.6.2 Usage of touch Command

<span>touch 1.c</span>: If 1.c does not exist, create it; if it exists, update its timestamp

<span>touch 2.c 3.txt 4.doc</span>: Create files 2.c, 3.txt, and 4.doc if they do not exist

1.7 mkdir Command

1.7.1 Function of mkdir Command

mkdir [OPTION]... DIRECTORY...

Function: Create a directory

1.7.2 Usage of mkdir Command

<span>mkdir hello</span>: Create hello directory in the current directory

<span>mkdir duang heihei</span>: Create both duang and heihei directories at the same time

<span>mkdir -p 1/2/3</span>: Create directories with hierarchical relationships 1/2/3

<span>mkdir -m 0777 list</span>: Create list directory with permissions set to 0777

1.8 rm Command

1.8.1 Function of rm Command

rm [OPTION]... [FILE]...

Function: Delete files

1.8.2 Usage of rm Command

<span>rm 1.c</span>: Delete 1.c file

<span>rm 2.c 5.c</span>: Delete files 2.c and 5.c

<span>rm *.c</span>: Delete all files ending with .c

<span>rm -r hello/</span>: Delete directory

<span>rm -rf *</span>: Delete all files in the current directory ( -r: recursive, -f: force)

1.9 cp Command

1.9.1 Function of cp Command

cp [OPTION]... SOURCE... DIRECTORY

Function: Copy files

1.9.2 Usage of cp Command

<span>cp README ./list/</span>: Copy README file to the list directory in the current directory

<span>cp /usr/include/stdio.h .</span>: Copy stdio.h header file to the current directory

<span>cp -r ./list ./aaa</span>: Copy list directory to aaa directory

<span>cp README list/aa.c</span>: Copy README file to list directory and rename it to aa.c

Practice:

1. How to copy /etc/passwd and /etc/groff to /home/linux/hello?

cd ~
mkdir hello
cp /etc/passwd ~/hello
cp -r /etc/groff ~/hello

1.10 mv Command

1.10.1 Function of mv Command

mv  SOURCE... DIRECTORY

Function: Move or rename files

1.10.2 Usage of mv Command

<span>mv stdio.h ./list</span>: Move stdio.h file to ./list directory

<span>mv hello/ ./list</span>: Move hello directory to ./list directory (list exists)

<span>mv stdio.h www.h</span>: Rename stdio.h to www.h

<span>mv hello/ list/</span>: Rename hello directory to list directory (list does not exist)

1.11 cat Command

<span>cat FILE</span>: Display the contents of a file on the terminal

1.12 echo Command

<span>echo STRING</span>: Display a string on the terminal

<span>></span>: Redirect <span>echo helloworld > 1.c</span> Redirect the string helloworld to 1.c

<span>>></span>Append <span>echo helloworld >> 1.c</span> Append the string helloworld to 1.c

2. VIM Editor

2.1 Function of vim Editor

In the Linux system, you can use the vim tool to open a file and write your code in it.

2.2 Opening a File with vim Editor

vi filename

or

vim filename

2.3 Three Modes of vim

Command mode: Operations like copy, cut, paste, undo, etc.

Insert mode: Writing code

Bottom line mode: Operations like save, exit, etc.

2.4 Common Operations in the Three Modes of vim

Command mode

When opening a file, it defaults to command mode, or you can press the Esc key to return to command mode

<span>yy</span>: Copy 1 line

<span>4yy</span>: Copy 4 lines

<span>Copy any line</span>: Select the line you want to copy with the mouse, press the y key

<span>Copy from Ubuntu to Windows</span>: Hold down the shift key, select the line you want to copy with the mouse, right-click to copy, and paste in Windows.

<span>dd</span>: Cut 1 line

<span>4dd</span>: Cut 4 lines

<span>Cut any line</span>: Select the line you want to cut with the mouse, press the d key

<span>p</span>: Paste

<span>u</span>: Undo

<span>ctrl+r</span>: Cancel undo

<span>gg</span>: Jump to the first line of the file

<span>G</span>: Jump to the last line of the file

<span>gg=G</span>: Format and align code (align the entire text)

<span>Partial alignment</span>: Select the lines you want to align with the mouse, press the = key

<span>/STRING</span>: Search for a string (jump between found strings with n (next) or N (previous))

Insert mode

To enter insert mode from command mode:

<span>i</span>: Enter insert mode before the cursor

<span>I</span>: Enter insert mode at the beginning of the line where the cursor is

<span>a</span>: Enter insert mode after the cursor

<span>A</span>: Enter insert mode at the end of the line where the cursor is

<span>o</span>: Start a new line below the current line and enter insert mode

<span>O</span>: Start a new line above the current line and enter insert mode

Bottom line mode

To enter bottom line mode from command mode, press shift + :

<span>:q</span>: Exit

<span>:q!</span>: Exit without saving

<span>:w</span>: Save

<span>:wa</span>: Save all files

<span>:w filename</span>: Save as

<span>:wq or :x</span>: Save and exit

<span>:wqa</span>: Save and exit all files

<span>wq!</span>: Force save and exit

<span>:n</span>: Jump to line n (where n is a number)

<span>:sp filename</span>: Open multiple windows horizontally

<span>:vsp filename</span>: Open multiple windows vertically

<span>:set nonu</span>: Disable line numbers

<span>:set nu</span>: Enable line numbers

<span>:nohl</span>: Cancel highlight