Linux Basics

Basic commands

CD: switch to the current working directory.

jianghouren@jianghourendeMacBook-Pro ~ % cd test
jianghouren@jianghourendeMacBook-Pro test %
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Jump to the Downloads directory in the Test directory

jianghouren@jianghourendeMacBook-Pro test % cd ~/Downloads
jianghouren@jianghourendeMacBook-Pro Downloads % 

// CD ~ jumps to its own home directory. Equivalent to CD /Users/jianghouren.
// If the directory name is omitted, the directory is changed to the user's home directory.
jianghouren@jianghourendeMacBook-Pro test % cd ~   
jianghouren@jianghourendeMacBook-Pro ~ % pwd
/Users/jianghouren
jianghouren@jianghourendeMacBook-Pro ~ % cd test
jianghouren@jianghourendeMacBook-Pro test % cd /Users/jianghouren/Downloads
jianghouren@jianghourendeMacBook-Pro Downloads %
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PWD: View the location of the current directory.

jianghouren@jianghourendeMacBook-Pro test % pwd
/Users/jianghouren/test
jianghouren@jianghourendeMacBook-Pro test %
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Mkdir: creates a directory.

jianghouren@jianghourendeMacBook-Pro test % ls
  // Create directory 111
jianghouren@jianghourendeMacBook-Pro test % mkdir 111
jianghouren@jianghourendeMacBook-Pro test % ls
111
jianghouren@jianghourendeMacBook-Pro test %
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Create a multi-level directory

jianghouren@jianghourendeMacBook-Pro test % mkdir -p 1/2/3
jianghouren@jianghourendeMacBook-Pro test % ls
1
jianghouren@jianghourendeMacBook-Pro test % cd 1
jianghouren@jianghourendeMacBook-Pro 1 % cd 2
jianghouren@jianghourendeMacBook-Pro 2 % cd 3
jianghouren@jianghourendeMacBook-Pro 3 %
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cd .. Is to return the upper-level directory, and CD – is to return the working directory of the last operation.

jianghouren@jianghourendeMacBook-Pro test % ls
1
jianghouren@jianghourendeMacBook-Pro test % cd 1/2/3
  // Jump three levels above the current directory
jianghouren@jianghourendeMacBook-Pro 3% cd .. /.. /..// Go back to the directory of the last operation
jianghouren@jianghourendeMacBook-Pro test % cd -
~/test/1/2/3
jianghouren@jianghourendeMacBook-Pro 3 % cd -
~/test
jianghouren@jianghourendeMacBook-Pro test % cd -
~/test/1/2/3
jianghouren@jianghourendeMacBook-Pro 3 % cd ..
jianghouren@jianghourendeMacBook-Pro 2 % cd ..
jianghouren@jianghourendeMacBook-Pro 1 % cd ..
jianghouren@jianghourendeMacBook-Pro test %
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Ls: displays information in the current directory.

This can be viewed by ls-alt (where a is for all, L is for lists, and T is in reverse order).

jianghouren@jianghourendeMacBook-Pro test % ls
111	222
jianghouren@jianghourendeMacBook-Pro test % ls -a
.		..		.DS_Store	111		222
jianghouren@jianghourendeMacBook-Pro test % ls -al
total 16
drwxr-xr-x   5 jianghouren  staff   160  3 12 22:43 .
drwxr-xr-x+ 55 jianghouren  staff  1760  3 12 22:22. -rw-r--r--@1 jianghouren  staff  6148  3 12 11:48 .DS_Store
drwxr-xr-x   4 jianghouren  staff   128  3 12 22:13 111
drwxr-xr-x   2 jianghouren  staff    64  3 12 22:43 222
jianghouren@jianghourendeMacBook-Pro test % ls -alt
total 16
drwxr-xr-x   5 jianghouren  staff   160  3 12 22:43 .
drwxr-xr-x   2 jianghouren  staff    64  3 12 22:43 222
drwxr-xr-x+ 55 jianghouren  staff  1760  3 12 22:22. drwxr-xr-x4 jianghouren  staff   128  3 12 22:13 111
-rw-r--r--@  1 jianghouren  staff  6148  3 12 11:48 .DS_Store
jianghouren@jianghourendeMacBook-Pro test %
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Code block:. Represents the current directory,.. Indicates the parent directory.

jianghouren@jianghourendeMacBook-Pro test % cd .
jianghouren@jianghourendeMacBook-Pro test % ls -alt
total 16
drwxr-xr-x   4 jianghouren  staff   128  3 12 11:48 .
drwxr-xr-x   2 jianghouren  staff    64  3 12 11:48 111
-rw-r--r--@  1 jianghouren  staff  6148  3 12 11:48 .DS_Store
drwxr-xr-x+ 55 jianghouren  staff  1760  3 12 11:44. jianghouren@jianghourendeMacBook-Pro test % cd .. jianghouren@jianghourendeMacBook-Pro ~ %Copy the code

Code block: drwxr-xr-x, d for directory, rwxr-xr-x for permission.

jianghouren@jianghourendeMacBook-Pro test % cd 111
jianghouren@jianghourendeMacBook-Pro 111 % ls
	// Create a new file and write the contents.
jianghouren@jianghourendeMacBook-Pro 111 % echo "123456" >> 1.txt
jianghouren@jianghourendeMacBook-Pro 111 % ls
1.txt
jianghouren@jianghourendeMacBook-Pro 111 % ls -alt
total 8
  // - This is a normal file.
-rw-r--r--  1 jianghouren  staff    7  3 12 18:24 1.txt
drwxr-xr-x  3 jianghouren  staff   96  3 12 18:24 .
drwxr-xr-x  4 jianghouren  staff  128  3 12 11:48. jianghouren@jianghourendeMacBook-Pro111 %
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Cp: short for copy, copy files.

jianghouren@jianghourendeMacBook-Pro test % echo "aaaa" >> 5.txt
jianghouren@jianghourendeMacBook-Pro test % ls
5.txt
jianghouren@jianghourendeMacBook-Pro test % cp 5.txt 1.txt
jianghouren@jianghourendeMacBook-Pro test % ls
1.txt	5.txt
jianghouren@jianghourendeMacBook-Pro test %
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Copy the 1. TXT file in directory 111 of the current subdirectory to the current directory.

jianghouren@jianghourendeMacBook-Pro test % cp ./111/1.txt .
jianghouren@jianghourendeMacBook-Pro test % ls
1.txt	111
jianghouren@jianghourendeMacBook-Pro test % ls ./111
1.txt
jianghouren@jianghourendeMacBook-Pro test %
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Cat: View the file content.

jianghouren@jianghourendeMacBook-Pro test % cat 1.txt
123456
jianghouren@jianghourendeMacBook-Pro test %
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Rm: Deletes a file or directory.

jianghouren@jianghourendeMacBook-Pro test % ls
1.txt	111
  // Delete files.
jianghouren@jianghourendeMacBook-Pro test % rm 1.txt
jianghouren@jianghourendeMacBook-Pro test % ls
111
  // You cannot delete directories in this way.
jianghouren@jianghourendeMacBook-Pro test % rm 111
rm: 111: is a directory
  // Delete the directory. R for loop, f for force.
jianghouren@jianghourendeMacBook-Pro test % rm -rf 111
jianghouren@jianghourendeMacBook-Pro test % ls
jianghouren@jianghourendeMacBook-Pro test %
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Sudo: Switch the current user’s permissions, for example, to root.

jianghouren@jianghourendeMacBook-Pro test % id
uid=501(jianghouren) ......
  // Create a directory using root.
jianghouren@jianghourendeMacBook-Pro test % sudo mkdir 222
Password:
jianghouren@jianghourendeMacBook-Pro test % ls
222
jianghouren@jianghourendeMacBook-Pro test % ls -alt
total 16
drwxr-xr-x   4 jianghouren  staff   128  3 12 19:00 .
  // As you can see, the creator here is root.
drwxr-xr-x   2 root         staff    64  3 12 19:00 222
-rw-r--r--@  1 jianghouren  staff  6148  3 12 11:48 .DS_Store
drwxr-xr-x+ 55 jianghouren  staff  1760  3 12 11:44.// Create directories with normal permissions.
jianghouren@jianghourendeMacBook-Pro test % mkdir 111
jianghouren@jianghourendeMacBook-Pro test % ls -alt
total 16
drwxr-xr-x   5 jianghouren  staff   160  3 12 19:00 .
  // You can see that the creators of directories 111 and 222 are different.
drwxr-xr-x   2 jianghouren  staff    64  3 12 19:00 111
drwxr-xr-x   2 root         staff    64  3 12 19:00 222
-rw-r--r--@  1 jianghouren  staff  6148  3 12 11:48 .DS_Store
drwxr-xr-x+ 55 jianghouren  staff  1760  3 12 11:44. jianghouren@jianghourendeMacBook-Pro test %Copy the code

Now you can delete the JIANGhouren directory with normal permissions. The jianghouren directory is a subdirectory of test and is created by jianghouren.

jianghouren@jianghourendeMacBook-Pro test % ls
111	222
jianghouren@jianghourendeMacBook-Pro test % rm -rf 222
jianghouren@jianghourendeMacBook-Pro test % ls
111
jianghouren@jianghourendeMacBook-Pro test %
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However, the JIANGhouren user has the permission to create and delete the jianghouren directory. The jianghouren user has the permission to create and delete the jianghouren directory.

jianghouren@jianghourendeMacBook-Pro test % cd 222
jianghouren@jianghourendeMacBook-Pro 222 % sudo mkdir 333
jianghouren@jianghourendeMacBook-Pro 222 % ls
333
jianghouren@jianghourendeMacBook-Pro 222 % mkdir 444
mkdir: 444: Permission denied
jianghouren@jianghourendeMacBook-Pro 222 % rm -rf 333
rm: 333: Permission denied
jianghouren@jianghourendeMacBook-Pro 222 % ls
333
jianghouren@jianghourendeMacBook-Pro 222 % sudo rm -rf 333
jianghouren@jianghourendeMacBook-Pro 222 % ls
jianghouren@jianghourendeMacBook-Pro 222 %
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Others: On Mac, Control + L clears the screen.

Installation tools

Apt: Ubuntu

The brew: Mac

Yum: Centos

Basic Vim operations

Basic commands:

  • Vim 1.txt –> Create the file (if it does not exist) and enter edit mode

  • :w –> Save the file

  • :q –> Exit the file

  • :wq –> Save the configuration and exit

  • I –> Edit mode

  • H left, L right, K up, J Down –> cursor movement (exit edit mode)

  • Yy copy, P paste, DD delete. (Exit editing mode)

  • Press Esc to exit edit mode

Linux vi/vim

Environment variables in Linux

Environment variables:

Three important environment variables:

  • PATH (command executed).

For example, the ls command actually looks in the PATH environment variable

jianghouren@jianghourendeMacBook-Pro ~ % which ls
/bin/ls
jianghouren@jianghourendeMacBook-Pro ~ %
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  • PKG_CONFIG_PATH (PKg-config).

    Use the library file with the pkg-config + argument. The library files to use are also found in PKG_CONFIG_PATH.

    The pkg-config command is used when C/C++ applications are developed and libraries are linked.

  • LD_LIBRARY_PATH.

Changes to environment variables:

In Windows, add at the end by setting environment variables.

For Linux:

~/.bashrc (setting environment variables for.bashrc files in the current user’s working directory)

On Mac:

Through the env to view environment variables, through env | grep PATH to check the PATH.

Edit via vim ~/.bash_profile (~/.bash_profile sets environment variables in the.bash_profile file in the current user’s working directory)

After the Settings are complete, run source ~/.bash_profile to take effect.

note

References:

Moocs – Audio and Video Basics (Li Chao)

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