linux fundamentals from scratch…

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1. Opening and Closing the Terminal

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open : Ctrl+alt+t close: Ctrl+d

2. Basic Commands

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echo : returns command line arguments to standard output. date : show the current date and time cal : show the calendar cat : read and write files cut : divided into blocks and gives u fields grep : grep the content from the file cd : change directories ls : list files and directories man : man command is use for finding man pages. apropos: to finding man pages or commands.

3. Command History

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history !! : to run previous command !n : to run command from history using index number

4. Some Important Definitions

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command : an instruction typed in the terminal and submitted to the shell for interpretation and a command must be a valid program on shell’s path.e.g. cal , cat etc shell : a program that interprets commands for meaning (arthaart). terminal : a graphical window where command can be typed and submitted to the shell

5. Command Structure

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command_Name -option(--option) argumentscommand

5.1 Command name :- command_Name must be a valid program on shell’s path. to check the which command is it. 5.2 Options : - to customize the commands behavior 5.2.1 Short-form Options : -option 5.2.2 Long-form Options : - -option 5.2.3 Command Line Arguments : args 5.2.4 Arguments for Options : command line arguments are type of input that commands

operate on e.g. `cal` 12 2019, `echo` "hello"

6. Using the Manual

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man k “search” it is help to search the programs in systems and it provide the whole info about the command

7. find

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This use search files and directories in system by there name, size, permission and you also execute commands in it. this is not as much fast compare to locate command. this work as ls command works but recursively.

find [options]… …

8. Command Input and Output

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Standard Data Streams can be redirected and are identified using their stream number.

8.1 Redirecting Standard Output: 1> or > destination 8.2 Redirecting Standard Error: 2> destination 8.3 Redirecting Standard Input: 0< or < destination 9. Piping : Redirection of the standard output of one command to the standard input of another command is known as piping. it is represented by pip symbol (|) e.g. commandOne –options arguments | commandTwo –options arguments

9 Taking “Snapshots” of pipeline data using the tee command

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Redirecting during a pipeline breaks the pipeline.For example, this wouldn’t work: commandOne –options arguments > snapshot.txt | commandTwo –options arguments Because redirection is processed by the shell before piping is, snapshot.txt would be created,but this locks up the standard output stream and therefore no data can be passed through the pipeline to commandTwo. NB: Redirection breaks pipelines However, the tee command allows us to take a “snapshot” of the data in the pipeline without breaking the pipeline. commandOne –options arguments | tee snapshot.txt | commandTwo –options arguments Here, a snapshot of the data coming out of commandOne is saved in snapshot.txt, but the data is also successfully piped through to commandTwo.

e.g. date | tee /home/user/date.txt | cut -d " " -f 1 > /home/user/today.txt

Piping to commands that only accept command line arguments by using xargs

Piping connects the standard output of one command to the standard input of another command. But what if the second command doesn’t accept standard input? e.g. the echo command. The key is to transform the data coming in, into command line arguments. This is possible using the xargs command. For example, this would not work: commandOne –options arguments | echo This would work: commandOne –options arguments | xargs echo

e.g. date | tee /home/user/date.txt | cut -d " " -f 1 | tee /home/user/today.txt | xargs echo "today is "

10. Aliases :

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Aliases allow you to save your pipelines and commands with easy to remember nicknames so that they can be used later much easier.

You define aliases in your .bash_aliases file in your home directory. if you don’t have it in your home directory so should make it.

Here is how you define an alias in .bash_aliases: alias aliasName=”THING YOU WANT TO ALIAS”

e.g. alias mojkrdi=‘date | tee /home/user/date.txt | cut -d " " -f 1 | tee /home/user/today.txt | xargs echo "today is "’

11. file system

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/       : The Very Top (Root) of The File Tree. Holds Everything else.

/bin    : Stores Common Linux user command binaries. e.g date, cat, cal commands 
	  are in here.

/boot   : Bootable linux Kernel and bootloader config files

/dev    : Files representing devices. tty=terminal, fd=floppydisk, 
          (sd or hd) = harddiss, ram=RAM, cd=CD-ROM

/etc    : Administrative Configuration files. The format for many of these 
	  configuration can be found in section 5 of the Linux Manual.

/home   : Where the home directories for regular users are stored. For example, 
	  mine is at /home/kali

/media  : Unlike /dev, /media is usually where removable media (USB sticks, 
	  external hard drives etc.) are mounted.

/lib     : Contains shared libraries needed by applications in /bin and /sbin to 
	   boot the system.

/mnt    : A place to mount external devices. This can still be used but has been 
          superseded by /media

/misc   : A directory used to sometimes automount filesystems on request.

/opt    : Directory Structure used to store additional (i.e optional) software

/proc   : Information about System Resources

/root   : The home folder for the root user aka the superuser (similar to the 
          administrator on Windows)

/sbin   : Contains administrative commands (binaries) for the root (super) user.

/tmp    : Contains temporary files used by running applications.

/usr    : Contains files pertaining to users that in theory don’t change after 
          installation.

/var    : Contains directories of variable data that could be used by various 
          applications. System log files are usually found here.

12. rules & convention of naming files and folder in Linux

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1. All files name are case sensitive
2. You can use upper and lowercase letters, numbers, “.” (dot), and “_” (underscore) symbols and blank spaces but avoid to use blank spaces in linux because it will create huge mess when you working at command line interface. yeah its a nightmare in linux don’t do that.
3. No need you extension in file name but it is good to keep it to make understand which file is this

13. Use of template directory

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whatever file we make in template directory. will get it as template to reuse it.

14. Navigation file system all

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• use pwd command to see where are you.

• use ls command to find or see subdirectories and files in directory.

  ls has own flags which helps us a lot like -a to see hidden stuff, -l to see info in list form and all the info about files and folders and -h for human readable

• use cd command to change directories.

15. Kinds of paths in linux

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Absolute paths starts at the base (/) directory.

e.g. /home/user/Desktop this is absolute path

Relative paths starts from the current directory.

Suppose you are in user and wanna go in Desktop directory so rather then you type cd /home/user/Desktop instead you can just type cd Desktop. it will work fine because now it use relative path which starts from current directory.

16. Wildcard

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A wild card is a character that can be used as a substitute for any of class of character in search, thereby greatly increasing the flexibility and efficiency of searches.

we have mainly three types of wildcard

1. * astric can be use as a character or as a string. This is useful when searching for documents or files but only remembering a part of its name.
2. ? question mark is use for only one character. This is useful when you have a list of similarly named files and unsure of a few characters.
3. [] is used to match any occurrences of characters defined inside the brackets.

17. Creating files and Directories

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• use touch command use create a empty file

  e.g. touch *fileNam*

• use echo to redirect content in a file and its also create that file

  e.g. echo "my file content and it also create the new file" > *fileName*

  if _fileNam_e file is already exist then it will rewrite it after deleting all content in fileName file

• use mkdir to create a folder or directory also mkdir stands for make directory

  e.g. mkdir *folderName* and mkdir -p /folderName/insideAFolder/againAFolder flag -p create all these folder in a one command

• creating files and folder with the help of brace expansion {}

  suppose you are working on project and use need create folder according to month name for 5 year and each and every folder have 30 files withing them. so how would you do it, we can do it in just one command yeah that’s linux has incredible power. so lets use it -

  mkdir {Jan,Feb,Mar,Apr,May,Jun,Jul,Agu,Sep,Oct,Nov,Dec}_{2020,2021,2022,2023,2024}

  this command create 60 folder there name will be like

  Jan_2020

  Jan_2021

  jan_2022

  jan_2023

  jan_2024

  Feb_2020

  and so on

  we have also short cut for that-

  mkdir {Jan,Feb,Mar,Apr,May,Jun,Jul,Agu,Sep,Oct,Nov,Dec}_{2020..2024}

  this two .. will work for any kind of sequence like {A..Z} , {a..b} , {1..100}

  Now going to create files withing them

  touch {Jan,Feb,Mar,Apr,May,Jun,Jul,Agu,Sep,Oct,Nov,Dec}_{2020..2024}/file{1..30}

18. Removing files and folders

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rm fileName this will simply remove fileName file

rm -r FolderName this will delete that folder and all the files in this folder -r stands for recursively so that’s by is delete all the things recursively whatever inside the folder it too dangers command there is no to retrieve all those files and folders, for making it safe next command will help you

rm -ri FolderName there is -i stands for interactively. before deleting any file and folder it will ask you can i delete this you type y for allow and n for denial

rm file* there we are using * for deleting all files in current directory which matches this file* pattern.

rm *[1,2]* it will work like above one.

19. Coping files and folders

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cp originalFile copiedfile copy file content into another file.

cp fileName... <destination\\> copy files to another place.

cp -r folder <destination> copy folder to another directory.

20. Renaming and moving files and folders

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mv oldName newName renaming of file.

mv fileName... <destination\\> move file to somewhere else.

mv -i fileName... <destination> move file safely in another directory, where same name file is exist.

mv folder <destination> move folder to another folder.

mv folder <destination>/changeNameOfFolder moving the folder and change its name at the same time.

21. Change permissions of a file

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• chown change owner and group of a file

  e.g. chown user:group file

• chmod change file permissions of a file

  • 1 execute
  • 2 written
  • 3 execute and written
  • 4 read
  • 5 execute and read
  • 6 written and read
  • 7 read, write and execute

  e.g. chmod 777 file

  first 7 for user, second for group and third for everyone else.

22. locate

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The locate command is the quickest and simplest way to search for files and directories by their names. it is return the full path of file for that its use the databasedb.

locate [option] …

The locate command also accepts patterns containing globbing characters such as the wildcard character *.

23. operator

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In linux we very powerful operators like

1. &&,
2. &,

3. , »,

4. <, «,
5. |,
6. $,
7. ; .

24. liking

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25. viewing files :

26. sorting data :

27. searching file content :

28. file archive and compression :