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DAY 3.md

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DAY3

Notes ~ :

  1. OS version of system is stored in /etc/os-release
  2. [Command] - - > [SHELL] - - >(checks) - - > [PATH] - - > (interpretes) - - > [Kernel] - - > [ HDD ]
  3. Upon completion of all processes an exit code is created which defines that the command or program completed successfully ( if successfull - > exit code == 0 and if not successfull - > exit code != 0 )
  4. Python uses 'sh' shell for interpretation
  5. 'grep' stands for General Regular Expression
  6. Pipeline ( Pipe ) - - > Symbol '|' - - > Syntax { command1 | command2) - - > output of command1 is input to command2
  7. SCM - > Source Code Management - > differentiate programs with respect to code
  8. VCS - > Version Control System - > differentiate programs with respect to their versions
  9. Technologies using SCM are ~ : * SVN * Git / GITHUB { Git works on system level && GITHUB works on server side } * Bit Bucket
  10. what is cloning?- > downloading a repository from github
  11. Archive - > an unordered collection of data(files in a folder) - > no effect on size
  12. Compression - > an ordered/compact collection of data - > size reduces

LINUX Commands ~ :

  • $ echo $PATH # gives the path of various directories where primitive commands are stored (Director1 : Directory2 : DirectoryN)
  • $ wc -l file-name.extension # count no. of line in file
  • $ wc -w file-name.extension # count no. of words in file
  • $ wc -c file-name.extension # count no. of characters in file
  • $ grep search-text where-to-search # finds the text with similar pattern
  • $ grep -i search-text where-to-search # finds the text (Non-Case Sensitive)
  • $ grep -w search-text where-to-search # find the text with exact word
  • $ grep -v search-text where-to-search # find the text that doesn't match the search-text
  • $ head -n file-name # extracts n lines from top of file
  • $ tail -n file-name # extracts n lines from bottom of file
  • $ commandfile-name.txt # back quotes make command work if no space is given
  • $ tar -cvf new-file.tar file-name.extension # c - create ; v - visual ; f - forcefully , creates a archive
  • $ ls -lh # shows file size in respective formats (kb/mb/gb)
  • $ ls -l # shows file info ( size, permissions, name) , size in kb
  • $ tar -tvf new-file.tar file-name.extension # shows the files present in archive
  • $ tar -xvf new-file.tar # extracts all files out of tar/archive
  • $ tar -czvf new.tar.gz file1.ext file2.ext # z- gzip , it commpreses the large files into size of Kbs

Make your own Command ~ :

write your code and save it in /usr/bin example - - : vim /usr/bin/pykid

Input/Output Redirection ~ :

Output Redirection ~ :

Redirection the output of a task/command to - - >
 * File         * E-Mail          * Another System
 * RAM          * Printer         * Whatsapp

File Redirection ~ :

  * $ command > file-name.extension       # overwrite, stores output of command in file
  * $ command >> file-name.extension      # append data, stores output of command in file
  * $ command 2> file-name.extension      # overwrite, stores output(error command) if an incorrect command is written
  * $ command 2>> file-name.extension     # append data, stores output(error command) if an incorrect command is written
      ('2>' it will run the command and show output on terminal if command is correct and nothing will be saved in file )
  * $ command &> file-name.extension      # sends the output of command either command is correct or not

RAM Redirection ~ :

  * Based on Pipeline

E-mail Redirection ~ :

  * $ mail -s 'subject-for-mail' mail-id-of-receiver
    Conditions for mail to be sent through this method are ~ :
      1. Need a Public IP  - - > its a unique and purchased IP taken from ISP
      2. IP should be white-listed - - > any IP which visits porn sites or non-certified,dangerous sites is made non-white-              listed

System to System Redirection ~ :

  1. type the following command in receiver system            # Host System
    $ nc -l xxxx                  # nc stand for network connector and xxxx can have value from 0000 to 9999
  2. type the following command in sender system              # Sub Systems
    $ nc IP-of-Host-System xxxx   # xxxx have value set by host-system

Important Python Modules ~ :

  1. Commands -- > used only in Python 2
  2. os
  3. webbrowser
  4. subprocess

TASKS

  1. Run application from terminal but it should not run from icon(GUI) { alter the name of code-file in /usr/bin (firefox to firefoxs) and set alias in bashrc for firefox to firefoxs (alias firefox='firefoxs') }
  2. How to Write Hello World in a Directory. { impossible, as a directory has no storage/memory of itself }
  3. Read about RAM { main memory,temporary, 2 types - SRAM nd DRAM, only data being used is stored }
  4. Find no. of lines in a file { file-handling in python, code saved in repo }
  5. Count no. of lines in a file without saving the file { input in terminal is saved in RAM, done, code i repo }
  6. open a browser-tab using python, find top 5 URLs and store them in list then open those 5 URLs and store top 5 in list again
  7. Redirect message from terminal to whatsapp