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Introduction to Linux.Rpres
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Introduction to Linux.Rpres
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Introduction to Linux
========================================================
author: Ouso D. O.
date: 09-08-2018
autosize: true
# Sensei penguin!
========================================================
Objectives
========================================================
- Understand basic Linux terminologies
- Reasons to adopt Linux
- Understand basic Linux filesystem
- Differentiate between relative and absolute paths
- Learn to make dirs and common operations with directories
- Be able to explain the "ls" output
- Know how to manipulate files and file contents
- Basics of shell scripting
Basic Terminologies
========================================================
- **Kernel** - the core functionality of an operating system, translates commands from other
software directly to the hardware interfaces.
- **Distributions** - operating systems based on the Linux kernel, eg. Ubuntu (Deb), CentOS (Fedora) & openSUSE (SUSE)
- **CLI/Terminal** - a method of interaction with the computer based on text commands entered at the prompt
- **GUI** - a method of interaction with the computer that makes use of visual representations of elements
Why Linux?
========================================================
- It is FLOSS-based
- World's largest and most prevalent open source
- Long Term Support (LTS)
- Many developers around the world contribute to it
- Most secure
- Customizable
- Multi-user, multi-tasking (servers)
- A Major force in computing, eg. supercomputers, phones, stock exchanges etc
File System
========================================================
- Partition - a logical part of a disk
- Filesystem - a method of storing/finding files on a hard disk
Linux uses **'/'** to separate paths, windows uses **'\'**.
_Below is the partial Linux FS representation_
Linux
=====================================
A comparison between Win and Linux filesystems is illustrated in the image below
- For more details see the Linux [Filesysytem Hierarchy Standard](https://refspecs.linuxfoundation.org/FHS_3.0/fhs-3.0.pdf)
- A new terminal will land you in the home directory
- While on the terminal you will be associated to one directory at a time called working dir/current dir
Paths
========================================================
- The command **_pwd_** (present working directory) returns the absolute path to your working dir
Two types of paths exist:
- Absolute path - describe the path of a file/dir from the root (/) all the way to it
- Relative path - describe the path to a file/dir from the current working dir
Let's illustrate the two paths with a fig
=================================================
What is the absolute path to "**README.md**"? **_/home/oface/Git/Images/README.md_**
What is the path to "**LinuxFS.png**" assuming my current working directory is PythonCoding? **_./../Images/LinuxFS.png_**
Directories and associated commands
========================================================
- In Linux "__Directories__" are equivalent to Windows "__Folders__"
Some of the commands associated with directories include:
- To create a dir use **_mkdir_** <_dirName_>
- To remove a dir use **_rmdir_** <_dirNmae_>
- To move from one dir to another, use **_cd_** <_dirPath_>
- To list dir content, use **_ls_** while inside the dir or **_ls_** <_dirPath_> from a different dir
- To rename a dir, use **_mv_** <_oldName_> <_newName_>
Output of the ls -lh Cmd
========================================================
<ol type="I">
<li>File(-) or Directory(d) or Symlink(l)</li>
<li>Owner file permissions</li>
<li>Group file permissions</li>
<li>Global user file permissions</li>
<li>Number of links</li>
<li>Owner name</li>
<li>Owner group</li>
<li>File size</li>
<li>Date and time of last modification</li>
<li>File/Directory name</li>
</ol>
"__total BLOCKS__" means the total disk allocations of the dir content listed
Some shortcuts
========================================================
- **_cd~_** or **_cd_**: takes you to home dir from wherever
- **_cd -_**: takes you to previous dir
- **_cd .._**: takes you to parent dir
- **_Ctrl+L_**: clears terminal
- **_Ctrl+C_**: cancels a running program
- **_Crtl+D_**: exit terminal
- **_Tab_**: auto complete
- **_Tab Tab_**: display possibities for autocomplete
Manipulating files
========================================================
- **_touch_**: to create, modify and change timestamp of a file; syntax **_touch_** <_fileName_>
- **_gedit_**: to create a text file; syntax **_gedit_** <_fileName_>
- **_wget_**: is a free utility for non-interactive download of files from the Web. It supports HTTP, HTTPS, and FTP protocols, as well as retrieval through HTTP proxies; syntax **_wget_** <_option(s)_> <_URL_>
- **_cp_**: copy file/dir; syntax **_cp_** <_origiLocation_> <_finalLocation_>
- **_rm_**: delete files; syntax **_rm_** <_file_>
- **_mv_**: move file/dir; syntax **_mv_** <_origiLocation_> <_finalLocation_>
To figure out the many possible options of a command use **_man_** <_command_> to get a summary manual of how to use that command. Linux commands generally follow the syntax **_command_** <_option(s)_> <_argument(s)_>
Accessing file contents
========================================================
- **_cat_**: to view content of a small file in stdout; syntax **_cat_** <_file_>
- **_more_**: to view a large file in stdout by scrolling unilaterally - downwards; syntax **_more_** <_file_>. Use keyboard "__Spacebar__" to scroll page by page
- **_less_**: to view a large file in stdout by scrolling bilaterally - up/downwards; syntax **_more_** <_file_>. Use keyboard "__Spacebar__" to scroll page by page
- **_head_**: explore, by default, ten top lines of a file: syntax **_head_** <_file_>
- **_tail_**: explore, by default, ten last lines of a file: syntax **_tail_** <_file_>
- **_wc_**: word count, to explore number of lines, words and characters of a file: syntax **_wc_** <_file_>
Manipulating file contents
========================================================
- **_sort_**: re-order file content alphabeti/numeri-cally; syntax **_sort_** <_file_>
- **_uniq_**: remove redundancies; syntax **_uniq_** <_file_>
- **_join_**: compare content; syntax **_join_** <_file1_> <_file2_>. Output common entries
- **_diff_**: compare content; syntax **_diff_** <_file1_> <_file2_>. Output the differences
- **_grep_**: **G**lobal **R**egular **E**xpression **P**attern, search for patterns; syntax **_grep_** <_pattern_> <_file_>
__Wildcards__: special characters used as patterns to help with quick targeting of files or file sections/dirs, see [document](https://bioinf.comav.upv.es/courses/linux/_downloads/fsf_cmd_manual.pdf) on wildcards starting from page 23
Shell scripting
========================================================
__What is a script?__
A short program written in the programming languages used for automation, especially when handling huge amounts of data which require similar treatment. A shell script file basically contains a set of instructions in a shell language to be performed on files
__What is shebang?__
Begins a shell script, to set the interpreter environment to be used to execute the set of instructions that follow, "_bash_" is such an interpreter, several others exist. Syntax **__#!AbsolutePathOfInterpreter__** eg. **__#!/bin/bash__** or **__#!/usr/bin/python__**
After writing your script you will need to make it executable by using the **_chmod_** command before you can run it
# Let's try out a short script that prints out a sentence. . .
========================================================
**Thank You**
email: [email protected]
twitter: @ousodanos