Bash Scripting - making your life easier

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We do tedious repetitive tasks all the time

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But there is a solution!

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Bash.

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Bash scripting – making your life easier Preslav Mihaylov 16.10.2016, Java2Days Sofia, Bulgaria

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/PreslavMihaylov /PreslavMihaylov Software Engineer Technical Trainer /PreslavMihaylov

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 What is a shell  How do we interact with the shell  Introduction to Bash scripting  Exploring Bash script syntax  Real world issues  When not to use Bash  Exploring all the different commands  In-depth coverage of bash features Agenda

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What is a shell

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OS SHELL USER

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How do we interact with the shell Live Demo

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OK. So we can type in commands in the interactive shell

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But how do we automate them?

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Introduction to Bash scripting

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Moving from the command prompt To a text file Live Demo

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The shebang... #!/bin/bash  … defines the program which will interpret the script   … is stationed on the first line of the script 

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Redirecting I/O  One of the most powerful features   Allows us to combine programs together

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Keyboard echo Screen echo “Hello world”

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Keyboard echo Screen echo “Hello world” > log.txt log.txt

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Keyboard echo Screen grep “hello”

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echo Screen echo “Hello world” | grep “Hello” Screen grep Screen

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Live Demo

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Exploring Bash script syntax

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Variables  How to declare them:  STR=Hello   How to use them:  echo $STR

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How NOT to declare them  STR =Hello STR= Hello STR = Hello STR = Hello

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How NOT to use them  echo $STR_pesho   Correct way:  echo ${STR}_pesho

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Working with text  Parses text as is:  echo ’Hello $STR’   Interpolates text:  echo “Hello $STR”   Gets the output of the command:  echo “Hello $(cat name.txt)”

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Live Demo

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Making decisions  If ; then  ...  elif ; then  …  else  …  fi  Syntax:

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Making decisions  The condition format depends on the brackets used   The brackets can be of many kinds. Depending on them you can do arithmetic expressions, regex, etc...   A short tutorial:  Bash scripting if statements

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Live Demo

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Repetition structures  for var in list; do …  done   while ; do …  done  Syntax:

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Repetition structures  The list is a string with whitespace (depends on IFS) separated values   The var is a shell variable which acts as an iterator over the list   The condition works the same way it works with Decision structures

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Live Demo

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Real world issues

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Three points of view  The User   The Developer   The Sysadmin

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The User wants to...  … avoid tedious tasks.  … automate his daily tasks.  … customize his shell the way he wants.

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The Developer wants to...  … do his work in peace.  … build his project appropriately.  … tune up his OS a bit.

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The Sysadmin wants to...  … automate his work in order to play Counter Strike.  … maintain a stable system.  … avoid dealing with Users.

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Live Demo

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When not to use Bash

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Avoid using Bash...  … on Heavy tasks.  … when the script gets too big.

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Resources  TLDP - Intro Bash Scripting  TLDP - Advanced Bash Scripting  From Bash to Z Shell 

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The GUI makes the simple tasks - even simpler. The Shell makes the impossible tasks - possible

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May the Bash be with you /PreslavMihaylov /PreslavMihaylov /PreslavMihaylov 16.10.2016, Java2Days Sofia, Bulgaria