Bash Conditionals

Conditionals are used when you must make some decision (to execute some part of code or not) by evaluating expression in your script.
For conditionals in Bash scripting language are used clauses: if, then, else.

if (some expression)
then
(do some code)
else
(do some code)

Simplest example is use only if,then

if ["$Var1" = "$Var2"]; then
echo "Variables Var1 and Var2 are equal!"
fi

with clause fi we close if statement.

Other example:

if ["$Var1" = "$Var2"]; then
echo "Variables Var1 and Var 2 are equal!"
else
echo "Variables Var1 and Var2 are NOT equal!"
fi

Variables in Bash script

Variables in Bash script language have following properties:

• They haven't data type
• There is no need to declare variable

So, let's see how they works on simple "Hello World" Example:

#!/bin/bash
Var1 = "Hello World!"
echo $Var1

This simple example will output sentence Hello World!

 Interesting with $ sign in Bash is, if you put something in brackets after $ this will be interpreted as interpreter command.

#!/bin/bash
Var1= $(ls -la)
echo $Var1

This simple example will put output from ls -la command in $Var1 variable and then print content on screen.

Important thing about variables is that you can use local variables in functions, using keyword local.

local Var1="Local variable"

Builtin variables

 

 Bash have Built-in variables, some of them are:

• $BASH - Path to the Bash binary
• $BASHPID - Process ID of Bash 
• $BASH_VERSION - Version of Bash
• $HOME - Home directory of user
• $MACHTYPE - Machine type
• $PATH - Path to binaries
• $PWD - Working directory
• $SECONDS - number of second while script is running
• $UID - User ID number
• $0,$1 ... - Command line arguments
• $# - Number of command line arguments

And many more... 

Bash - Count words in text and make dictionary

In this tutorial i'll try to explain how to count words in some text and make list of used words.

First we could get some text file. I get War and Peace by Leo Tolstoy from Project Gutenberg:

wget http://gutenberg.org/files/2600/2600.txt

After getting file, we must to convert uppercase letters to lowercase:

tr A-Z a-z

then convert everything which is not small letter to new line

tr -cs a-z '\n'

then sort result

sort

finally get unique words and count them:

uniq -c

To get this into working condition we must put those commands into pipeline. To do that we'll make file wordcount:

nano wordcount

and type this:

cat "$@" | tr A-Z a-z | tr -cs a-z '\n'|sort|uniq -c

save and exit nano editor.
Give executable rights to file wordcount:

chmod +x wordcount

and count words with

./wordcount <textfile>

in this case:

./wordcount 2600.txt

and we'll get words used in this great book and their number of appearances.

If we want to get only dictionary used in this book, we make another file:

nano makedict

and type this:

cat "$@" | tr A-Z a-z | tr -cs a-z '\n'|sort|uniq

take note that only difference between wordcount and makedict scripts is -c switch in uniq command.
of course, we must give execution rights to file:

chmod +x makedict

and use:

./makedict 2600.txt

Mandelbrot fractal zoom animation

Experiment with fractal. Zooming around (-0.234107006,-0.861307916).