Create II Variables in Bash Scripting.py

Author: ortizfram

Introduction to Bash Scripting/II Variables in Bash Scripting.py

@@ -0,0 +1,118 @@
+"""
+In this chapter, you’ll learn how to create basic string and numeric variables, and perform calculations on these variables. 
+You’ll also learn about the magic of a shell-within-a-shell (shell-ception), opening up huge opportunities for advanced scripting.
+"""
+
+"""
+*** Basic variables in Bash
+    >>>>>> var1="moon" : asign a variable
+    >>>>>> echo $var : reference variable with notation 
+      
+      *** single, double, backticks
+          >>>>>> 'text'  : literally what's in between
+          >>>>>> "$text or `text` o $(text)"  : literally except using [$] and [backticks], just to be printed out
+          >>>>>> `text`  : runs and captures STDOUT back into variable
+          
+          eg: var="the day is `date`"
+              echo $var
+              
+              the day is 02/11/22 16:51
+              
+"""
+
+"""
+### Using variables in Bash
+
+-Create a variable, yourname that contains the name of the user. Let's use the test name 'Sam' for this.
+-Fix the echo statement so it prints the variable and not the word yourname.
+-Run your script.
+
+"""
+# Create the required variable
+yourname="Sam"
+
+# Print out the assigned name (Help fix this error!)
+echo "Hi there $yourname, welcome to the website!"
+
+
+repl:~/workspace$ bash script.sh
+Hi there Sam, welcome to the website!
+
+"""
+### Shell within a shell
+ 
+-Which of the following correctly uses a 'shell within a shell' to print out the date? 
+  We do not want to select the option that will just print out the string 'date'.
+  
+Answer : echo "Right now it is `date`"
+
+"""
+
+"""
+### Numeric variables in Bash
+
+*** for num vars we must use : 
+    >>>>>> expr
+    
+    eg : expr 5+4
+         9
+         
+    *** expr LIMITATIONS : don't handle decimals
+*** for decimal vars :
+    >>>>>> bc (basic calculator)
+    
+    eg: 
+        # echoing and piping bc
+        echo "5 + 7.5" | bc
+        12.5
+        
+        # echo calculation piped to bc for filling string results
+        model1=87.65
+        model2=89.20
+        echo "Score is $(echo "model1 + model2" | bc)"
+        score is 176.85
+        
+*** for specifying decimal places : 
+    >>>>>> scale
+    
+    eg: echo "scale=3; 10/3" | bc
+        3.333
+"""
+
+"""
+### Converting Fahrenheit to Celsius
+
+-Your task is to write a program that takes in a single number (a temperature in Fahrenheit) as an ARGV argument, converts it to 
+ Celsius and returns the new value. There may be decimal places so you will need to undertake calculations using the bc program.
+-At all times use 2 decimal places using the scale command for bc.
+-The formula for Fahrenheit to Celsius is:
+
+The formula for Fahrenheit to Celsius is:
+C = (F - 32) x (5/9)
+
+"""
+# Get first ARGV into variable
+temp_f=$1
+
+# Subtract 32
+temp_f2=$(echo "scale=2; $temp_f - 32" | bc)
+
+# Multiply by 5/9
+temp_c=$(echo "scale=2; $temp_f2 * 5 / 9" | bc)
+
+# Print the celsius temp
+echo $temp_c
+
+
+repl:~/workspace$ bash script.sh 108
+42.22
+
+"""
+### Extracting data from files
+
+Your task is to extract the data from each file (by concatenating) into the relevant variable and print it out. 
+The temperature in the file region_A needs to be assigned to the variable temp_a and so on.
+
+-Create three variables from the data in the three files within temps by concatenating the content into a variable using a shell-within-a-shell.
+-Print out the variables to ensure it worked.
+-Save your script and run from the command line.