Changes between Version 7 and Version 8 of Csle2022/Agenda/scriptingandgithub

Timestamp:

Nov 1, 2022, 2:14:27 PM (3 years ago)

Author:

deepthi

Comment:

--

Csle2022/Agenda/scriptingandgithub

@@ -13 +13 @@
 - For executing the script type bash filename.sh.
 
+File Color : Executable scripts appear in a different colour from rest of the files and folders.
+
+Let's start to have some experience on scripting
+
+===== Simple Script for newbies =====
+
+First we have to create a text file
+
+`$cat > hello.sh`
+
+And create the content in it
+
+#!/bin/sh 
+echo 'Hello World'
+
+`#!/bin/sh` is "how to run" the program.
+`echo 'Hello World'` is "what to do" in the script
+
+Then make the file executable
+
+`$ chmod +x hello.sh`
+
+And run the executable file
+
+`$./hello.sh`
+
+Output:
+
+Hello world
+
+Make yourself familiar with `man man` and `man apropos` on the shell. It will need for your self-tutoring.
+
+==== Let's make this little advanced ====
+
+===== How to define variables =====
+
+Variables can be defined using the syntax ` variable_name=value`. To get the value of the variable, add `$` before the variable
+
+#!/bin/bash
+# A simple variable example
+greeting=Hello
+name=world
+echo $greeting $name
+
+===== Arithmetic Expressions =====
+
+These are the operstors supported by bash for mathematical calculations.
+
++       addition
+-       subtraction
+*       multiplication
+/       division
+**      exponentiation
+%       modulus
+
+Numerical expressions can also be calculated and stored in a variable using the syntax below:
+
+`value=$((expression))`
+
+#!/bin/bash
+
+var=$((3+9))
+echo $var
+
+===== How to read user input =====
+
+Sometimes user input are needed to perform relevant operations.
+
+In bash, user inputs are taken using the` read` command.
+
+`read variable_name`
+
+To prompt the user with a custom message, use the `-p` flag.
+
+`read -p "Enter your age" variable_name`
+
+===== Numeric Comparison logical operators =====
+
+Comparison is used to check if statements evaluate to true or false. 
+
+Equality                        num1 -eq num2   is num1 equal to num2
+Greater than equal to   num1 -ge num2   is num1 greater than equal to num2
+Greater than                    num1 -gt num2   is num1 greater than num2
+Less than equal to              num1 -le num2   is num1 less than equal to num2
+Less than                       num1 -lt num2   is num1 less than num2
+Not Equal to                    num1 -ne num2   is num1 not equal to num2
+
+Syntax:
+
+if [ conditions ]
+    then
+         commands
+fi
+
+===== Conditional Statements (Decision Making) =====
+
+Conditions are expressions that evaluate to a boolean expression (true or false). To check conditions, we can use `if`,` if-else`,` if-elif-else` and nested conditionals.
+
+===== Looping and skipping =====
+
+For loops allow you to execute statements a specific number of times. 
+
+Looping with numbers:
+
+#!/bin/bash
+
+for i in {1..5}
+do
+    echo $i
+done
+
+Looping with strings:
+
+#!/bin/bash
+
+for X in cyan magenta yellow  
+do
+        echo $X
+done
+
+====== While loop ======
+
+While loops check for a condition and loop until the condition remains true. We need to provide a counter statement that increments the counter to control loop execution.
+
+#!/bin/bash
+i=1
+while [[ $i -le 10 ]] ; do
+   echo "$i"
+  (( i += 1 ))
+done
+
+Reading files: 
+
+Suppose we have a file sample_file.txt as shown below:
+
+#!/bin/bash
+
+LINE=1
+
+while read -r CURRENT_LINE
+        do
+                echo "$LINE: $CURRENT_LINE"
+    ((LINE++))
+done < "sample_file.txt"
+
+
+
 == Github administration ==