Day 8 Task: Shell Scripting Challenge

Tasks:

Task 1: Comments

In shell scripting, comments are used to annotate the code, making it easier to understand and maintain. Comments are ignored by the shell during execution. Here's how to use comments in shell scripts:

Single-Line Comments

• Use the # symbol to start a comment. Everything after the # on that line is treated as a comment.

    #!/bin/bash 
  
    # Below we are printing the present working directory 
  
    present_dir=$(pwd)
  
    echo "${present_dir}"
  

  Multi-Line Comments

• You can achieve multi-line comments by using a sequence of single-line comments.

     #!/bin/bash
  
    << COMMENT 
    This is multi line comment
    we declare one variable present_dir to retrive present working directory
    and then we print that in our console by echo
    COMMENT
  
    present_dir=$(pwd)
  
    echo "${present_dir}"
  

Task 2: Echo

The echo command in a shell script is used to display text or output on the terminal. It is one of the most commonly used commands in shell scripting for printing messages, variable values, and other information.

#!/bin/bash

present_dir=$(pwd) 

# below we are printing the present directory in the output screen
echo "${present_dir}"

Task 3: Variables

Variables in shell scripting are used to store and manipulate data. They are an essential part of writing scripts, enabling you to work with data dynamically.

#!/bin/bash

# This the variable num1 which stores the value 6
num1=6

#This is the another variable num2 which stores the value 5
num2=5

# we are declaring sum variable to store the addition of two number

sum=$((num1+num2))

#Printing the value of sum in the screen 

echo "${sum}"

Task 5: Using Built-in Variables

Built-in variables in shell scripting are special variables that are predefined by the shell and hold useful information about the environment, script execution, and user inputs. These variables are automatically set by the shell and can be used in scripts without any prior definition.

#!/bin/bash

# This script will simply print its name

echo "name of the script is: $0"

sleep 30 &
echo "Process ID of last command: $!"

Task 6: Wildcards

Wildcards are special characters used to perform pattern matching when working with files.

#!/bin/bash

# Variable takes an input through an argument 

WORKING_DIR=$1                       #/path/pathof directory

# This will take all your files with a particular extension 

EXTENSION1=$2
EXTENSION2=$3

#Command 

listing=$(ls -l "${WORKING_DIR}"/*"${EXTENSION1}" "${WORKING_DIR}"/*"${EXTENSION2}")

echo ${listing}