Basic concepts of linux

Day 8

Hello everyone welcome back !!!

Myself Swanik Santosh Gudekar and I am back with my blog. This is the eighth blog of Linux series. Today I attended the eighth session conducted by Master Pranav Jambare at Dr. Babasaheb Ambedkar Technological University.

Points Covered In This Session :

• Loops

• Common line argument

Loops :

• In Linux, loops are used to execute a set of commands repeatedly.

• The for loop is one of the most commonly used loops in Linux Bash scripts.

• It is very flexible and can work with numbers, words, arrays, command line variables or the output of other commands

Types of loops:

1) While loop :

• In Linux, the while loop is a type of loop that continues to execute as long as the programmed condition remains true.

• It is useful when you need to execute a set of instructions a certain number of times or when you want to create an infinite loop.

• SYNTAX :

while <condition1>
do 
    <condition2>
done

EXAMPLE :

#Program:

#!/bin/bash
 a=1
 while [ ${a} -le 10 ];
 do
     echo "Number is ${a}"
     a=`expr ${a} + 1` 
 done

#Output: 

 Number is 1
 Number is 2
 Number is 3
 Number is 4
 Number is 5
 Number is 6
 Number is 7
 Number is 8
 Number is 9
 Number is 10

2) for loop :

• A for loop in Linux is a way of repeating a set of commands for each item in a list or a range of values.

• The for loop is particularly useful for processing lists of items, filenames, or any other collection of data.

• SYNTAX :

    for var in word1 word2..wordn                  --(var=variable)
    do
        <condition>
    done
  

• EXAMPLE :

    #program:
  
     #!/bin/bash
  
     for numbers in {1..5};
     do
         echo " ${numbers} "
     done
  
     #Output
     1
     2
     3
     4
     5
  

  3) until loop :

• An until loop in Linux is a way of repeating a set of commands as long as a given condition is false.

• It is similar to a while loop but with the opposite logic.

• SYNTAX :

    until <condition>
    do
        statement executed if the command is true
    done
  

• EXAMPLE :

 #program:

 #!/bin/bash

 A=10
 until [ ${A} == 1 ];
 do
     echo "${A} is not equal to 1"
     A=`expr ${A} - 1` 
 done

# Output: 
 10 is not equal to 1
 9 is not equal to 1
 8 is not equal to 1
 7 is not equal to 1
 6 is not equal to 1
 5 is not equal to 1
 4 is not equal to 1
 3 is not equal to 1
 2 is not equal to 1

Common line argument :

• Common line arguments are the parameters that the user provides via the terminal to a script or a command, which uses them to perform a specific task according to user input.

• $1 $2 $3 : Arguments passed.

• $0 : Name of the shell program.

• $@ : One-by-one arguments passed.

• $# : Total number of arguments.

• $* : All arguments together.

• $$ : PID(Process ID) of current shell. (Actually, the program PID can be achieved).

• $? : Status of the last command.

• $! : PID of the last command*.*

These were the topics covered by Master Pranav Jambare in the eighth session of Linux. Thankyou for reading my blog and also do check out my previous blogs !!