Bash Loops {For, Until and While Loops}

In this video, we have talked about 3 kind of loops:
1- While Loops (01:46)
2- Until Loops (07:16)
3- For Loops (08:44)

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Bash For Loop,The Standard Bash for Loop

Loops are one of the fundamental concepts of programming languages. Loops are handy when you want to run a series of commands over and over again until a certain condition is reached.

In scripting languages such as Bash, loops are useful for automating repetitive tasks.

There are three basic loop constructs in Bash scripting, for loop, [while](https://linuxize.com/post/bash-while-loop/) loop, and [until](https://linuxize.com/post/bash-until-loop/) loop.

In this tutorial, we will cover the basics of for loops in Bash. We will also show you how to use the break and continue statements to alter the flow of a loop.

The Standard Bash for Loop

The for loop iterates over a list of items and performs the given set of commands.

The Bash for loop takes the following form:

for item in [LIST]
do
  [COMMANDS]
done

Copy

The list can be a series of strings separated by spaces, a range of numbers, output of a command, an array, and so on.

Loop over strings

In the example below, the loop will iterate over each item in the list of strings, and the variable element will be set to the current item:

for element in Hydrogen Helium Lithium Beryllium
do
  echo "Element: $element"
done

#bash #loop #bash for loop

Bash until Loop and Bash until Loop Example

Loops are one of the fundamental concepts of programming languages. Loops are handy when you want to run a series of commands over and over again until a specific condition is met.

In scripting languages such as Bash, loops are useful for automating repetitive tasks. There are 3 basic loop constructs in Bash scripting, [for](https://linuxize.com/post/bash-for-loop/) loop, [while](https://linuxize.com/post/bash-while-loop/) loop, and until loop.

This tutorial explains the basics of the until loop in Bash.

Bash until Loop

The until loop is used to execute a given set of commands as long as the given condition evaluates to false.

The Bash until loop takes the following form:

until [CONDITION]
do
  [COMMANDS]
done

Copy

The condition is evaluated before executing the commands. If the condition evaluates to false, commands are executed. Otherwise, if the condition evaluates to true the loop will be terminated and the program control will be passed to the command that follows.

In the example below, on each iteration the loop prints the current value of the variablecounterandincrements the variableby one.#!/bin/bash

counter=0

until [ $counter -gt 5 ]
do
  echo Counter: $counter
  ((counter++))
done

Copy

The loop iterates as long as the counter variable has a value greater than four. The script will produce the following output:

Counter: 0
Counter: 1
Counter: 2
Counter: 3
Counter: 4
Counter: 5

Use the [break](https://linuxize.com/post/bash-break-continue/) and [continue](https://linuxize.com/post/bash-break-continue/) statements to control the loop execution.

#bash #loop #bash until loop

Practical Bash: Variables and For Loops in Scripts - Beyond Code Live 009

Using variables and loops we can write scripts that work on a large set of files without writing it all out by hand.

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https://youtu.be/cp6KJKBZq50

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How to Use If-Else Statements and Loops in R – Dataquest

When we’re programming in R (or any other language, for that matter), we often want to control when and how particular parts of our code are executed. We can do that using control structures like if-else statements, for loops, and while loops.

Control structures are blocks of code that determine how other sections of code are executed based on specified parameters. You can think of these as a bit like the instructions a parent might give a child before leaving the house:

“If I’m not home by 8pm, make yourself dinner.”

Control structures set a condition and tell R what to do when that condition is met or not met. And unlike some kids, R will always do what we tell it to! You can learn more about control structures in the R documentation if you would like.

In this tutorial, we assume you’re familiar with basic data structures, and arithmetic operations in R.

Not quite there yet? Check out our Introductory R Programming course that’s part of our Data Analyst in R path. It’s free to start learning, there are no prerequisites, and there’s nothing to install — you can start learning in your browser right now.

install.packages(“Dataquest”)

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(This tutorial is based on our intermediate R programming course, so check that out as well! It’s interactive and will allow you to write and run code right in your browser.)

Comparison Operators in R

In order to use control structures, we need to create statements that will turn out to be either TRUE or FALSE. In the kids example above, the statement “It’s 8pm. Are my parents home yet?” yields TRUE (“Yes”) or FALSE (“No”). In R, the most fundamental way to evaluate something as TRUE or FALSE is through comparison operators.

Below are six essential comparison operators for working with control structures in R:

• == means equality. The statement x == a framed as a question means “Does the value of x equal the value of a?”
• != means “not equal”. The statement x == b means “Does the value of x not equal the value of b?”
• < means “less than”. The statement x < c means “Is the value of x less than the value of c?”
• <= means “less than or equal”. The statement x <= d means “Is the value of x less or equal to the value of d?”
• > means “greater than”. The statement x > e means “Is the value of x greater than the value of e?”
• >= means “greater than or equal”. The statement x >= f means “Is the value of xgreater than or equal to the value of f?”

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Python For Loop (with Examples)

A Python tutorial to understand the uses of for loop in various ways including examples.

Python is a general-purpose programming language, which emphasizes making programming easy, efficient coding, and unleashes the user’s potential. Loops are the vital part of programming as it allows the user to repetitive use a set of codes using loops. So in the following article, we will see how to use for loops in python.

FOR Loop:

Till the iteration of the last item in the sequence, for loop run the instructions. It iterates over sets of instructions in sequence, arrays, and a tuple for a pre-defined period or until the last item and calculation are executed.

For loop can be categorized in three ways.

1. Traditional for loop – It is usually used in programming language and contains three parts of a loop, i.e., initialization, condition, increment/decrement.
2. Iterator/collection-based for loop – It is used for the iteration of objects and collections instead of numbers.
3. Vectorize for loop – It is used to iterate parallel arrays simultaneously.

#python #for loop #loops #loop #python for loop