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5 UNIX for and while Loop Examples...with Sample Shell Scripts!!! 5 UNIX for and while Loop Examples...with Sample Shell Scripts!!!

5 UNIX for and while Loop Examples...with Sample Shell Scripts!!!

UNIX shell script for and while loops are key weapons in every shell programmer's arsenal. Although there are two additional looping constructs, select and until, I have almost always been able to efficiently accomplish my UNIX shell scripting objectives with either a for loop or a while loop. Come to think of it, I do not recall ever having the need to use a select or until loop in any shell scripts that I've written in the past. It's very possible that the positions I've worked in, and therefore the shell scripting related tasks I've needed to complete, didn't require the use of select or until loops but I'm sure that both constructs serve an important role...somewhere.

How to Run or Repeat a Linux Command Every X Seconds Forever. A system administrator often needs to run a command repeatedly in a certain periods of time.

How to Run or Repeat a Linux Command Every X Seconds Forever

Often such tasks can be easily completed with simple cron commands. In most of the cases this should work, but the shortest period which you can run cron command is every 1 minute. The Bash For Loop, The First Step in Automation on Linux. I believe mastering the for loop in Bash on Linux is one of the fundamentals for Linux sysadmins (and even developers!)

The Bash For Loop, The First Step in Automation on Linux

That takes your automation skills to the next level. In this post I explain how they work and offer some useful examples. Update 07/06/2016: lots of critique on Reddit (granted: well deserved), so I updated most of the examples on this page for safer/saner defaults. Let me first start by saying something embarrassing. For the first 4 or 5 years of my Linux career -- which is nearing 10 years of professional experience -- I never used loops in Bash scripts. Bash One Liner that uses multiple variables. Posted by Josh on November 17, 2011 I’m not sure if this particular post will come in handy to a lot of people, but my bash scripting is still pretty weak and I think the best way to commit this to memory will be to write a short post on it.

Bash One Liner that uses multiple variables

I find myself doing one line “for” statements from the command line all the time to make quick loops. Shell tricks for one-liner bioinformatics. There is always more than one way to accomplish a computational task, but some solutions are better than others.

Shell tricks for one-liner bioinformatics

For bioinformatics processing, we want solutions that are easy and quick to implement and efficient enough to get the job done quickly. You can always write a simple program, but for many tasks, using Linux/Unix shell commands provides quick solutions, without the need to explicitly open/parse files, set up data structures, etc. Instead, a one-liner command in your shell takes care of the overhead so that you write a small amount of code and move on. The examples below are meant to illustrate some of the most useful shell commands for bioinformatics processing. For and Read-While Loops in Bash. The loop is one of the most fundamental and powerful constructs in computing, because it allows us to repeat a set of commands, as many times as we want, upon a list of items of our choosing.

For and Read-While Loops in Bash

Much of computational thinking involves taking one task and solving it in a way that can be applied repeatedly to all other similar tasks, and the for loop is how we make the computer do that repetitive work: for item in $itemsdo task $itemdone Unlike most of the code we've written so far at the interactive prompt, a for-loop doesn't execute as soon as we hit Enter: user@host:~$ for item in $items We can write out as many commands as we want in the block between the do and done keywords:

One line bash Archives - In bash, there area number of ways you can write loops.

one line bash Archives -

Here, we’ll look at putting a single line with a loop in it. This will be done using the for command. For requires a do and a done. The do is what we’ll do for each iteration. Here, we’ll just run a loop from 1 to 10 and then we’ll do an echo on that variable so it displays on the screen as well loop: The classic for-loop. Synopsis for <NAME>; do <LIST> done for <NAME> in <WORDS>; do <LIST> done alternative, historical and undocumented syntax 1) for <NAME>; { <LIST> } for <NAME> in <WORDS>; { <LIST> }

The classic for-loop

Loops. The for loop. 9.1.1.

The for loop

How does it work? The for loop is the first of the three shell looping constructs. Penguin Pete's Blog - How the One-Liner For-Loop in Bash Goes. Every now and then when I'm pecking around on the Linux command line, I have a need to perform the same operation on a whole group of files.

Penguin Pete's Blog - How the One-Liner For-Loop in Bash Goes

The syntax for doing so is something I always have to look up. It's one of those jobs that aren't important enough to write a shell script for, and not common enough that I'll remember it next time. HowTo: Use bash For Loop In One Line - Daniel Han's Technical Notes. How To Read a Linux File Line by Line. This article will introduce the concept of playing a file line by line in Linux with the help of examples and best user tips. We'll walk you through some of the most common errors made when reading a file on the Linux platform, and show you examples of how the for loop and while loop outputs differ. We'll also provide you with some tips and examples on how to initiate a loop, and how to use the while loop output. How To Read a File Line by Line. Bash for-each line 1-liners. Note: Examples run on Solaris 5.10. input.txt contains the following three lines: Suppose you want to do something for each line in file. The most obvious way is to use a for loop - it almost matches how you think about it!

So lets try (input line followed by output): Bash for loop. Definitions Loops are very important when programming, that is the way you can take full advantage of the speed of computers to solve different problems. Computers are great at doing repetitive task, and they are fast too. I can still remember when being a child I started coding with Basic (Yes the old Basic), and Do…While, Do…Until and For were some of the most important lessons learned, together with IF statement. Now, that I use Linux and Mac OSX a lot, I take full advantage of For…Loop. Specially when working with a lot of files at a time.

Loops - Bash Scripting Tutorial. Loops! Round and round we go. Introduction Bash loops are very useful. In this section of our Bash Scripting Tutorial we'll look at the different loop formats available to us as well as discuss when and why you may want to use each of them. Loops allow us to take a series of commands and keep re-running them until a particular situation is reached. 5 Bash for loop examples to make command line tasks more efficient. One of the things that excited me while learning Unix/Linux was how quickly one can perform tasks via the command line. Bash is a fully functional scripting language that incorporates Variables, Loops and If/Then statements; the bash shell allows a user to use these functions while performing adhoc tasks via the command line.

This is also true for the other common shells such as bourne, korn shell, and csh. Below I will show 5 example for loops that are run on the command line without being placed into a shell script. These commands will show how one can use a for loop to accomplish an adhoc repetitive task quickly and efficiently. Bash For Loop Examples.