Use nano to work on loops and save them as shell scripts. Here is a sample cat file.txt... (4 Replies) Here we will see what kind of loops can be used for reading a file. Just for reference, the accepted answer in Read a file line by line assigning the value to a variable addresses the problem in a canonical way and should be preferred over the accepted one here. The file contains 3 fields: OS, the company and a random value. The concepts of loop are to implement these repetitive task through code and create powerful constructs through codes without any human intervention. – fedorqui 'SO stop harming' Aug 30 '16 at 9:44 All these solve different purposes on when to assign values to variables. check if a directory is empty or not in shell script; loop through files in a directory in shell script; replace last n characters of a string in shell script; check if a file is empty in shell script; keyboard shortcuts for moving cursor on command line; Read from file in shell script; create symbolic link in linux; shell date examples; More What is Shell Script Read File? The read command is useful for assigning variables at the time of executing a script, a kind of interactive script. Just to ground the syntax and workings of the for-loop, here's the thought process from turning a routine task into a loop: Let's break the script down. In a BASH for loop, all the statements between do and done are performed once for every item in the list. I am writing a shell script using the korn shell. Oh, I see many things have happened here: all the comments were deleted and the question being reopened. Using a while loop coupled with a read statement is a perfect way to accomplish this task. (I can't access a variable outside a previously used while loop.) For longer files, I'll work on my computer's text editor (Sublime Text) and then upload to the server. It seems that I am only able to use local variables within a while loop that is reading a file. Let's break the script down. Overview of Unix Shell Loops and Different Loop Types like: Unix Do While Loop; Unix For Loop; Unix Until Loop; In this tutorial, we will cover the control instructions that are used to iterate a set of commands over a series of data. Let us consider a file with sample contents as shown below. Exercise with web scraping. This article will also explain the usage of shell while loop. Unix/Linux shell script FAQ: How do I write a Unix or Linux shell script where I “do something” for every line in a text file? The Bash way of using for loops is somewhat different from the way other programming and scripting languages handle for loops. The following shell script will prompt the user to enter a file name and then it will read the file content line by line using the while loop and will assign each line into a variable and then it will print on the screen. Example 3 - How to write a UNIX shell script with a while loop that reads each line in a text file Shell scripts will frequently need to read the contents of a file, line by line, and store each line in a shell variable for additional processing. 1. Learn read command with examples The read command syntax When running a script: We can assign values to variables when we are in middle of the script. Solution: A simple way to process every line in a text file is to use a Unix/Linux while loop in combination with the Linux cat command , like this: ) and also incremented the value of (i) inside the loop and at the end I am getting the wrong value of i, the main reason is that the usage of pipe (|) will create a new sub-shell to read the file and any operation you do within this while loop (example – i++) will get lost when this sub-shell … It's been a while since I wrote shell scripts. There are eventually 2 loops through which it is possible to read a file. For loop Let us see in this article how to read and parse a file field by field or column by column and extract data from it using the while loop of shell. On many Unix (but not GNU/Linux) systems, this can also be done as: while3b.sh #!/bin/sh while f=`line` do .. process f .. done < myfile But since the while read f works with any *nix, and doesn't depend on the external program line , the former is preferable. 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