Let's break the script down. When running a script: We can assign values to variables when we are in middle of the script. – fedorqui 'SO stop harming' Aug 30 '16 at 9:44 Oh, I see many things have happened here: all the comments were deleted and the question being reopened. Here we will see what kind of loops can be used for reading a file. 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? 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. 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. 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? It's been a while since I wrote shell scripts. (I can't access a variable outside a previously used while loop.) Use nano to work on loops and save them as shell scripts. I am writing a shell script using the korn shell. 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. ) 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 … This article will also explain the usage of shell while loop. In a BASH for loop, all the statements between do and done are performed once for every item in the list. Exercise with web scraping. The Bash way of using for loops is somewhat different from the way other programming and scripting languages handle for loops. Let us consider a file with sample contents as shown below. Just to ground the syntax and workings of the for-loop, here's the thought process from turning a routine task into a loop: The read command is useful for assigning variables at the time of executing a script, a kind of interactive script. Read a File Line by Line Using Shell Script. Learn read command with examples The read command syntax Using a while loop coupled with a read statement is a perfect way to accomplish this task. 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. Let's break the script down. It seems that I am only able to use local variables within a while loop that is reading a file. For loop All these solve different purposes on when to assign values to variables. 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. The concepts of loop are to implement these repetitive task through code and create powerful constructs through codes without any human intervention. There are eventually 2 loops through which it is possible to read a file. The file contains 3 fields: OS, the company and a random value. 1. Here is a sample cat file.txt... (4 Replies) 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: For longer files, I'll work on my computer's text editor (Sublime Text) and then upload to the server. 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