Because cat prints a file line-by-line, the following for loop seems sensible: For loop in which the loop should be continuously executed with as many number of lines the file.txt has In each loop execution, the respective line should be considered a input for the execution. For more in-depth discussion see this StackOverflow discussion: How to use "while read" (Bash) to read the last line in a file if there’s no newline at the end of the file? Get code examples like "bash read file line by line for loop" instantly right from your google search results with the Grepper Chrome Extension. For the most part, I'm going to try to avoid assigning problems that would involve this kind of logic, as it can be tricky to untwist during debugging. The syntax is as follows to run for loop from the command prompt. Let’s create a readfile.sh script. HowTo: Use bash For Loop In One Line. Stack Overflow for Teams is a private, secure spot for you and your coworkers to find and share information. Method 1: Using Input Redirector. Run Command 5 Times. Q&A for Work. for i in {1.. 5}; do COMMAND-HERE; done. For example, the following line-counting script prints 0 in these shells: Read File Using Bash Script. for each line that is a line in str, statements from do till done are executed, and line could be accessed within the for loop for respective iteration. When using for loops in bash it splits the given list by default by whitespaces, this can be adapted by using the so called Internal Field Seperator, or IFS in short . nano readfile.sh H ow do I use bash for loop in one line under UNIX or Linux operating systems? How does one properly iterate over lines in bash either in a variable, or from the output of a command? In this example, n variable is used to keep the value of the line number of the file and while loop is used to read this file with line number. Beware: this approach adds an additional newline to the last line if there is none already. OR. Author: Vivek Gite Last updated: June 7, 2011 10 comments. Teams. Here we learn 3 methods in a bash script to read file line by line. When writing a bash script, depends on the automation flow sometimes the script has to read the content from the file line by line. bash documentation: Looping through the output of a command line by line IFS The Internal Field Separator that is used for word splitting after expansion and to split lines into words with the read builtin command. Simply setting the IFS variable to a new line works for the output of a command but not when processing a variable that contains new lines. The simplest way to read a file line by line is by using the input redirector in a while loop. Note that in some shells (ash, bash, pdksh, but not ksh or zsh), the right-hand side of a pipeline runs in a separate process, so any variable you set in the loop is lost. Loops-within-loops is a common construct in programming. 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