Bash script loop through file line by line

With this script: echo "Start! Improve this question. Meraj al Maksud 1, 2 2 gold badges 20 20 silver badges 34 34 bronze badges. Peter Mortensen Peter Mortensen Oh, I see many things have happened here: all the comments were deleted and the question being reopened.

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. Add a comment. Active Oldest Votes. Improve this answer. How should I interpret the last line? File peptides. This method seems to skip the last line of a file. Double quote the lines!! I KNOW! Both versions fail to read a final line if it is not terminated with a newline.

Show 16 more comments. You can avoid this by the following: cat peptides. Warren Young Warren Young In general, if you're using "cat" with only one argument, you're doing something wrong or suboptimal. Yes, it's just not as efficient as Bruno's, because it launches another program, unnecessarily.

If efficiency matters, do it Bruno's way. I remember my way because you can use it with other commands, where the "redirect in from" syntax doesn't work. There's another, more serious problem with this: because the while loop is part of a pipeline, it runs in a subshell, and hence any variables set inside the loop are lost when it exits see bash-hackers.

This can be very annoying depending on what you're trying to do in the loop. I use "cat file " as the start of a lot of my commands purely because I often prototype with "head file " — mat kelcey. This may be not that efficient, but it's much more readable than other answers. Show 13 more comments. Option 1a: While loop: Single line at a time: Input redirection! Stan Graves Stan Graves 6, 2 2 gold badges 17 17 silver badges 14 14 bronze badges.

For option 1b: does the file descriptor need to be closed again? The file descriptor will be cleaned up with the process exits.

An explicit close can be done to reuse the fd number. Thank you for Option 2. I ran into huge problems with Option 1 because I needed to read from stdin within the loop; in such a case Option 1 will not work. You should point out more clearly that Option 2 is strongly discouraged.

Show 2 more comments. Best of luck! If you know for a fact there are no spaces, then a line equals a word and you're okay. JoaoCosta,maxpolk : Good points that I hadn't considered.

I've edited the original post to reflect them. Have you tried that version? The way how this command gets a lot more complex as crucial issues are fixed, presents very well why using for to iterate file lines is a a bad idea. Plus, the expansion aspect mentioned by mklement0 even though that probably can be circumvented by bringing in escaped quotes, which again makes things more complex and less readable. Show 6 more comments. Reading from a null delimited input, for example find Related posts: Creating an array from a text file in Bash What is the difference between thee approaches to reading a file that has just one line?

Bash while read loop extremely slow compared to cat, why? I knew there was a way to do it without programming it. Actually programming it would make it look cleaner.

It is easy to do and the system calls are inside the executable. Comments 6 bash. GoofProg says: Reply June 3, at am.

Raghubir says: Reply February 9, at am. Cookie information is stored in your browser and performs functions such as recognising you when you return to our website and helping our team to understand which sections of the website you find most interesting and useful.

Strictly Necessary Cookie should be enabled at all times so that we can save your preferences for cookie settings. If you disable this cookie, we will not be able to save your preferences. This means that every time you visit this website you will need to enable or disable cookies again. Skip to content I want to loop through the lines of a file with a Bash script and one of the ways to do it is using a for loop. What is a for loop? The logic executed is every time the same and the only thing that changes is the city.

The N commands between do and done are executed for each item in the list. For Loop in Bash In this article you will learn how to use the for loop in Bash and specifically to go through the lines of a file. But why would you do that? Going through the lines of a file? In this example we will use a simple. Below you can see the format of the text file, a colon is used to separate each city from the number of people who live in that city: Istanbul,, Moscow,, London:9,, So, how can we use a Bash for loop to go through the content of this file?

Here is the final script:! This means we can use any commands we want to generate the LIST to be passed to the for loop. Do you have in mind any other possible commands? What is a Counter in a Bash For Loop? Then at each iteration I print the value of the counter together with the line from the file. The two statements that allow to do that are break and continue : break : interrupts the execution of the for loop and jumps to the first line after for loop.

The break statement inside the if breaks the execution of the loop if the counter is equal to 3:! This is not a suggested practice considering that it makes your code less readable.