Linux reading text file

Master the Command Line: A Comprehensive Guide to Reading Text Files in Linux

Learn how to read text files in Linux via the command line using commands such as `cat`, `head`, `less`, `more`, and `grep`. Improve your Linux skills now!

• Cat Command
• Head Command
• How to Display Contents Of A Text File On Command Line Linux
• Less Command
• More Command
• Read Command
• Other useful code examples for reading text files in Linux
• Conclusion
• How do I read a text file in Unix?
• How do I open a text file in command prompt?
• How do you find a .TXT file in Linux?
• How do I view the contents of a file in terminal?

As a software developer or IT professional, mastering the command line is an essential skill. When it comes to Linux, one of the most popular operating systems out there, understanding how to read text files via the command line is particularly important. In this blog post, we will provide a comprehensive guide on how to read text files in Linux via the command line, including commands such as cat , head , less , more , and grep .

Cat Command

The cat command is the most popular command to view a file in Linux. It is short for “concatenate” and is used to display the entire contents of a file in the terminal. To use the cat command, simply type cat filename in the terminal. Here’s an example:

This command displays the entire contents of the file in the terminal. While the cat command is useful for small files, it is not recommended for larger files because it can quickly become difficult to navigate through the output.

Head Command

The head command is used to print the starting lines of any text file. It is particularly useful for quickly previewing the contents of a file without having to display the entire file. To use the head command, simply type head filename in the terminal. By default, head displays the first 10 lines of the file. Here’s an example:

This command displays the first 10 lines of the file in the terminal. If you want to display a different number of lines, you can use the -n flag followed by the number of lines you want to display. For example, to display the first 5 lines of a file, you would type:

How to Display Contents Of A Text File On Command Line Linux

how to display contents of a file in linux . Linux Basics: How to Show File Contents#Ubuntu Duration: 9:48

Less Command

The less command is another popular command for viewing the contents of a file in Linux. It shows the text file one screen at a time, allowing you to navigate through the file using the arrow keys. To use the less command, simply type less filename in the terminal. Here’s an example:

This command displays the file one screen at a time, starting with the first line. You can navigate through the file by using the up and down arrow keys. If you want to search for a specific string in the file, you can use the / key followed by the string you want to search for. For example, to search for the word “apple” in a file, you would type:

More Command

The more command is similar to the less command. It is used to display the contents of a file one screen at a time. To use the more command, simply type more filename in the terminal. Here’s an example:

This command displays the file one screen at a time, starting with the first line. You can navigate through the file by pressing the spacebar to display the next screen or the enter key to display the next line. If you want to search for a specific string in the file, you can use the / key followed by the string you want to search for, just like with the less command.

Read Command

The read command is used to read a file line by line on a Bash Unix & Linux shell. To use the read command, simply type while read line; do echo $line; done < filename in the terminal. Here’s an example:

while read line; do echo $line; done < file.txt 

This command reads the file line by line and displays each line in the terminal. It is particularly useful for large files because it only displays one line at a time, making it easier to navigate through the output.

Other useful code examples for reading text files in Linux

In Shell case in point, linux read text file command line code example

In Shell as proof, txt file open command linux code sample

### you can use less filename.txt

Conclusion

In conclusion, there are several commands available for reading text files in Linux via the command line, including cat , head , less , more , and read . Each command has its own strengths and weaknesses, and using the appropriate command depends on the user’s preference and the task at hand. It is important to be familiar with these commands to efficiently navigate and manipulate text files in Linux. With this comprehensive guide, you should be well on your way to mastering the command line in Linux.

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Unix Tutorial #3: Reading Text Files¶

The command line is useful for both viewing and manipulating text files. Manipulation means editing text - for example, replacing words in text files, or appending text from the command line to the end of a file (also known as redirection). This is useful for creating scripts, text files containing one or more commands that are run consecutively. In later tutorials, you will use these techniques to automate your analyses, which can save enormous amounts of time.

You can display the contents of a file using the cat command, which stands for concatenate. Let’s say we have a file on our Desktop called myFile.txt, which contains the words one through fifteen (i.e., one, two, three…fifteen), with each number on a separate line. Use the command line to navigate to the Desktop, and then type cat myFile.txt . This will print the contents of the file to your command line. This is the same idea as using the GUI to double-click on the text file to see its contents.

Using the command line and the GUI to read the contents of a text file. On the left is the command line using the cat command, which prints the contents to the Terminal. On the right is the contents of the file displayed after using the mouse to double-click the file.

We refer to the output from this command as stdout, or standard output. The commands that are typed into the Terminal are called stdin, or standard input. This touches on the concept of streams, or the flow of information into and out of the command line, and we will use these ideas to give us more flexibility in manipulating text files. For now, think of stdin as anything you type into the Terminal, and stdout as what is returned if the command is run without any errors. If the command that you type does result in an error - for example, because the command was misspelled or because not enough arguments were provided - the text that is output to the Terminal is called stderr, or standard error.

Illustration of streams in Unix. Whatever is typed into the Terminal is stdin, and, if it runs without error, whatever is output is called stdout. If there is an error, the output is instead called stderr.

The cat command is useful for viewing the contents of smaller files, but if the file contains hundreds of lines of text, it is overwhelming to have everything printed to the Terminal at once. To see only a part of the file, we can use the commands head and tail to see the first few or the last few lines of the file, respectively. Using myFile.txt as an example, typing

Would return the first five lines; whereas typing

Would return the last five lines. Although the default is to return five lines, these commands have an option to display any amount of lines that you choose. For example,

head -10 myFile.txt tail -10 myFile.txt 

Would return the first ten lines and the last ten lines. Try these out yourself, changing the number of lines that are displayed.

Redirection¶

In addition to displaying the results of a command, stdout can be used to move or append the output to a file, a concept known as redirection. For example, if you type

The word “sixteen” goes into the file tmp.txt instead of being written to standard output. Notice that it creates the file tmp.txt even if it doesn’t exist. However, if we try that again with another string - for example,

It will overwrite the file with whatever we printed to standard output. If you want to append standard output to the end of a file without overwriting the other data in the file, use two greater-than signs. For example, type

If you type cat tmp.txt , you will see both seventeen and eighteen.

Although these examples are trivial, redirection is invaluable for quickly editing text files and for writing scripts, which allow you to run analyses for hundreds or thousands of subjects with only a few lines of code.

Video¶

Click here for a video walkthrough of commands for reading text files. This video will also show you how to read help files using the less command and a paging window.

Exercises¶

1. Create a new file called “tmp.txt” and type whatever you want into the file. Use cat to string together both the myFile.txt and tmp.txt files, and redirect the output to create a new file. Print the contents of the new file to stdout.
2. If you have AFNI installed on your machine, use less on the command 3dcalc to find strings matching “Example.” Now try it using the less command with an option to ignore whether the letters in the string are upper case or lower case. Hint: To find this option, search for the string “case” in the man file for less . (If you have FSL installed instead of AFNI, try the same exercise with the command fslmerge .)
3. Unix has a built-in command called sort which will sort text numerically or alphabetically. What happens when you use myFile.txt as an argument for sort ? What about typing this command:

In your own words, explain the difference between the two methods.

© Copyright 2019, Andy Jahn Revision cb9a0b41 .

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