Overview We often perform various file operations on our Linux systems. One of the most common operations is to display certain columns from a text document. Here, we’ll cover the different methods for achieving this. Display Single Column Let's create a new folder for our example. The input.txt files contain the output of the ls -l command in the long listing (long) format. $ cat input.txt -rw-r--r-- 1 jarvis jarvis 200M Nov 27 22:04 file1.dat -rw-r--r-- 1 jarvis jarvis 400M Nov 27 22:04 file2.dat -rw-r--r-- 1 jarvis jarvis 500M Nov 27 22:04 file3.dat -rw-r--r-- 1 jarvis jarvis 600M Nov 27 ... Read More

Overview It’s common when working with Linux to want to stop a process from using a specific TCP/IP protocol. For example, you might be running an application that listens for HTTP requests and you don’t want it to listen on port 80 (the standard HTTP port). You could use the netstat command to see what ports are currently being used by processes − $ netstat -lntp | grep :80 tcp6 0 0 :::80 :::* LISTEN 8072/httpd tcp4 0 0 ::ffff:127.0.0.1:80 :::::80 8069/httpd tcp6 0 127.0.0.5:53 :::* LISTEN 903/named udp6 0 0 :::22 :::* LISTEN 4963/sshd We’ll look at how to ... Read More

Overview We know that we can direct the standard output (std out) of a Linux shell script to a file by using the ">" operator at the end of the Linux shell script. Sometimes, we need to redirect to a file which requires root permissions − for example, ‘sudo command > file_requires_root_. If we use the ‘su’ command, we might get an “Access Denied” message even though we’ve used ‘su’. We’ll look at the causes of this problem and see if there are any solutions. Introduction to the Problem A good example would be an explanation of the problem. Let's ... Read More

Overview In this tutorial, we will see how to execute a file using the / (dot slash) command in Linux. This is one of the most commonly used commands in Linux and it’s very easy to use. Let us first understand what does the dot slash mean? What Does Dot Slash Mean In Linux Commands? The dot slash or the forward slash (/), as you may know, is used to separate directories from files. For example: If I have a directory called “/home/user1/Desktop” then when I type ls -l on that directory, it would show me all the contents of ... Read More

Overview Copying files is one of the most common operations performed by using the Linux shell. We usually use the cp (copy) commands for this purpose. We're going to discuss how to recursively move a folder to another location with or without overwriting. Introduction to the Problem We first need to understand what "Copy a folder to another location" means in this problem. A good example can help you understand it better. $ tree -a . ├── src │ ├── .hidden.file │ ├── srcFile.txt │ └── subSrc │ ... Read More

Overview We’ll look at some ways to create a complete Linux path by combining two paths into one. We’ll first look at some basic techniques for accomplishing this. Then, we'll talk about a generic approach that handles some of the special cases that appear when combining paths. Concatenating Strings to Build a Path We'll start by looking at an example where we want to concatenated strings to create a complete path. $ my_home_dir="/home/shubh/baeldung/" Here we assume that the current directory is where we want to clone the Git repo from. We then create a new folder called my_home_dir inside the ... Read More

Overview We’ll look at how the operating systems behave when we delete, move or replace files that have open handles. We’ll first briefly talk about files and inodes. After that, we’ll look at the different scenarios and see which one occurs in each case. Understanding Files and Inodes Files stored on a Linux file system use inode numbers to keep track of their contents. We usually list the contents of a directory by listing its file names (links) and then their corresponding inode numbers (hard links). We can use stat on a file and see which inode it refers to ... Read More

Overview In this article, we will discuss how to solve the unary operator expected error in Linux. This is one of the most common errors that you may encounter while working with Linux. In this post, we will see how to fix it and what are the possible causes for this error. What Is Unary Operator Expected? The unary operator expects is a type of syntax error that occurs when an expression has only one operand. For example − int x 5; //error - unary operator expected The above code snippet shows an error because there is no binary operation ... Read More

Overview The Linux terminal is an important tool for any user of the operating system, and it's often used to perform various tasks such as viewing log files or running commands. However, sometimes you may need to clear a screen on your computer so that you can see more than one thing at once. In this article we'll look at how to clear a screen in Linux. It’ll be helpful if we clear the command prompt window so that we can see more clearly what we're doing. We’ll discuss the different ways to accomplish this. Using the clear Command You ... Read More

Overview We sometimes need to determine how large or small a particular text document is. For example, if we're trying to figure out how long a certain email message is, we might use the number of lines in that message to help us estimate its size. Linux has several different methods for determining the length of a text document. We’ll take a closer peek at some of the most common ways of calculating the number of lines in a specific file. Setup For this quick tutorial, we’ll be using a text file called “programing.txt” which has some of the most ... Read More