Let’s consider a case where we have two directories, say, d1 and d2 and both these directories contain some files, which may be the same or different. Now we want to make use of the sed command to replace a particular text that might be present in some of the files in either the d1 directory or the d2 directory.In order to do that, we must be familiar with the sed commands, as the sed commands can be used to solve the above problem.Let’s first explore the sed command, which is short for stream editor. This command is used to ... Read More

In order to be able to grep a string that has a dot inside it, we must first understand what a grep command is and how to use it on Linux.The grep command in Linux is used to filter searches in a file for a particular pattern of characters. It is one of the most used Linux utility commands to display the lines that contain the pattern that we are trying to search.Normally, the pattern that we are trying to search in the file is referred to as the regular expression.Syntaxgrep [options] pattern [files]While there are plenty of different options available ... Read More

You might have been in a scenario where you are using a Linux as your main operating system and then you try to create or edit a file and the Linux terminal responds with something like “Permission deny” error. In typical sense, such an error is related to insufficient permissions that your current user is having and can be solved by setting the correct file permissions or changing the owner.In Linux, the files are controlled through the file permissions, ownership and attributes, which in turn makes sure that only authorized users and processes can access files and directories.Before understanding how ... Read More

Linux find statement is one of the most widely used statements that allows us to walk a file hierarchy. It is used to mostly find a specific file or directories and we can also append different other Linux statements or flags along with it to enhance or do a complex operation.Let’s explore an example of a find statement to understand it better.In the Linux code shown below, I am trying to search for a file inside my Downloads folder, and for that I am making use of the find statementfind sample.shOutputsample.shNotice that if the find command is able to locate ... Read More

Unzip is the Linux command utility that we will use to unzip all zipped files present in a Linux directory.By default, the unzip utility is not present on most of the Linux distributions and we can install the same with the help of the commands mentioned below.For Ubuntu and Debiansudo apt install unzipFor CentOS and Fedorasudo yum install unzipSyntaxunzip file.zipIn the above syntax we just need to replace the file.zip with the file that we want to unzip.Consider a case where I have a directory named direct1 that looks something like this −immukul@192 direct1 % ls -ltr total 5216 -rwxrwxrwx ... Read More

In order to test a crontab job we first need to explore and understand what a crontab job is.A crontab job is nothing but a list of commands that we can run during a cron job. A cron job is a utility that schedules automatic execution of commands at specific times.We can start a cron job with the help of bash script by following the commands shown below −crontab -eThis will open a file which you can edit, insert the cron job shell script in the above file and then close that file.Just insert the code shown below in the ... Read More

The grep command in Linux is used to filter searches in a file for a particular pattern of characters. It is one of the most used Linux utility commands to display the lines that contain the pattern that we are trying to search.Normally, the pattern that we are trying to search in the file is referred to as the regular expression.Syntaxgrep [options] pattern [files]While there are plenty of different options available to us, some of the most used are −-c : It lists only a count of the lines that match a pattern -h : displays the matched lines only. ... Read More

An Environment variable is a dynamic-named value. Generally, these are variables are exported in a single terminal using a command shown belowexport $SOMEVARIABLE=valueor they are stored inside the bash files, so that they remain available in all the terminals once the file is sourced. If we want to change an environment variable we can simply change the above command’s value field and then source the file, but if we want to do that with the help of the sed command then we need to know a little bit about the sed command.Let’s explore the sed command, which is short for ... Read More

In order to be able to sort the contents of a file in Linux, we must first be aware of the sort command that Linux provides us with.The sort command is mainly used to sort the contents of a file. It arranges the records in a particular manner. By default, these records are sorted considering the fact that they are ASCII based values.Few key points to remember about the sort command are −SORT command does the sorting from one line to another, one line at a time.It prints the contents of the file when used on a file, in the ... Read More

In order to simulate the packages that got delayed or dropped we can make use of the netem which provides us with a network emulation functionality that is helpful in testing protocols.The way netem works is that it tests the protocols by emulating the properties of wide area networks.There are different versions of netem and the current stable version allows us to emulate variable delay, loss, re-ordering and duplication of packets.There are two ways in which we can use the network emulator, the first is the most basic one where we can enable the netem kernel component by following the ... Read More