Often it is a requirement to read each of the line from a file using a bash script. There are various approaches to read the lines form a file. In the below example we have first described how to create a sample file and then run a script reading that sample file.Create a file to Read# Open vi Editor vi a_file.txt # Input the below lines Monday Tuesday Wednesday Thursday Friday Saturday Sunday # cat the file cat a_file.txtRunning the above code gives us the following result −Monday Tuesday Wednesday Thursday Friday Saturday SundayUsing Do-WhileIn this approach we use a ... Read More

When we transfer files between Windows and Unix systems, often we come across with issue relating to the end of line character. This is because the EOL character in windows is not recognized as a EOL character in Unix. SO to fix this issue when a file is transferred from Windows to Unix we need to follow one of the below methods.Using dos2unixThe dos2unix command is used to convert the EOL character of windows platform to Unix platform. Most of the Unix system comes with this command pre-installed. Below we see how we can convert the file itself or save ... Read More

The wc command also known as word count command is a fundamental command any Linux user should be aware of. It is mostly used with the l switch to do a line count, but it can actually give count of multiple things with various arguments supplied to it. Below is a list of what are those possible arguments. The we will see examples on each of them.Sr.NoCommandUsage1wc -cDisplay number of bytes2wc -mDisplay number of characters3wc -wDisplay number of words4wc -lDisplay number of lines5wc -LDisplay length of longest lineLets consider the below file for our examples.ubuntu@ubuntu:~$ cat inspire.txt Mastering anything needs ... Read More

Removing directories is a regular process for anyone working on Unix systems.But sometimes we also need to find the directories first and then decide to delete it. One hurdle in deleting the files is to do a recursive deleting because by default Unix systems do not allow deleting of a directory if it is not empty. So in this article we will see how to find and remove directories recursively.Using find and execThe below command first searches for the required directory using the find command then executes the ‘rm’ command to recursively remove the directory using the recursive option as ... Read More

Re-running commands in the command line is a regular task which all of us go through when working on the Unix systems. In the below article we will see various ways how we can rerun the commands we have already executed this helps save time and it helps reasoning longer commands easily without retyping them.Before we get into how to re-execute previous command let's see how we can look at the list of all the commands. There is a command call history which lists down all the executed command for a specific time period configured by the system. Below is ... Read More

Because of security concerns, the users in a system are required to update their passwords regularly. In this article we will see how we can force an user to change their password when they login to the system next time.List the usersFirst lets have a look at the users available in the system.$ cut -d: -f1 /etc/passwdRunning the above code gives us the following result −mail news uucp proxy www-data backup list … Ubuntu uname1Check user DetailsNext we check the settings for users current password system configuration.$ sudo chage -l uname1 [sudo] password for ubuntu:Running the above code gives us ... Read More

For the sysadmins, it is routine to monitor user details like who are active and who are not, who logged in in last 2 days, which users belong to a given group etc etc. To help these requirements, Linux provides below list of commands which can be used to gather various types of information about the users.id CommandIt gives the id details of users including the group id along with the secondary group IDs and names of a user choosen by the system. But you also ask for a specific user’sdeatils by giving the userid value in the command.ubuntu@ubuntu:~$ id ... Read More

For purpose of security, cyber-crime investigation, government compliance or just for curiosity we might ned to track the geographical location of a Linux server in the internet or at least the location of the server which diverts the internet traffic to the server we are interested in. It involves getting the I.P address of the server and using some third party services offered in the web, to map that I.P address to get the location. In this article we will see the steps to achieve that.Step 1 − Install curl jqThe curl package will make the http requests to the ... Read More

Usually a continuously growing files, needs to be emptied from time to time to accept the latest data from the next operation. There are various mechanisms to empty the file. We will see them one by one below. The common approach is the overwrite the target file by using > sign which should come from a source which is empty./dev/nullThis is a common method where we output empty result and then redirect that result to the target file.# Original file size $ls-lt -rw-rw-r-- 1 ubuntu ubuntu 2925 Jan 1 08:39 ref_file.txt # Redirect the output from /dev/null $ cat /dev/null ... Read More

We can download any required file form the web using the linux terminal. But many times it is found that the downloaded file is a zipped file which is in tar format. In this article we will see how to download and extract the file in a single command.Using wget and tarThe wget command downloads the data form the given URL while the tar command does the extraction of the tar.gz files.$ wget -c https://www.metoffice.gov.uk/hadobs/hadisd/v300_2018f/data/WMO_200000-249999.tar.gz -O - | sudo tar -xzRunning the above code gives us the following result:--2020-01-01 07:25:18-- https://www.metoffice.gov.uk/hadobs/hadisd/v300_2018f/data/WMO_200000-249999.tar.gz Resolving www.metoffice.gov.uk (www.metoffice.gov.uk)... 104.80.55.230 Connecting to www.metoffice.gov.uk (www.metoffice.gov.uk)|104.80.55.230|:443... connected. ... Read More