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To negate an "if" condition in a Bash script in Linux, you can use the "!" operator. For example, if you have an "if" statement that checks if a variable "x" is equal to 5, you can negate that condition by using "if [ ! $x -eq 5 ]" instead. This will run the commands inside the "if" block if the condition is not true (i.e. if "x" is not equal to 5). Integer Comparison In Bash, you can use the following operators to compare integers − eq (equal to) ne (not equal to) gt (greater than) ge (greater ... Read More
The /etc/hosts file is a simple text file used to map hostnames to IP addresses. It is used to resolve hostnames to IP addresses, bypassing the need for a DNS server. Each line in the file represents a single mapping, with the IP address followed by one or more hostnames separated by spaces. You can map hostnames with ports by specifying the hostname followed by the port number, separated by a colon. For example, to map the hostname "example.com" to the IP address "192.168.0.1" on port 80, you would add the following line to the /etc/hosts file − 192.168.0.1 example.com:80 ... Read More
You can use the "mount" command to check if a directory is mounted on a Linux system. For example, to check if the directory "/mnt/data" is mounted, you can run − mount | grep "/mnt/data" If the directory is mounted, the command will return information about the mount point, including the file system type and the device it is mounted on. If the directory is not mounted, the command will return nothing. You can also check if a directory is a mount point using the findmnt command. findmnt -T /mnt/data This command will show all the mountpoints for ... Read More
cd stands for "change directory" and is used to navigate the file system on a Linux computer. When used with a specific directory path as an argument, cd will change the current working directory to that location. For example, the command cd /home/user/documents will change the current working directory to the "documents" folder located within the "user" folder in the root directory. If you use cd command without any argument it will take you to your home directory. The Meaning of – With cd The "-" (dash) symbol is a shortcut that can be used with the cd command to ... Read More
In Linux, a pipe is a mechanism that allows the output of one command to be used as the input for another command. Pipes allow for powerful command line operations by allowing the output of one command to be used as input for another command. Pipes Pipes are a feature in Linux and other Unix-like operating systems that allow the output of one command to be passed as input to another command. They are represented by the "|" symbol, and are often used to chain multiple commands together to perform complex tasks. For example, the command "ls -l | grep ... Read More
You can send emails from the terminal in Linux by using the command line tool called "mail." This tool is typically pre-installed on most Linux distributions. To send an email, you would use the syntax − echo "message body" | mail -s "subject" recipient@email.com You can also include attachments by using the -a option and specifying the path to the file you want to attach. echo "message body" | mail -s "subject" -a /path/to/attachment recipient@email.com You can also use other command line mail clients such as mutt, mailx, etc. Architecture of an Email System An email system consists ... Read More
To read the source code of shell commands on Linux, you can use the command line utility cat or less to view the file. You can also use a text editor such as vi, nano, or emacs to open and edit the code. For example, to view the source code of the ls command, you can use the command − cat /bin/ls If you want to view the source code of a command that is installed from a package manager, you can use package manager command to find the location of the source code. For example, on a Debian-based ... Read More
To search for a specific pattern within a specific file type using the grep command in Linux, you can use the -r option to search recursively through a directory and the -E option to specify the file extension. For example, to search for the word "example" within all text files in the directory "test", you would use the command − grep -r -E 'example' --include='*.txt' test/ This command searches recursively through the "test" directory and its subdirectories, looking for files that have the ".txt" extension and contain the word "example". You can also use find command with -type and ... Read More
Introduction In Linux, hidden files, also known as dotfiles, are files whose names begin with a dot (.) character. These files are often used to store configuration data or other important information that should not be changed or deleted by the user. If you have a directory with a large number of hidden files and you want to move them all to the root directory, there are several ways to do this. In this tutorial, we will discuss two methods for moving all files, including hidden files, from a directory to its home directory in Linux: the mv command and ... Read More
Introduction Cron is a utility in Linux that allows users to schedule commands or scripts to run automatically at a specific date and time. However, sometimes it may be necessary to ensure that a cron job does not run more than once at a time. In this article, we will discuss two ways to prevent overlapping cron tasks: using process tracking and using a “.pid” file. Locate running instances by process One way to avoid overlapping a cron task run is to check for the presence of the task's process before running it. This can be done using the pgrep ... Read More