This tutorial is the second part of the introduction to Linux command-line. In the first chapter I tried to make a brief introduction to the shell and the basic ways of moving around. Here I will talk about several useful commands, which may be needed on a day to day basis if you're working with the shell.

Working with Files and Directories

Creating Directories

The command to create new directories (also called folders) is mkdir. For example, to create a directory called books inside your home directory, you would issue the following command:

Renaming Files

In Linux, renaming a file is done via the mv command, which stands for 'move'. The general format of the command is: So, if for example you would like to rename the directory created previously, books to mybooks2, you would issue the following command:

Copying Files

The command for copying files and directories is cp. For example, to copy the file /etc/network/interfaces to you home directory you could write the following: Make sure to replace USER with your username. Or, if we keep in mind that ~ is automatically expanded into the home directory of the current user: And if your current working directory is already your home directory (e.g. /home/USER): The character . expands into the current directory. See the first chapter to see more details on this. You could even use environment variables, which expand into a certain string. In the following example, the variable $HOME holds the path to your home directory: You can copy more than one file at a time, the last argument being the directory where you want the files to be copied: This command will copy myfile1, myfile2 and myfile3 from the current working directory into the books folder, located inside your home path.

Copying Directories

Directories can be copied in the same fashion as files, only this time we will use the -r switch. This tells the cp command to copy directories recursively, meaning all the sub-folders and files of the specified directory. This command will copy the Documents folder from the current directory inside the books directory located in your home path.

Creating Files

To create empty files, you can use the touch command. In a later chapter I will discuss on how to create and edit or modify text files with various editors.

Removing Files

To delete a file, you would use the rm command: To delete a directory, you will also need the -r switch:

Adding Users

Adding a New User

The command is adduser which is a user-friendly wrapper for the useradd command. More on administrating users and groups in a later chapter.

Other Commands

View the Current Date and Time

Use the date command for displaying the date and time: In addition, you can use format specifiers to display the date and time differently. For example, you could use the %Y (year), %b (abbreviated month name), %d (number of the day, two digits), %H (hour, 24-hour format), %M (minute), %S (second): To change the date and time, use the --set switch: The above command will change the hour and minute to 16:56.

Calendar

The cal command will display an ASCII calendar of the current month, and will highlight the current day:

Show Your Username

The whoami command will print the username currently logged in. Additionally, you can use the echo $USER command, which will use the $USER environment variable to echo (print) its value:

Print System Information

For this we will use the uname command with the -a switch, to show all the information available: This shows the kernel version, the date and processor architecture. Except for uname, there are two other commands which print hardware information, lspci which prints all the PCI devices, and inxi, which is a script usually available on Linux Mint systems. inxi displays extended information about the CPU, kernel, memory, hard-disk space and so on.

Show Uptime

The uptime command is used to print for how long the system has been running:

Print Text

The echo command is used to output text: You can use the echo -e command to interpret special characters (like in C): Here we used a horizontal tab (\t), and two newlines at the end (\n). Notice how the ! character is escaped too.

Searching for Commands

Commands and programs usually reside inside the /bin, /sbin and /usr/bin directories. To search for a command in such standard locations, use whereis: To search for a command in all the possible locations in your $PATH, use which:

Show File Types

Use the type command for this:

Getting Help

Usually commands have a manual page, so for any command you could use man COMMAND to read a detailed help about what it does and how to use it. The manual page lists all the parameters you can pass to the command. Once you've opened a manual page, you can navigate through it via the arrows, Ctrl+P or Ctrl+N to read the previous and respectively, next line, or Q to quit and close the manual page and return to the shell.

Commands usually have a -h or --help parameter, which will display a short description on what the command does and a compact list of parameters that it takes.

More on getting help in a following chapter.

By Craciun Dan on October 02, 2014 | Updated: October 02, 2014 r1