Gain insights into the power of the command line. Learn about Linux BASH through theoretical and practical exercises, mastering essential concepts and commands for efficient programming.

Ever wondered why command line is still in use even when there are hundreds of human-friendly GUI’s and tools available? Everyone in the programmer's world would agree on one thing: Command Line is far more powerful than any GUI. It provides a richer experience in terms of speed and expressiveness.

For beginners, it might be hard to appreciate its beauty and a little challenging to shift from an interactive interface to a blank box with just a “$” sign showing that keeps prompting the user to enter complex commands if you want to get something done. This is why we felt the need to build a course which could help the user overcome his/her fear of using the terminal (we have all been there).

The objective of this course is to help you get a strong grip over Linux, mainly focusing on BASH. You will be covering both, the theoretical and practical sides. First, you will learn a bunch of concepts necessary to understand things and then study some nifty commands to get useful things done out of them.

Bash for Programmers

|  **Command**   |  **Definition**   |  **Syntax**   |   **Example**  |
| --- | --- | --- | --- |
|bc|`bc` is an arbitrary-precision language for performing math calculations.|`bc [ -hlwsqv ] [long-options] [file]`|To assign the variable `var` a value of **5** and display in on the console: `echo "var=5;var" | bc`|
|chdir (change directory)|`chdir` is the system command for changing the current working directory.|`chdir direectory_name`|To change directory to "/home/etc/ww": `chdir /home/etc/ww`|
|  df (disk free)   |  It reports the amount of space used and available on currently mounted filesystems.| `df [option(s)] [device(s)]`    |  To get information only for the root directory: `df /`   |
|  du (disk usage)  | It shows the sizes of directories and files.    |  `du [options] [directories and/or files]`  |  This will show the sizes of all directories that are in *dir2* that resides in *dir1*: du dir1/dir2|
|  file   |  This command classifies filesystem objects.   |  `file [option(s)] object_name(s)`  | Information about a file named "file1.txt" can be obtained by: `file file1.txt`    |
|   free  |  It provides information about unused and used memory and swap space. | `free [options]` | To show all of the data in megabytes: `free -m`    |
|gzip|It is used to compress or decompress files.|`gzip [options] [suffix] [filename]`| To decompress a file "file.gz": `gzip -d file.gz`|
|   halt  |  This command instructs the hardware to stop all CPU functions.   |  `halt [option]`   |  `sudo halt`   |
|  hostname  |  Shows or sets a computer's host name and domain name.   |  `hostname [options] [new_host_name]`   |  To change the hostname to "host2": `hostname host2`   |
|   kdesu  |  It opens KDE su, the graphical front end for the su command.  | `kdesu [-u username] [options] command`    |  To allow Nautilus (the official file manager for the GNOME desktop) to be run as root during an ordinary user session: `kdesu -c nautilus` |
|  killall  | It terminates all processes associated with programs whose names are provided to it as arguments.    | `killall [options] program_name(s)`| To abruptly terminate nautilus (which is the official file manager for the GNOME desktop): `killall nautilus`    |
|less|`less` is the more powerful version of `more`. It allows backward movement in the file as well as forward movement. Also, `less` does not have to read the entire input file before starting, so with large input files it starts up faster than text editors like *vi*. |`less <file name>`|`less /var/log/file`|
|  mkfs (make filesystem)  |  It creates a filesystem on a disk or on a partition thereof.   |  `mkfs [ -V ] [ -t fstype ] [ fs-options ] filesys [ blocks ]`   | This would create an ext2 filesystem on a formatted floppy disk that has been inserted into the first floppy drive: `mkfs /dev/fd0`    |
|more|`more` shows information one page at a time.|`more [filename]`|To view the directory listing of a file, one page at a time: `more file.txt`|
|  mv  |  It renames and moves files and directories.| `mv [options] argument(s)`    |  To rename "file1.txt" to "file2.txt": mv file1.txt file2.txt   |
|  pstree  | It displays the processes on the system in the form of a tree diagram.    |  `pstree [options] [pid or username]`   |  To show only those branches that have been initiated by a user with a username *runner*: `pstree runner`  |
|  reboot   |  It restarts a computer without having to turn the power off and back on.   |  `reboot [option]`   |  `reboot`   |
|  rsync  | It is a fast copying too.    | `rsync [options] src [dest]`    |  `rsync -v /var/lib/rpm/file /root/temp/file`   |
|  runlevel  | It reports the current and previous runlevels.    |  `runlevel [utmp]`  |  It is usually used without any options: `runlevel`   |
|  sed (stream editor)  |  It allows you to filter and transform text.   |  `sed options [script] [Iimputfile]`   | To replace all instances of "cat" with "dog" in 'file.txt' `sed 's/cat/dog/g' file.txt`   |
|  shred  | It destroys files.    |  `shred [option(s)] file(s)_or_devices(s)`   | To securely destroy "file1.txt" and "file2.txt": `shred file1.txt file2.txt`    |
|  shutdown   | This command allows you to shutdown a Windows XP, Vista, 7, 8, or 10 computer from the command line, as well as perform additional functions that are not available through Windows.    | `shutdown [option]… TIME [MESSAGE]`    |  `sudo shutdown 5` ; it will shut down system after 5 minutes.  |
|  spell  | This command checks spellings.    | `spell [options] [file_name(s)]`    |  To spell-chek "file.txt" : `spell file.txt`  |
|  strings  | It returns each string of printable characters in files.   | `strings [options] file_name(s)`    |  To display all strings in file1.txt that consist of at least 3 characters: `strings -n 3 file1`  |
|  su (substitute user)  | It changes a login session's owner without the owner having to first log out of that session.  |  `su [options] [commands] [-] [username]`  |  To change the user of current login session to *anna*: `su anna`  |
|tar|This command is used to archive files in tar format. We can also used this command to convert, maintain, and extract tar files.|`tar [option(s)] [archive] [file_name(s)]`|`tar -cf my_files.tar file_1 file_2 file_3`|
|  tr  | It translates or deletes characters.    | `tr [options] set1 [set2]`    |  To replace every instance of text-typed *a* with *b*: `tr a b` |
|  unalias   |  It removes entries from the current user's list of aliases.   |  `unalias [-a] [alias_name(s)]`   | If a user had an alias named p for the `pwd` (i.e., present working directory) command, such alias could be removed with: `unalias p`    |
|  uptime  | It shows the current time, how long the system has been running since it was booted up, how many user sessions are currently open and the load averages.    |  `uptime [option]`   |  `uptime`  |
|  vim   |  It is used for editing any kind of text and is especially suited for editing computer programs.   |  `vim [options] [filelist]`   |  To edit a single file: `vim file.txt`   |
|  w   |  `w` shows who is logged into the system and what they are doing.   |  `w [options] [username1, username2, . . .]`   |  `w` ; running this command with no arguments shows the list of users along with their ongoing processes.   |
|  whatis   |  It gives very brief descriptions of command line programs and other topics related to Linux and other Unix-like operating systems.   |  `whatis keyword(s)`  |  `whatis sudo`   |
|  wc (word count)   |  This command counts the number of lines, words and characters that are contained in text.|  `wc [options] [file_name(s)]`   |  `wc file1 file2`   |
|  whereis   | It locates the program, source code, and manual page for a command.|  `whereis program_name(s)`   |  `whereis ls`   |

Here's a concise cheatsheet for some miscellaneous commands used in Linux.

Introduction to Bash

Navigation Commands

File Manipulation Commands

Permission Commands

Filtering & Searching Commands

System & Process Commands

Variables and Environment

An Overview of Commands

Misc. Commands' Cheatsheet