It's a collection of some lesser known but useful Linux commands. All are "Swiss army knife" one-liners which every Linux user should know.

1. Useful Linux Commands
-- Deepak Modak

2. bc
An arbitrary precision calculator language

3. cat - concatenate files and print on the standard output
tac - print files in reverse
Eg :
cat filename
tac filename

4. ls - list directory contents
sl - display animations aimed to correct users who
accidentally enter sl instead of ls.
* sl is not a linux command , need to install package

5. file - determine the type of file
stat - display file or file system status
Eg :
file filename
stat filename

6. factor
Print the prime factors of each specified integer
Eg :
factor 18

7. sudo !!
Run the last command as root.
It automatically prepend sudo to the last command entered.

8. cd –
change to the previous working directory

9. man ascii
Quick access to the ascii table.

10. curl ifconfig.me
Print external IP address

11. wget --random-wait -r -p -e robots=off
-U mozilla http://www.example.com
The non-interactive network downloader
It will download all files, including images mozilla as browsers identity .

12. Ctrl-l
Clear the terminal screen

13. du -h –max-depth=1
List the size of all sub folders from the current location I
human readable form
du | sort -nr | less
List of files and folders, sorted in descending order by size.

14. python -m SimpleHTTPServer
Serve current directory tree on port 8000.
http://localhost:8000/

15. # Tag
Hash tags to organize bash history and very good for finding very long commands
Step :
• Just add a hash tag in every command you type at the end,
• Later can search for the hash tag in reverse-i-search (Ctrl + R).
Eg:
$ tar -xzvf filename #untar
Now, just Ctrl + R, and type untar and you get the command!
# in shell means a comment.