1. To rename a file in ubuntu

Syntax : mv filename1 filename2

e.g. If we need to change a filename to indexold from index.php

        mv index.php indexold

2. To rename a folder

    Syntax : mv foldername1 foldername2

    e.g To rename letsknowit folder to letsknowitnew

          mv letsknowit/ letsknowitnew

3. Copy a file to other location (keep the original file and make a duplicate of it)

    Syntax: cp filename targetpath/

   e.g. Copy a file letsknowit.txt to var/log folder

       cp letsknowit.txt /var/log/

4. To copy a file from a remote server to a our local machine

 Syntax : scp username@hostname:/filetodownlod /localpath

 e.g. If we want to download payment.log file from var/logs folder to out logs folder

        scp root@11.1.1.1:var/log/payment.log /var/www/html/logs

5. To clear the contents of a file

 Syntax :  > filename
 
e.g If we want to clear the content of letsknowit.log

  > letsknowit.log

6. To delete the files have some specific extension

 Syntax :  rm *.extension
 
e.g If we want to delete all the files have a .gz extension

  rm *.gz