File Prompting Commands in linux?

head    :   used to view first 10 lines of a file
   
    syntax :   head <filename>
    ex: head /etc/passwd

To view 4 lines of a file
  
    head -n <no of lines> <filename>
    ex: head -4 /etc/passwd

Tail : is used to view last ten lines of a file

    syntax: tail <filename>
    ex: tail /etc/passwd

To view last 10 lines of a file
  
    tail -10 /etc/passwd

more : used to see the content pagewise but we cannot scroll up

    syntax: more < file name>
    ex: more /etc/passwd

less: used to see the content pagewise we can scroll up&down

  syntax: less <filename>
  ex: less /etc/passwd

date: used to view current date&time

to change date

date  <mm-dd-hr-min-year>

ex: date 120111452013
  it means 12th month 01 date 11:45 11 hours 45 minutes 2013 year
or
  date -s <content>
  date -s "wed june 20 20:46:51 IST 2013"

cal : cal is used to view present months calender

cal to view a particular month,particular years calender

 cal <Month> <year>

cal 5 1986 -------------> to view may 1986 calender
cal 2050 ----------------> to view entire 2050 year calender 
    |                 --------> this symbol is called as pipe it is used to link conmmands

  ex: ls | grep pot

grep : is used to skip something specially from the output
here in example from output of ls we are grepping pot

ll | grep "^d" ---------> here from the out put of ll we are greping only directories
mkdir <directory name> -----> to create a directory
ex: mkdir mahesh

To create multiple directories :
mkdir <dir1> <dir2> <dir3>
ex: mkdir d1  d2  d3

To create nested directory
mkdir -p <dir1/dir2/dir3>
mkdir -p world/asia/india/ap/vskp/mahesh

To change the directory
 cd < path of directory>

To change directory one level back
 cd ..

To change directory two levels back
 cd ../..

Removing a file or directory
to remove a file
rm <filename>
to remove an empty directory 
 rmdir <dir-name>

To remove directory recursively & forcefully
rm -rf -> to delete directory with out asking yes or no

copying a file
cp <sorce> <destination> -----> to copy a file
ex: cp file1 /etc/
cp -rf <source > <destination> ---> to copy entire directory along with subdirectories & files
ex: cp -rf mahesh /opt/
cp -a <source> <destination> -----> to copy a file or directory along with permissions
ex: cp -a Server /var/ftp/pub

To move a file or directory
mv < source> <destination>
mv mahesh /opt/users/

To rename a file or directory
mv <oldname> <newname>

To create chain commands
In linux we can execute "n" number of commands at a single command line
syntax: command1;command2;command3;

ex: date;cal2013;date 120111452013;mkdir mahesh;cd mahesh;cd