Mostly all command gives output on screen or take input from keyboard, but in
Linux it's possible to send output to file or to read input from file. For e.g. $ ls
command gives output to screen; to send output to file of ls give command , $ ls
> filename. It means put output of ls command to filename. There are three main
redirection symbols >,>>,<
(1) > Redirector Symbol
Syntax: Linux-command > filename
To output Linux-commands result to file. Note that If file already exist, it will be
overwritten else new file is created. For e.g. To send output of ls command give
$ ls > myfiles
Now if 'myfiles' file exist in your current directory it will be overwritten without any
type of warning. (What if I want to send output to file, which is already exist and
want to keep information of that file without loosing previous information/data?,
For this Read next redirector)
(2) >> Redirector Symbol
Syntax: Linux-command >> filename
To output Linux-commands result to END of file. Note that If file exist , it will be
opened and new information / data will be written to END of file, without losing
previous information/data, And if file is not exist, then new file is created. For e.g.
To send output of date command to already exist file give
$ date >> myfiles
(3) < Redirector Symbol
Syntax: Linux-command < filename
To take input to Linux-command from file instead of key-board. For e.g. To take
input for cat command give
$ cat < myfiles
Pips
A pipe is a way to connect the output of one program to the input of another
program without any temporary file.
Linux Shell Script Tutorial