Open a File for reading and associate with Standard Input (STDIN)

< file

Use the current input stream as Standard Input for the program until “token” is seen. This is used in scripting:

<< token

Open a file for writing and truncate it and associate it with Standard Output:

file

Open a file for writing and seek to the end and associate it with Standard Output.It is used to append text to a file using a redirection operator.

file

Redirect FD n to the same place as FD m :

n>&m

Eg :

2>&1

This means send STDERR to the same place that STDOUT is going to.