Linux Input Redirection
The bash shell uses stdin to take input. In input redirection, a file is made input to the command and this redirection is done with the help of '<' sign.
Look at the above snapshot, command "cat < file.txt" has taken 'file.txt' as input and displayed its content.
<< here document
The here document (sometimes also called here-is-document) is a way in which you can enter input until a certain sequence(usually EOF) is typed. The EOF (End Of File) can be typed or can be called by pressing (ctrl + d) keys.
Any word can be used in place of 'EOF' like we have used 'last'.
Look at the above snapshot, in first example, 'file.txt' is ended when we typed 'EOF' and 'last' in second example.
<<< here string
The here string is used to directly pass strings to a command.
Look at the above snapshot, in this example we have used base64 which we'll study later. Command "base64 <<< format.txt" has decoded file 'format.txt' and then by using command 'base64 -d' we got back our file 'format.txt'.