Cat writes data

1.cat can append content to a file with two >>

Cat >>oldboy.txt<<eof

>1

>2

>eof

The data in the middle of the EOF is added to the file. EOF can also be converted to other characters, but the two must be the same.

The EOF must be the same.

2.cat is more than just viewing, it can also be written to:

Cat >1.txt

Cat >1.txt (enter something to write CTRL + C or ctrl+d stop)

> is an output redirect,< is an input redirect

Reverse flow of data < and <<

Cat writes data