cat commands

 cat: cat command to write the contents of a file to the screen.

To read the contents of the file, type

cat list1

Then type a few words on the keyboard and press the [Return] key.

Finally hold the [Ctrl] key down and press [d] (written as ^D for short) to end the input.

Concat two files 

cat list1 list2 > biglist

What this is doing is reading the contents of list1 and list2 in turn, then outputing the text to the file biglist