cat file ...
The cat command takes a list of file names for its arguments.
It outputs the contents of those files directly to the standard output, which, by default, is directed to the screen.

• Write the content of a file:
  $ cat file1 Hello file1
  You can use the option -n to print the line number:
  $ cat -n file1 1 Hello 2 3 file1
  
• Write the content of multiple files:
  $ cat file1 file2 file3
  
• Write the content of multiple files one by one (enter EOF character ('^D') for each file):
  $ cat file1 - file2 - file3

The following options can be used:
-n |Number the output lines, starting at 1. -b |Number the non-blank output lines, starting at 1. -v |Display non-printing characters so they are visible. |Control characters print as "^X" for control-X; the delete character (octal 0177) prints as "^?". |Non-ASCII characters (with the high bit set) are printed as "M-" (for meta) followed by the character for the low 7 bits.