cat

Print and concatenate files. More information: https://manned.org/cat.1posix.

cat path/to/file

cat path/to/file1 path/to/file2 ... > path/to/output_file

cat path/to/file1 path/to/file2 ... >> path/to/output_file

cat -u /dev/tty12 > /dev/tty13

cat - > path/to/file