Print and concatenate files. More information: https://www.gnu.org/software/coreutils/cat.
stdout
: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
stdin
to a file:cat - > path/to/file
cat -n path/to/file
M-
prefix if non-ASCII):cat -v -t -e path/to/file