CAT(1) General Commands Manual CAT(1)
cat - catenate and print
cat [ -u ] file ...
Cat reads each file in sequence and writes it on the standard output.
prints the file and
cat file1 file2 >file3
concatenates the first two files and places the result on the third.
If no file is given, or if the argument `-' is encountered, cat reads
from the standard input. Output is buffered in 512-byte blocks unless
the standard output is a terminal or the -u option is present.
Beware of `cat a b >a' and `cat a b >b', which destroy input files
before reading them.