cat filename...where filename... may be one or more files.
cat displays the content of filename... on the standard output. If more than one file is used, they are displayed one after the other creating a larger file.
Output redirection may be used to copy the contents of files into another file. An example is
cat *.c > tot.cprog
This will copy the contents of all files ending with .c, into file tot.cprog. The order of the files within tot.cprog will be alphabetical.
cat can be used to append one file to another:
cat file2 >> file1will append file2 to file1.