Unix: prepending a file without a dummy-file?

Question

I do not want:

$ cat file > dummy; $ cat header dummy > file

I want similar to the command below but to the beginning, not to the end:

$ cat header >> file

Answer 1

You can't append to the beginning of a file without rewriting the file. The first way you gave is the correct way to do this.

Answer 2

Thanks to right searchterm!

echo "include .headers.java\n$(cat fileObject.java )" > fileObject.java

Then with a file:

echo "$(cat .headers.java)\n\n$(cat fileObject.java )" > fileObject.java

Answer 3

You can't prepend to a file without reading all the contents of the file and writing a new file with your prepended text + contents of the file. Think of a file in Unix as a stream of bytes - it's easy to append to an end of a stream, but there is no easy operation to "rewind" the stream and write to it. Even a seek operation to the beginning of the file will overwrite the beginning of with any data you write.