How we can copy for example 10 bytes of '7' to a file?
How can I generate those 10 bytes of 7?
For example for n bytes of zero I'm doing dd if=/dev/zero of=myFile bs=1 count=10.
Answer
You can send the zeros to stdout and translate them to 7, or what ever you like.
dd if=/dev/zero bs=1 count=10 | tr "\0" "\7" > file.bin