I was reading some documentation and came across this block of bash code:
$ sudo tee /etc/yum.repos.d/docker.repo <<-EOF [dockerrepo] name=Docker Repository baseurl=https://yum.dockerproject.org/repo/main/centos/7 enabled=1 gpgcheck=1 gpgkey=https://yum.dockerproject.org/gpg EOF
It is so intriguing that, first it is using the tee command which I don’t use it in my daily life, second, it has that weird “<<” that I have never seen!
read from standard input and write to standard output and files
As you can tell, after I entered the command “tee output.txt”, it started waiting for my input, when I typed in “line1”, hit enter, it “tee” out the line1 back to the standard input and so does line 2. Then I hit Ctrl+C to stop the input. Then all my previous inputs have been captured and “tee”ed out to the output.txt.
<< Here document
Someone pointed me to this documentation and I realized there is a professional name assigned to this double smaller than symbol called “Here document”, in one sentence, it will use IO redirection to feed a list of commands(stdin) to a command, including interactive ones.
eof is simply a convention for indicate the begining and ending, you can use any character or string you want.