How to write lines in a file, HereDoc (Here Document)

EOF is a delemiter.
A delemiter can be EOF or _end_of_block or any other word.

# write characters in file.txt
  cat > file.txt << EOF
  ...
  ...
  ...
  EOF

# or
  cat << EOF > file.txt
  ...
  ...
  ...
  EOF

# with white spaces or tabs:
  cat > file.txt <<- EOF
  ... ...
   ... ...
    ... ...
  EOF

# with variables:
  TODAY=$(date +%F)
 
  cat << EOF
  # User defined variables
  Today date is = ${TODAY}
  #Environ Variables
  I am running as = ${USER}
  My home dir is = ${HOME}
  I am using ${SHELL} as my shell
  EOF

# Inside Statements and Loops
  #!/bin/bash
 
  if true;
  then
         cat <<- "END"
         Hello
         World
  END
  fi

https://de.wikipedia.org/wiki/Heredoc
https://tldp.org/LDP/abs/html/here-docs.html
https://linuxtldr.com/heredoc/
https://phoenixnap.com/kb/bash-heredoc

https://www.docker.com/blog/introduction-to-heredocs-in-dockerfiles/