EOF in shell scripts and file redirection

<<eof
Content
EOF
You can replace EOF with something else (the decomposition character)
It means to pass the content as standard input to the program.

Here is a brief look at the use of <<. When the shell sees <<, it will know that the next word is a demarcation
Character. The content after the delimiter is treated as input until the shell sees the delimiter again (on a separate line). This one
The delimiter can be any string that you define.

Frequently used file redirection:

Command > FileName redirect standard output to a new file
Command >> filename REDIRECT standard output to a file (append)
Command 1 > FileName REDIRECT standard output to a file
Command > FileName 2 >&1 redirect standard output and standard error to a file
Command 2 >filename redirect the standard error to a file
Command 2 >> filename redirects a standard error to a file (append)
Command >> filename 2 >&1 redirect standard output and standard error to a file (append)
The command < filename > filename2 command commands the filename file as the standard input,
filename2 file as standard output
Command < filename commands with filename file as standard input
Command << delimiter is read from the standard output until the delimiter delimiter is encountered
Command <&m the file descriptor m as standard output
Command >&m redirect the standard output to the file descriptor m
Command <&-to turn off standard input

Note: <<delimiter as the delimiter is absolutely not mixed with <<filename, because the latter does not exist at all ...