$1.$ What are the BASH shell file descriptors?

$2.$ What does the following command do$?$

ls $$l $/$etc $>$ goodoutput

$3.$ What does the command ls ~ $1>$ listout? What is the output of ls ~ $>$listout$2?$ Is there a difference between the two output files?

$4.$ What does this command do$?$ ls $$l $/$etc$/$hosts $/$etc$/$h $2>$badoutput

$5.$ What command will redirect a file: $$names$$ as input to the sort utility? And the output to file: $$sortednames$$

$6.$ How can you append the contents of file $$morenames$$ to the file $$names$?$

$7.$ How can you send the standard output of a command to another command?

$8.$ What is the difference between redirection and piping?

$9.$ What is a shell variable?