What do the following commands do.

a. cat 1> letter 2> save 0< memo

b. cat 2> save 0< memo 1> letter

c. cat 1> letter 0< memo 2>&1

d. cat 0< memo | sort 1> letter 2> /dev/null

a. The cat command reads the memo file and puts it in a file called letter. If the memo file does not exist, the error message is stored in the save file.
b. Same as for the command in part (a).
c. The cat command reads the memo file and puts it in a file called letter. If the memo file does not exist, the error message is sent to standard error (the display screen).
d. The cat command reads the memo file and sends it to the sort command, who sorts it and puts the sorted version in a file called letter. If the memo file does not exist, the error message is sent to standard error (the display screen). If the sort command fails, the error message goes to /dev/null, never to be seen.