0 - stdin
1 - stdout
2 - stderr

/dev/null - discards all data written to it

{cmd; cmd; cmd} [any operator] foo.txt - chain multiple commands output to file 

cmd > foo.txt - stdout to file (overwrite)
cmd 2> foo.txt - stderr to file (overwrite)
cmd >> foo.txt - stdout to file (append)
cmd &> foo.txt - stdout and stderr to file (overwrite)
cmd &>> foo.txt - stdout and stderr to file (overwrite)
cmd > foo.txt 2>&1 - stdout and stderr to file (overwrite)
cmd < foo.txt - file contents to stdin
cmd <> foo.txt - open file for both reading and writing
cmd1 | cmd2 - stdout from cmd1 to stdin of cmd2
cmd1 |& cmd2 - stdout and stderr from cmd1 to stdin of cmd2