Before a command is executed, its input and output may be redirected using a special notation interpreted
by the shell. Redirection may also be used to open and close files for the current shell execution
environment. The following redirection operators may precede or appear anywhere within a simple command
or may follow a command. Redirections are processed in the order they appear, from left to right.
Appending Redirected Output
Redirection of output in this fashion causes the file whose name results from the expansion of word to be
opened for appending on file descriptor n, or the standard output (file descriptor 1) if n is not
specified. If the file does not exist it is created.
The general format for appending output is:
AND and OR lists are sequences of one of more pipelines separated by the && and || control operators,
respectively. AND and OR lists are executed with left associativity. An AND list has the form
command1 && command2
command2 is executed if, and only if, command1 returns an exit status of zero.
An OR list has the form
command1 || command2
command2 is executed if and only if command1 returns a non-zero exit status. The return status of AND
and OR lists is the exit status of the last command executed in the list.