(bashref.info)Shell Syntax

   When the shell reads input, it proceeds through a sequence of
operations.  If the input indicates the beginning of a comment, the
shell ignores the comment symbol (`#'), and the rest of that line.

   Otherwise, roughly speaking,  the shell reads its input and divides
the input into words and operators, employing the quoting rules to
select which meanings to assign various words and characters.

   The shell then parses these tokens into commands and other
constructs, removes the special meaning of certain words or characters,
expands others, redirects input and output as needed, executes the
specified command, waits for the command's exit status, and makes that
exit status available for further inspection or processing.