Comments (Bash Reference Manual)
In a non-interactive shell, or an interactive shell in which the
interactive_comments option to the
shopt builtin is enabled (see The Shopt Builtin), a word beginning with ‘
#’ causes that word and all remaining characters on that line to be ignored. An interactive shell without the
interactive_comments option enabled does not allow comments. The
interactive_comments option is on by default in interactive shells. See Interactive Shells, for a description of what makes a shell interactive.