In a makefile, a hash mark (#) anywhere in a line begins a comment, unless the line is a command. make ignores comments, as if the text from the hash mark to the end of its line did not exist. Comments (like blank lines) between the lines of a rule do not interrupt its continuity. Leading whitespace before a hash mark is ignored.
If a line containing a hash mark is a commandthat is, if it begins with a tab characterthen it cannot contain a make comment. If the corresponding target needs to be built, make passes the entire command line, minus the leading tab character, to the shell for execution. (Some shells, such as the Bourne shell, also interpret the hash mark as introducing a comment, but that is beyond make's control.)