Re: commenting a *make* directive that is a *shell* command

[Greg Chicares]

On 2006-2-13 13:50 UTC, Robert P. J. Day wrote:
> 
> all:
>       # $(warning whatever)
> 
>   that command above has a leading tab so, according to the docs, it
> should be treated as a shell command.  but it's clearly the make
> warning built-in and, even with that "#", it's processed by make as a
> warning.  why?

The manual says this of $(error):
| Note that the error is generated whenever this function is evaluated.
| So, if you put it inside a command script or on the right side of a
| recursive variable assignment, it won't be evaluated until later.
| The text will be expanded before the error is generated.
and $(warning) works the same way.

Make needs to pass the command
  # $(warning whatever)
to the shell; when it does so, it evaluates '$(warning whatever)'.

Make doesn't require that the shell interpret a command beginning
with '#' as a comment. The manual says:
| `#' in a line of a makefile starts a comment. [...but...]
| Within a command script (if the line begins with a TAB character)
| the entire line is passed to the shell, just as with any other line
| that begins with a TAB. The shell decides how to interpret the text:
| whether or not this is a comment is up to the shell.

>   if i remove that leading tab, then, of course, it's commented out
> and does what i would have expected.  so what's happening above?

In that case, it's not a shell command that happens to begin with '#';
it's a make comment.