Книга: Linux Network Administrator Guide, Second Edition
Comments
Comments
Lines in the sendmail.mc file that begin with the # character are not parsed by m4, and will by default be output directly into the sendmail.cf file. This is useful if you want to comment on what your configuration is doing in both the input and output files.
To allow comments in your sendmail.mc that are not placed into the sendmail.cf, you can use the m4 divert and dnl tokens. divert(-1) will cause all output to cease. divert(0) will cause output to be restored to the default. Any output generated by lines between these will be discarded. In our example, we've used this mechanism to provide a comment that appears only in the sendmail.mc file. To achieve the same result for a single line, you can use the dnl token that means, literally, "starting at the beginning of the next line, delete all characters up to and including the next newline." We've used this in our example, too.
These are standard m4 features, and you can obtain more information on them from its manual page.
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