21.5.1 Syntactic conventions
Some conventions have grown over the life of the GNU Autotools, mostly as a
disciplined way of avoiding M4 pitfalls. These conventions
are designed to make your macros more robust, your code easier to read
and, most importantly, improve your chances for getting things to work
the first time! A brief list of recommended conventions appears below:
Do not use the M4 built-in
changequote. Any good macro
will already perform sufficient quoting.
Never use the argument macros (e.g. `$1') within shell comments and
dnl remarks. If such a comment were to be placed within a macro
definition, M4 will expand the argument macros leading to strange
results. Instead, quote the argument number to prevent unwanted
expansion. For instance, you would use `$' in the comment.
Quote the M4 comment character, `#'. This can appear often in
shell code fragments and can have undesirable effects if M4 ignores any
expansions in the text between the `#' and the next newline.
In general, macros invoked from `configure.in' should be placed one
per line. Many of the GNU Autotools macros conclude their definitions with
dnl to prevent unwanted whitespace from accumulating in
Many of the
AC_ macros, and others which emulate their good
behavior, permit default values for unspecified arguments. It is
considered good style to explicitly show your intention to use an empty
argument by using a pair of quotes, such as
- Always quote the names of macros used within the definitions of
- When writing new macros, generate a small `configure.in' that
uses (and abuses!) the macro--particularly with respect to quoting.
Generate a `configure' script with
autoconf and inspect