texinfo: Testing for Texinfo Commands

Conditionals

Conditional Nesting

@set @clear @value

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18.6 Testing for Texinfo Commands: '@ifcommanddefined', '@ifcommandnotdefined'
==============================================================================

Occasionally, you may want to arrange for your manual to test if a given
Texinfo command is available and (presumably) do some sort of fallback
formatting if not.  There are conditionals '@ifcommanddefined' and
'@ifcommandnotdefined' to do this.  For example:

     @ifcommanddefined node
     Good, @samp{@@node} is defined.
     @end ifcommanddefined

will output the expected 'Good, '@node' is defined.'.

  This conditional will also consider true any new commands defined by
the document via '@macro', '@alias', '@definfoenclose', and
'@def(code)index' (Note: Defining New Texinfo Commands).  Caveat: the
TeX implementation reports internal TeX commands, in addition to all the
Texinfo commands, as being "defined"; the 'makeinfo' implementation is
reliable in this regard, however.

  You can check the 'NEWS' file in the Texinfo source distribution and
linked from the Texinfo home page
(<http://www.gnu.org/software/texinfo>) to see when a particular command
was added.

  These command-checking conditionals themselves were added in
Texinfo 5.0, released in 2013--decades after Texinfo's inception.  In
order to test if they themselves are available, the predefined flag
'txicommandconditionals' can be tested, like this:

     @ifset txicommandconditionals
     @ifcommandnotdefined foobarnode
     (Good, @foobarnode is not defined.)
     @end ifcommandnotdefined
     @end ifset

  Since flags (see the previous section) were added early in the
existence of Texinfo, there is no problem with assuming they are
available.

  We recommend avoiding these tests whenever possible--which is usually
the case.  For many software packages, it is reasonable for all
developers to have a given version of Texinfo (or newer) installed, and
thus no reason to worry about older versions.  (It is simple to download
and install the Texinfo source; it does not have any problematic
dependencies.)

  The issue of Texinfo versions does not generally arise for end-users.
With properly distributed packages, users need not process the Texinfo
manual simply to build and install the package; they can use
preformatted Info (or other) output files.  This is desirable in
general, to avoid unnecessary dependencies between packages (Note:
(standard)Releases).