(autoconf.info)Special Chars in Variables

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7.3 Special Characters in Output Variables

Many output variables are intended to be evaluated both by `make' and
by the shell.  Some characters are expanded differently in these two
contexts, so to avoid confusion these variables' values should not
contain any of the following characters:

     " # $ & ' ( ) * ; < > ? [ \ ^ ` |

   Also, these variables' values should neither contain newlines, nor
start with `~', nor contain white space or `:' immediately followed by
`~'.  The values can contain nonempty sequences of white space
characters like tabs and spaces, but each such sequence might
arbitrarily be replaced by a single space during substitution.

   These restrictions apply both to the values that `configure'
computes, and to the values set directly by the user.  For example, the
following invocations of `configure' are problematic, since they
attempt to use special characters within `CPPFLAGS' and white space
within `$(srcdir)':

     CPPFLAGS='-DOUCH="&\"#$*?"' '../My Source/ouch-1.0/configure'

     '../My Source/ouch-1.0/configure' CPPFLAGS='-DOUCH="&\"#$*?"'

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