Comment (by Roland Haas):

Cactus' build system uses the make (and thus shell) variable $PERL for the location of the configured Perl interpreter. This cannot quite be used in the #! line since that line does not do variable expansion.

We also cannot use any options of env other than the ones in POSIX: https://pubs.opengroup.org/onlinepubs/9699919799/utilities/env.html so -S is not possible (though it does seems to be supported on Linux and macOS). Otherwise using something like env -S ${PERL} -w would be great.

Instead the Cactus make files run perl scripts as $PERL foo.pl and the scripts should use use warnings; instead of the -w switch.

Is that something that you could give a try? I am not sure what other scripts in Formaline exist that are directly called and not already via $PERL.

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Ticket URL: https://bitbucket.org/einsteintoolkit/tickets/issues/2811/formaline-optionally-use-non-system-perl