Thank you, bliako, for your suggestions. Unfortunately, strace is not available on my Mac. I wasn't able to coax any additional debug information. I also tried setting the $dl_debug flag.

I did modify the Rmath.pm file to use the DynaLoader module instead of XSLoader, sort of a reverse migration. The result was the same, even when pushing the exact .dylib folder path onto @DynaLoader::dl_library_path. When I add code to the .bs file, it is executed, so I used that to modify @DynaLoader::dl_library_path.

The default values for @DynaLoader::dl_library_path are '/usr/lib' and '/usr/local/lib'. The library loads correctly from either of those locations. I was able to load the library from other locations using the dl_load_file() function.

When I add code to the .bs file, it is executed, so I used that to modify @DynaLoader::dl_library_path.

What about adding that code in the actual .pm file you created (Rmath.pm?) like:

package Rmath;
...
our @ISA = qw( ... DynaLoader ... );

require DynaLoader;

push @DynaLoader::dl_library_path, 'my-nonstandard-lib-path';
print "XXX=$_\n" for @DynaLoader::dl_library_path;

bootstrap <Yourmodule> $VERSION;
[download]

$dl_debug : I meant doing export LD_DEBUG=all in your terminal/shell/prompt before testing your program (on that same terminal).

There are two very remote possibilities: 1) the dylib extension is not tried at all in enumerating possible library names (unlikely because it finds it in standard lib location), 2) the spaces in the library path (in OSX hmm that's not likely).

ps. the reason I suggested this reverse-migration is to investigate DynaLoader's behaviour without the front-man.

While trying your suggestion, I may have stumbled on the cause of my problem. I modified the .pm file as you suggested, and ran my test file. The library paths were printed as you'd expect, but the library still did not load. I wanted to be sure the library was actually where I specified, so I cd'd to that folder and did a directory listing. Then I ran the test file again, and the library loaded!!

WBBirkett-M:perl5 wbirkett$ cd ~/
WBBirkett-M:~ wbirkett$ perl -I/Users/wbirkett/Library/Application\ Su
+pport/TextMate/Pristine\ Copy/Bundles/PressCal.tmbundle/Support/lib/p
+erl5  /Users/wbirkett/Desktop/Rmath_test.pl
XXX=/usr/lib
XXX=/usr/local/lib
XXX=/Users/wbirkett/Library/Application Support/TextMate/Pristine Copy
+/Bundles/PressCal.tmbundle/Support/lib/perl5
Can't load '/Users/wbirkett/Library/Application Support/TextMate/Prist
+ine Copy/Bundles/PressCal.tmbundle/Support/lib/perl5/darwin-thread-mu
+lti-2level/auto/ICC/Support/Rmath/Rmath.bundle' for module ICC::Suppo
+rt::Rmath: dlopen(/Users/wbirkett/Library/Application Support/TextMat
+e/Pristine Copy/Bundles/PressCal.tmbundle/Support/lib/perl5/darwin-th
+read-multi-2level/auto/ICC/Support/Rmath/Rmath.bundle, 1): Library no
+t loaded: libRmath.dylib
  Referenced from: /Users/wbirkett/Library/Application Support/TextMat
+e/Pristine Copy/Bundles/PressCal.tmbundle/Support/lib/perl5/darwin-th
+read-multi-2level/auto/ICC/Support/Rmath/Rmath.bundle
  Reason: image not found at /System/Library/Perl/5.18/darwin-thread-m
+ulti-2level/DynaLoader.pm line 194.
 at /Users/wbirkett/Desktop/Rmath_test.pl line 1.
Compilation failed in require at /Users/wbirkett/Desktop/Rmath_test.pl
+ line 1.
BEGIN failed--compilation aborted at /Users/wbirkett/Desktop/Rmath_tes
+t.pl line 1.
WBBirkett-M:~ wbirkett$ cd /Users/wbirkett/Library/Application\ Suppor
+t/TextMate/Pristine\ Copy/Bundles/PressCal.tmbundle/Support/lib/perl5
WBBirkett-M:perl5 wbirkett$ perl -I/Users/wbirkett/Library/Application
+\ Support/TextMate/Pristine\ Copy/Bundles/PressCal.tmbundle/Support/l
+ib/perl5  /Users/wbirkett/Desktop/Rmath_test.pl
XXX=/usr/lib
XXX=/usr/local/lib
XXX=/Users/wbirkett/Library/Application Support/TextMate/Pristine Copy
+/Bundles/PressCal.tmbundle/Support/lib/perl5
OK
[download]

So, the failure to load the library is somehow connected to the current directory in the Terminal app. I don't know why that would matter, but it looks this is a macOS problem, not a Perl problem.

Thank you again for your help.

>strace is not available on my Mac

man dtruss

«...strace is not available on my Mac.»

dtruss?

«The Crux of the Biscuit is the Apostrophe»

perl -MCrypt::CBC -E 'say Crypt::CBC->new(-key=>'kgb',-cipher=>"Blowfish")->decrypt_hex($ENV{KARL});'Help