strict and warnings would have given you a clue:

print (...) interpreted as function at C:\test.pl line 11.
syntax error at C:\test.pl line 11, near ")["
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From perldiag:

%s (...) interpreted as function
(W syntax) You've run afoul of the rule that says that any list operator followed by parentheses turns into a function, with all the list operators arguments found inside the parentheses. See Terms and List Operators (Leftward) in the perlop manpage.

I'm not a guru on these things, but I think the parens you used to place the regex in list context (and take the slice) are interpreted by perl to be the optional parens around the arguments to the print function. You need an extra set to make everything happy:

print( ('abcd' =~ /(\w)\w(\w)/ )[0] ); # prints 'a'
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Update: Yup, that was it. Added diagnostic message from perldiag.

I think you wanted:

print +('abcd' =~ /(\w)\w(\w)/ )[0];
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/J\

You could also use printf, which expects its first argument to be a format string, like so:

printf "%s", ('abcd' =~ /(\w)\w(\w)/ )[0];
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Always add use strict; use warnings; at the start of your script. If you had done so you would have received the error:

print (...) interpreted as function at ...
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and saved everyone some time. :)

I had yet to run it in context, where I DO have warnings and strict on. I encountered the error while running perl -c on a mason component I wrote.

my $id = $ARGS{to} || ( $m->dhandler_arg =~ /^(\w+)\/pledge/ )[0]; is the offending line. ( $m->dhandler_arg =~ /^(\w+)\/pledge/ )[0] seemed to be the offending part, so I pulled it out for examination.

I used a print statement for testing. I should have run perl -We instead of -e on my test case. Also, I should have used a more accurate test case, as I seem to have gone hunting for the a problem I didn't originally have (and found it!)

"One is enough. If you are acquainted with the principle, what do you care for the myriad instances and applications?"
- Henry David Thoreau, Walden