From @cpansprout

$ perl -le '$x = "6"; require $x'
Can't locate 6 in @​INC (@​INC contains​: /System/Library/Perl/5.10.1/darwin-thread-multi-2level /System/Library/Perl/5.10.1 /Library/Perl/5.10.1/darwin-thread-multi-2level /Library/Perl/5.10.1 /Library/Perl/5.10.0/darwin-thread-multi-2level /Library/Perl/5.10.0 /Library/Perl/5.8.9 /Library/Perl /Network/Library/Perl/5.10.1/darwin-thread-multi-2level /Network/Library/Perl/5.10.1 /Network/Library/Perl /System/Library/Perl/Extras/5.10.0/darwin-thread-multi-2level /System/Library/Perl/Extras/5.10.0 .) at -e line 1.

$ perl -le '$x = "6"; 0+$x; require $x'
Perl v6.0.0 required--this is only v5.10.1, stopped at -e line 1.

$ perl -le '$x = "34 cabbages"; 0+$x; require $x'
Perl v34.0.0 required--this is only v5.10.1, stopped at -e line 1.

$ perl5.12.4 -le '$x = "34 cabbages"; 0+$x; require $x'
Invalid version format (non-numeric data) at -e line 1.

In that last case it can’t decide whether to use the numeric or string representation.

I was actually surprised to find that require ${\6} works the way it does. I thought that require NUMBER was a syntactic special case like require BEARWORD.

Would it break anything to make it such a special case?

Flags​:
  category=core
  severity=low

Site configuration information for perl 5.15.5​:

Configured by sprout at Sat Nov 26 11​:40​:22 PST 2011.

Summary of my perl5 (revision 5 version 15 subversion 5) configuration​:
  Snapshot of​: c071f8d
  Platform​:
  osname=darwin, osvers=10.5.0, archname=darwin-thread-multi-2level
  uname='darwin pint.local 10.5.0 darwin kernel version 10.5.0​: fri nov 5 23​:20​:39 pdt 2010; root​:xnu-1504.9.17~1release_i386 i386 '
  config_args='-de -Dusedevel -Duseithreads -Dmad'
  hint=recommended, useposix=true, d_sigaction=define
  useithreads=define, usemultiplicity=define
  useperlio=define, d_sfio=undef, uselargefiles=define, usesocks=undef
  use64bitint=undef, use64bitall=undef, uselongdouble=undef
  usemymalloc=n, bincompat5005=undef
  Compiler​:
  cc='cc', ccflags ='-fno-common -DPERL_DARWIN -fno-strict-aliasing -pipe -fstack-protector -I/usr/local/include',
  optimize='-O3',
  cppflags='-fno-common -DPERL_DARWIN -fno-strict-aliasing -pipe -fstack-protector -I/usr/local/include'
  ccversion='', gccversion='4.2.1 (Apple Inc. build 5664)', gccosandvers=''
  intsize=4, longsize=4, ptrsize=4, doublesize=8, byteorder=1234
  d_longlong=define, longlongsize=8, d_longdbl=define, longdblsize=16
  ivtype='long', ivsize=4, nvtype='double', nvsize=8, Off_t='off_t', lseeksize=8
  alignbytes=8, prototype=define
  Linker and Libraries​:
  ld='env MACOSX_DEPLOYMENT_TARGET=10.3 cc', ldflags =' -fstack-protector -L/usr/local/lib'
  libpth=/usr/local/lib /usr/lib
  libs=-ldbm -ldl -lm -lutil -lc
  perllibs=-ldl -lm -lutil -lc
  libc=, so=dylib, useshrplib=false, libperl=libperl.a
  gnulibc_version=''
  Dynamic Linking​:
  dlsrc=dl_dlopen.xs, dlext=bundle, d_dlsymun=undef, ccdlflags=' '
  cccdlflags=' ', lddlflags=' -bundle -undefined dynamic_lookup -L/usr/local/lib -fstack-protector'

Locally applied patches​:
 

@​INC for perl 5.15.5​:
  /usr/local/lib/perl5/site_perl/5.15.5/darwin-thread-multi-2level
  /usr/local/lib/perl5/site_perl/5.15.5
  /usr/local/lib/perl5/5.15.5/darwin-thread-multi-2level
  /usr/local/lib/perl5/5.15.5
  /usr/local/lib/perl5/site_perl
  .

Environment for perl 5.15.5​:
  DYLD_LIBRARY_PATH (unset)
  HOME=/Users/sprout
  LANG=en_US.UTF-8
  LANGUAGE (unset)
  LD_LIBRARY_PATH (unset)
  LOGDIR (unset)
  PATH=/usr/bin​:/bin​:/usr/sbin​:/sbin​:/usr/local/bin​:/usr/X11/bin​:/usr/local/bin
  PERL_BADLANG (unset)
  SHELL=/bin/bash