5.005_57: Regex behaves incorrectly

[p5pRT]

Migrated from rt.perl.org#844 (status was 'resolved')

Searchable as RT844$

[p5pRT]

From @mjdominus

This should print `!!!' before it does anything else, and in this case
the regex should match. (It's a slightly modified version of the
regex from page 200 of _Perl Cookbook_; it should match any string
that does not end in `foo'.

However, it doesn't match, and it doesn't print `!!!' either.

If I remove the $ from the end of the regex, it prints `!!!'.
If I remove (?{print "$2 "}) from the middle, it prints `!!!'.
If I change the target string from `xf' to `x', it prints `!!!'.

Summary of my perl5 (revision 5.0 version 5 subversion 57) configuration​:
  Platform​:
  osname=linux, osvers=2.0.35, archname=i586-linux
  uname='linux plover 2.0.35 #2 mon oct 26 21​:26​:00 cst 1998 i586 unknown '
  config_args='-Doptimize=-g -des'
  hint=recommended, useposix=true, d_sigaction=define
  usethreads=undef useperlio=undef d_sfio=undef
  use64bits=undef usemultiplicity=undef
  Compiler​:
  cc='cc', optimize='-g', gccversion=egcs-2.90.29 980515 (egcs-1.0.3 release)
  cppflags='-Dbool=char -DHAS_BOOL -DDEBUGGING -I/usr/local/include'
  ccflags ='-Dbool=char -DHAS_BOOL -DDEBUGGING -I/usr/local/include'
  stdchar='char', d_stdstdio=define, usevfork=false
  intsize=4, longsize=4, ptrsize=4, doublesize=8
  d_longlong=define, longlongsize=8, d_longdbl=define, longdblsize=12
  alignbytes=4, usemymalloc=n, prototype=define
  Linker and Libraries​:
  ld='cc', ldflags =' -L/usr/local/lib'
  libpth=/usr/local/lib /shlib /lib /usr/lib
  libs=-lndbm -lgdbm -ldbm -ldb -ldl -lm -lc
  libc=/lib/libc-2.0.7.so, so=so, useshrplib=false, libperl=libperl.a
  Dynamic Linking​:
  dlsrc=dl_dlopen.xs, dlext=so, d_dlsymun=undef, ccdlflags='-rdynamic'
  cccdlflags='-fpic', lddlflags='-shared -L/usr/local/lib'

Characteristics of this binary (from libperl)​:
  Compile-time options​: DEBUGGING
  Built under linux
  Compiled at May 25 1999 16​:00​:13
  @​INC​:
  /usr/local/lib/perl5/5.00557/i586-linux
  /usr/local/lib/perl5/5.00557
  /usr/local/lib/perl5/site_perl/5.00557/i586-linux
  /usr/local/lib/perl5/site_perl/5.00557
  .

Mark-Jason Dominus mjd@​plover.com

[p5pRT]

From [Unknown Contact. See original ticket]

Mark,

The code you gave​:

  #!/usr/bin/perl -w

  $z = ("xf" =~ m{^
  (?{print "!!!\n"})
  (
  (
  (?!foo$ )
  .
  ) (?{print "$2 "})
  *
  )
  $
  }x);

  print "$z\n";

now emits a warning (in 5.6-RC2)​:

(?{print "$2 "})
*
matches null string many times at /tmp/asdf line 13.

I don't know whether this helps your code or reflects a different
bug :-)

Nat

[p5pRT]

From @mjdominus

Mark,

The code you gave​:

The warning makes sense, and I can't imagine what possessed me to put a
* there. Can you send me some private email to remind me of the
context?