SPUG: Strange regex problem

[Matt Tucker]

-- Trevor Leffler <tleffler at u.washington.edu> spake thusly:

>   I'm working with a substitution regex that correctly does a
> substitution, but the $1, $2, etc. that I expect are empty when I use
> the //i and //g modifiers together.  I am hoping that one of you may
> have seen this before and have a good explanation; why would they
> react to one another?  Please ignore that the //i and //g are
> pointless in my example, except for demonstrating this problem.  Here
> is an example of what I'm talking about (using the ever-so-cute abc
> regex):
>
> # Just using //i here
> bash$ perl -e '$foo = "abcdefghijklmnopqrstuvwxyz"; $foo =~
> s/(hi)(.*)(stu)/$3$2$1/i; print "$1, $3!\n$foo\n"'
> hi, stu!
> abcdefgstujklmnopqrhivwxyz
>
> # //g here, and still no problems with $1, $2, and $3
> bash$ perl -e '$foo = "abcdefghijklmnopqrstuvwxyz"; $foo =~
> s/(hi)(.*)(stu)/$3$2$1/g; print "$1, $3!\n$foo\n"'
> hi, stu!
> abcdefgstujklmnopqrhivwxyz
>
> #  Whoops!  //gi is acting fishy...
> bash$ perl -e '$foo = "abcdefghijklmnopqrstuvwxyz"; $foo =~
> s/(hi)(.*)(stu)/$3$2$1/gi; print "$1, $3!\n$foo\n"'
> , !
> abcdefgstujklmnopqrhivwxyz

This seems to be fixed in 5.6:

[2] mtucker at benzene$ perl -e '$foo = "abcdefghijklmnopqrstuvwxyz"; $foo 
=~ s/(hi)(.*)(stu)/$3$2$1/gi; print "$1, $3!\n$foo\n"'
hi, stu!
abcdefgstujklmnopqrhivwxyz





[3] mtucker at benzene$ perl -V
Summary of my perl5 (revision 5.0 version 6 subversion 0) configuration:
  Platform:
    osname=linux, osvers=2.2.15-0.16mdksmp, archname=i386-linux
    uname='linux kenobi.mandrakesoft.com 2.2.15-0.16mdksmp #1 smp mon 
mar 13 16:40:10 cet 2000 i686 unknown '
    config_args='-des -Dprefix=/usr -Darchname=i386-linux -Dd_dosuid 
-Dd_semctl_semun -Di_db -Di_ndbm -Di_gdbm -Ud_csh 
-Dman3dir=/usr/lib/perl5/man/man3 -Doptimize=-O3 -fomit-frame-pointer 
-fno-exceptions -fno-rtti -pipe -s -mpentium -mcpu=pentium 
-march=pentium -ffast-math -fexpensive-optimizations'
    hint=recommended, useposix=true, d_sigaction=define
    usethreads=undef use5005threads=undef useithreads=undef 
usemultiplicity=undef
    useperlio=undef d_sfio=undef uselargefiles=define
    use64bitint=undef use64bitall=undef uselongdouble=undef 
usesocks=undef
  Compiler:
    cc='cc', optimize='-O3 -fomit-frame-pointer -fno-exceptions 
-fno-rtti -pipe -s -mpentium -mcpu=pentium -march=pentium -ffast-math 
-fexpensive-optimizations', gccversion=2.95.3 19991030 (prerelease)
    cppflags='-fno-strict-aliasing'
    ccflags ='-fno-strict-aliasing -D_LARGEFILE_SOURCE 
-D_FILE_OFFSET_BITS=64'
    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
    ivtype='long', ivsize=4, nvtype='double', nvsize=8, Off_t='off_t', 
lseeksize=8
    alignbytes=4, usemymalloc=n, prototype=define
  Linker and Libraries:
    ld='cc', ldflags =' -L/usr/local/lib'
    libpth=/usr/local/lib /lib /usr/lib
    libs=-lnsl -ldl -lm -lc -lposix -lcrypt
    libc=/lib/libc-2.1.3.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: USE_LARGE_FILES
  Built under linux
  Compiled at Mar 28 2000 16:22:07
  %ENV:
    PERL5LIB="/home/mtucker/lib"
  @INC:
    /home/mtucker/lib
    /usr/lib/perl5/5.6.0/i386-linux
    /usr/lib/perl5/5.6.0
    /usr/lib/perl5/site_perl/5.6.0/i386-linux
    /usr/lib/perl5/site_perl/5.6.0
    /usr/lib/perl5/site_perl/5.005/i386-linux
    /usr/lib/perl5/site_perl/5.005
    /usr/lib/perl5/site_perl


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