/usr/bin/perl -w /tmp/plre2el.pl 
Perlcode: "(.*?)"
Elispcode: \"\\(.*?\\)\"
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use strict;
use warnings;
 
 # version 0.2
 
 $\="\n";
 
 #--- flags  
 my $flag_interactive; # true => no extra escaping of backslashes
 
 
 my $RE='\w*(a|b|c)\d\(';
 $RE='\d{2,3}';
 $RE='"(.*?)"';
 
 print "Perlcode: $RE";
 
 #--- hide pairs of backslashes
 $RE=~s#\\\\#\0#g;
 
 # TODO check for suitable long "hidesequence" instead of a simple \0
 
 #--- TODO normalisation of needless escaping
 # e.g.  from /\"/ to /"/, since it's no difference in perl but might 
+confuse elisp
 
  
 #--- toggle escaping of 'backslash constructs'
 my $bsc='(){}|';
 $RE=~s#[$bsc]#\\$&#g;  # escape them once
 $RE=~s#\\\\##g;        # and erase double-escaping
 
 
 
 #--- replace character classes
 my %charclass=(
         w => 'word' ,   # TODO: emacs22 already knows \w ???
         d => 'digit',
         s => 'space'
        );
 
 my $kc=join "|",keys %charclass;
 $RE=~s#\\($kc)#[[:$charclass{$1}:]]#g; 
 
 
 
 #--- unhide pairs of backslashes
 $RE=~s#\0#\\\\#g;
 
 #--- escaping for elisp string
 unless ($flag_interactive){
   $RE=~s#\\#\\\\#g; # ... backslashes
   $RE=~s#"#\\"#g;   # ... quotes
 }
 
 
 print "Elispcode: $RE";
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Please note: xemacs knows "Raw Strings" where escaping is not neccessary, but I doubt that normal Perl RE syntax can be used from within Gnu Emacs Lisp because of the quoting problem, so the conversion can in general only be done with perl!

UPDATE:

-TODO: Just noticed that i still need a special treatment for escape sequences like \t and \n. I'll add this tomorrow.

last version re_pl2el.pl

use strict;
use warnings;
 
# version 0.3
 
$\="\n";
 
 
# TODO
# * wrap converter to function
# * testsuite
 
#--- flags  
my $flag_interactive; # true => no extra escaping of backslashes
 
 
my $RE='\w*(a|b|c)\d\(';
$RE='\d{2,3}';
$RE='"(.*?)"';
$RE="\0".'\"\t(.*?)"';
 
print "Perlcode:\t $RE";
 
#--- encode all \0 chars as escape sequence
$RE=~s#\0#\\0#g;
 
#--- substitute pairs of backslashes with \0
$RE=~s#\\\\#\0#g;
 
#--- hide escape sequences of \t,\n,... with 
#    corresponding ascii code
my %ascii=(
       t =>"\t",
       n=> "\n"
      );
my $kascii=join "|",keys %ascii;
 
$RE=~s#\\($kascii)#$ascii{$1}#g;
 
 
#---  normalize needless escaping
# e.g.  from /\"/ to /"/, since it's no difference in perl 
# but might confuse elisp
 
$RE=~s#\\"#"#g;
 
#--- toggle escaping of 'backslash constructs'
my $bsc='(){}|';
$RE=~s#[$bsc]#\\$&#g;  # escape them once
$RE=~s#\\\\##g;        # and erase double-escaping
 
 
 
#--- replace character classes
my %charclass=(
        w => 'word' ,   # TODO: emacs22 already knows \w ???
        d => 'digit',
        s => 'space'
       );
 
my $kc=join "|",keys %charclass;
$RE=~s#\\($kc)#[[:$charclass{$1}:]]#g; 
 
 
 
#--- unhide pairs of backslashes
$RE=~s#\0#\\\\#g;
 
#--- escaping for elisp string
unless ($flag_interactive){
  $RE=~s#\\#\\\\#g; # ... backslashes
  $RE=~s#"#\\"#g;   # ... quotes
}
 
#--- unhide escape sequences of \t,\n,...
my %rascii= reverse %ascii;
my $vascii=join "|",keys %rascii;
$RE=~s#($vascii)#\\$rascii{$1}#g;
 
print "Elispcode:\t $RE";
 
#TODO whats the elisp syntax for \0 ???
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