/usr/bin/perl -w /tmp/plre2el.pl 
Perlcode: "(.*?)"
Elispcode: \"\\(.*?\\)\"

##</code><code>##

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";
 
##</code><code>##

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 ???