$ perl -d:Foo -e1
Can't locate Devel/Foo.pm in @INC (...)

$ perl -d:Foo=opt -e1
Can't find string terminator ";" anywhere before EOF.

##</code><code>##


$ echo 1 | perl -d:Foo=v
Can't find string terminator ";" anywhere before EOF.

$ echo 1 > a; perl -d:Foo=v a
Can't find string terminator ";" anywhere before EOF.

$ perl -d:Foo=v -e';1'
Number found where operator expected at -e line 1, near ";1"
  (Might be a runaway multi-line ;; string starting on line 0)
        (Missing operator before 1?)
syntax error at -e line 1, near ";1"
Execution of -e aborted due to compilation errors.

$ debugperl -DT -d:Foo=opt -e1
### 0:LEX_NORMAL/XSTATE "\n;"
### <== USE(ival=1)

### 0:LEX_KNOWNEXT/XTERM "split(/,/,q;\n"
### <== WORD(opval=null)

### 0:LEX_KNOWNEXT/XTERM "split(/,/,q;\n"
### <== WORD(opval=op_const) PV("Devel::Foo"\0)

### 0:LEX_NORMAL/XSTATE "split(/,/,q;\n"
### <== FUNC(ival=op_split)

### 0:LEX_NORMAL/XTERM "(/,/,q;\n"
### <== '('

### 0:LEX_NORMAL/XTERM "/,/,q;\n"
### <== PMFUNC(opval=op_match)

### 0:LEX_INTERPPUSH/XTERM ",q;\n"
### <== '('

### 0:LEX_INTERPCONCAT/XTERM ","
### 0:LEX_KNOWNEXT/XTERM ""
### <== THING(opval=op_const) PV(","\0)

### 0:LEX_INTERPSTART/XTERM ""
### <== ')'

### 0:LEX_NORMAL/XOPERATOR ",q;\n"
### <== ','

### 0:LEX_NORMAL/XTERM "q;\n"
Can't find string terminator ";" anywhere before EOF.



$ perl -d:Foo=v -e';);die 123;'
Can't locate Devel/Foo.pm in @INC (...)

$ echo 'sub DB::DB { }; 1' > lib/Devel/Foo.pm
$ perl -d:Foo=v -e';);die 123;'
123 at -e line 1.

$ cat lib/Devel/Foo.pm 
package Devel::Foo;

sub DB::DB { }
sub import {
    warn @{'::_<-e'};
}
1;
__DATA__

$ perl -d:Foo=v -e';);die 123;'
use Devel::Foo split(/,/,q;
;);die 123;
123 at -e line 1.


$ vi perl-5.8.8/perl.c +3089
    case 'd':
        forbid_setid("-d");
        s++;
        
        /* -dt indicates to the debugger that threads will be used */
        if (*s == 't' && !isALNUM(s[1])) {
            ++s;
            my_setenv("PERL5DB_THREADED", "1");
        }
        
        /* The following permits -d:Mod to accepts arguments following an =
           in the fashion that -MSome::Mod does. */
        if (*s == ':' || *s == '=') {
            const char *start;
            SV *sv;
            sv = newSVpv("use Devel::", 0);
            start = ++s;
            /* We now allow -d:Module=Foo,Bar */
            while(isALNUM(*s) || *s==':') ++s;
            if (*s != '=')
                sv_catpv(sv, start);
            else {
                sv_catpvn(sv, start, s-start);
                Perl_sv_catpvf(aTHX_ sv, " split(/,/,q%c%s%c)", 0, ++s, 0);
            }  
            s += strlen(s);
            my_setenv("PERL5DB", (char *)SvPV_nolen_const(sv));
        }
        if (!PL_perldb) {
            PL_perldb = PERLDB_ALL;
            init_debugger();
        }
        return s;

The equivalent bit for -M and -m processing (perl.c line 3232):

                sv_catpvn(sv, start, s-start);
                sv_catpv(sv, " split(/,/,q");
                sv_catpvn(sv, "\0)", 1);        /* Use NUL as q//-delimiter. */
                sv_catpv(sv, ++s);
                sv_catpvn(sv,  "\0)", 2);

$ perl -d:Foo -MDevel::Foo=1 -e'die 123;'
use Devel::Foo;use Devel::Foo split(/,/,q1);
use Devel::Foo;use Devel::Foo split(/,/,q1);
123 at -e line 1.

Hmm, maybe this is related to sprintf and "\0" via Perl_sv_catpvf above

$ perl -d:Foo -MDevel::Foo=1 -e'die 123;' 2>&1 | od -c
0000000   u   s   e       D   e   v   e   l   :   :   F   o   o   ;   u
0000020   s   e       D   e   v   e   l   :   :   F   o   o       s   p
0000040   l   i   t   (   /   ,   /   ,   q  \0   1  \0   )   ;  \n   u
0000060   s   e       D   e   v   e   l   :   :   F   o   o   ;   u   s
0000100   e       D   e   v   e   l   :   :   F   o   o       s   p   l
0000120   i   t   (   /   ,   /   ,   q  \0   1  \0   )   ;  \n   1   2
0000140   3       a   t       -   e       l   i   n   e       1   .  \n
0000160

$ perl -d:Foo=v -e';);die 123;' 2>&1 | od -c
0000000   u   s   e       D   e   v   e   l   :   :   F   o   o       s
0000020   p   l   i   t   (   /   ,   /   ,   q   ;  \n   ;   )   ;   d
0000040   i   e       1   2   3   ;  \n   1   2   3       a   t       -
0000060   e       l   i   n   e       1   .  \n
0000072

$ grep -r -- -d: perl-5.8.8/t
perl-5.8.8/t/run/switchd.t:              switches => [ '-Ilib', '-d:switchd' ],

I don't think this is currently tested

perl-5.8.8]$ diff -u ./t/run/switchd.t ./t/run/new_switchd.t 
--- ./t/run/switchd.t   2003-05-24 17:49:13.000000000 +1000
+++ ./t/run/new_switchd.t       2007-10-07 15:49:52.000000000 +1000
@@ -7,7 +7,7 @@
 
 require "./test.pl";
 
-plan(tests => 1);
+plan(tests => 2);
 
 my $r;
 my @tmpfiles = ();
@@ -36,5 +36,11 @@
                 progfile => $filename,
                );
     like($r, qr/^main,swdtest.tmp,9;Foo,swdtest.tmp,5;Foo,swdtest.tmp...
+
+    $r = runperl(
+                switches => [ '-Ilib', '-d:switchd=1,2' ],
+                progfile => $filename,
+               );
+    like($r, qr/^main,swdtest.tmp,9;Foo,swdtest.tmp,5;Foo,swdtest.t...


perl-5.8.8]$ perl ./t/run/new_switchd.t 
1..2
ok 1
syntax error at swdtest.tmp line 2, near "sub bar "
  (Might be a runaway multi-line ;; string starting on line 0)
Execution of swdtest.tmp aborted due to compilation errors.
not ok 2
# Failed at ./t/run/new_switchd.t line 44
#      got ''
# expected /(?i-xsm:^main,swdtest.tmp,9;Foo,swdtest...