C:\_32\pscrpt>perl try.pl
Use of uninitialized value in undef operator at try.pl line 4.
Successful command returning 1
![] ?[256 : 1] E[The specified image file did not contain a resource s
+ection]
Use of uninitialized value in undef operator at try.pl line 10.

Nonexistent command, attempted direct but fallback to via cmd
'c:/doesNotExists.exe' is not recognized as an internal or external co
+mmand,
operable program or batch file.
![No such file or directory] ?[256 : 1] E[There are no more files]
Use of uninitialized value in undef operator at try.pl line 16.

Nonexistent via cmd because 'shell chars'; sending stderr >null
![] ?[256 : 1] E[There are no more files]
[download]

BrowserUk/Rob, your responses are gold. Your answers are exactly the sort of information I was after.

However it appears that $^E isn't yet my saviour. Under my Windows XP system I get the following results (uninitalized warnings trimmed):

#! perl -slw
use strict;

undef $^E;
undef $!;
print 'Successful command returning 1';
system 'c:/perl/bin/perl.exe -e"sleep 5; exit 1"';
print "![$!] ?[@{[$?, ':', $?>>8]}] E[$^E]";

undef $^E;
undef $!;
print "\nNonexistent command, attempted direct but fallback to via cmd
+";
system 'c:/doesNotExists.exe';
print "![$!] ?[@{[$?, ':', $?>>8]}] E[$^E]";

undef $^E;
undef $!;
print "\nNonexistent via cmd because 'shell chars'; sending stderr >nu
+ll";
system 'c:/doesNotExists.exe 2>null';
print "![$!] ?[@{[$?, ':', $?>>8]}] E[$^E]";
__END__
Successful command returning 1
![] ?[256 : 1] E[]

Nonexistent command, attempted direct but fallback to via cmd
'c:/doesNotExists.exe' is not recognized as an internal or external co
+mmand, operable program or batch file.
![No such file or directory] ?[256 : 1] E[]

Nonexistent via cmd because 'shell chars'; sending stderr >null
![] ?[256 : 1] E[]
[download]

It appears that redirecting stderr makes an unsuccessful command appear to be a successful command. When an error does occur, it's found inside $! and not $^E, which seems to never be set. Oh my!

Unfortunately this leaves me with the same tangle as Perl itself has in emulating system() under Windows. Ideally I want to preserve the following behaviours:

1. Single argument call always goes via the shell
2. Multi argument call never goes via the shell
3. It's possible to tell when a command didn't start (ostensibly via $? being set to -1)

Using the shell means I don't have a reliable way of determining failure to start a command. Not using the shell means I may have to potentially go searching through $ENV{PATH} by hand.

I guess this is an excellent opportunity for me to go searching for that discussion by tye, and potentially go looking through Perl's source for system() under Windows. I suspect my final result will make heavy use of Win32:: modules to provide the required behaviour.

Many thanks again!

Update: Working with Win32::Process is showing great promise.

Paul Fenwick
Perl Training Australia

When an error does occur, it's found inside $! and not $^E

Could $! then be used (instead of $^E) to determine the info you need ? Looking at what you, BrowserUk, and I have posted, it seems that $! might be all you need to consider (so long as it's undeffed before the system call). Or am I missing something ?

Cheers,
Rob
Update: I have no problem with Paul's preference for Win32::Process. The variablility in $^E and $!, wrt to system(), doesn't inspire a lot of confidence.