The extra trailing space is explainable to the weird use the OP is making of pack: 

#!/usr/bin/perl -w
use strict;
use Win32::API;
Win32::API->Import("kernel32", "LPTSTR GetCommandLine()");

my $cl = GetCommandLine();
printf "%d : '%s'\n", length( $cl ), $cl;

my $cl2 = pack 'Z*', GetCommandLine();
printf "%d : '%s'\n", length( $cl2 ), $cl2;

__END__
C:\test>junk3
46 : '"c:\perl\bin\perl.exe" -sw "C:\test\junk3.pl" '
47 : '"c:\perl\bin\perl.exe" -sw "C:\test\junk3.pl"  '

[download]

I'm lost as to why the combination of pack, mingw built perl and a batch file would cause a segfault?

Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
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In the absence of evidence, opinion is indistinguishable from prejudice.
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In reply to Re^6: Win32::API Memory Exception with GetCommandLine() (which returns a static string) by BrowserUk
in thread Win32::API Memory Exception with GetCommandLine() (which returns a static string) by Wyrdweaver

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