Backslashes in double quotes behave differently from backslashes in single quotes. Your \t in c:\temp gets interpreted as tab character in double quoted strings. See perlop.

The solution is to check the command you're about to execute:

my $cmd = "ping $_ >c:\temp\log.txt";
print "About to run [$cmd]\n";
system($cmd) == 0
    or die "Couldn't run [$cmd]: $!/$?/$^E";
[download]

In the short run, doubling all backslashes will do what you want:

my $cmd = "ping $_ >c:\\temp\\log.txt";
print "About to run [$cmd]\n";
system($cmd) == 0
    or die "Couldn't run [$cmd]: $!/$?/$^E";
[download]