Well, there is for sure a difference, whether you put this code into Perl, or into the shell. For example, depending on the value of $DEST, Perl might decide to pass on the command to the shell for evaluation, or call tar directly.

In order to discuss this, we would need to know the interpolated string - something like

my $cmd="tar -zcf $filename $DEST 2>&1";
my $cmd_output=`$cmd`;
print "Command $cmd produced the output:\n$cmd_output\n";
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would do.