Binary "<=>" returns -1, 0, or 1 depending on whether the left
argument is numerically less than, equal to, or greater than the right
-argument.
+argument. If your platform supports NaNs (not-a-numbers) as numeric
+values, using them with "<=>" (or any other numeric comparison)
+returns undef.
Binary "eq" returns true if the left argument is stringwise equal to
the right argument.
Binary "ne" returns true if the left argument is stringwise not equal
to the right argument.
-Binary "cmp" returns -1, 0, or 1 depending on whether the left argument is stringwise
-less than, equal to, or greater than the right argument.
+Binary "cmp" returns -1, 0, or 1 depending on whether the left
+argument is stringwise less than, equal to, or greater than the right
+argument.
"lt", "le", "ge", "gt" and "cmp" use the collation (sort) order specified
by the current locale if C<use locale> is in effect. See L<perllocale>.
=item `STRING`
-A string which is (possibly) interpolated and then executed as a system
-command with C</bin/sh> or its equivalent. Shell wildcards, pipes,
-and redirections will be honored. The collected standard output of the
-command is returned; standard error is unaffected. In scalar context,
-it comes back as a single (potentially multi-line) string. In list
-context, returns a list of lines (however you've defined lines with $/
-or $INPUT_RECORD_SEPARATOR).
+A string which is (possibly) interpolated and then executed as a
+system command with C</bin/sh> or its equivalent. Shell wildcards,
+pipes, and redirections will be honored. The collected standard
+output of the command is returned; standard error is unaffected. In
+scalar context, it comes back as a single (potentially multi-line)
+string, or undef if the command failed. In list context, returns a
+list of lines (however you've defined lines with $/ or
+$INPUT_RECORD_SEPARATOR), or an empty list if the command failed.
Because backticks do not affect standard error, use shell file descriptor
syntax (assuming the shell supports this) if you care to address this.