Document what the backtick returns if the command fails.

p4raw-id: //depot/perl@6682

diff --git a/pod/perlop.pod b/pod/perlop.pod
index 0f83ed1..9b4dbaf 100644 (file)
--- a/pod/perlop.pod
+++ b/pod/perlop.pod
@@ -997,13 +997,14 @@ for a detailed look at the semantics of regular expressions.
 
 =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.