Index: texinfo-7.1/tp/Texinfo/Convert/DocBook.pm
===================================================================
--- texinfo-7.1.orig/tp/Texinfo/Convert/DocBook.pm
+++ texinfo-7.1/tp/Texinfo/Convert/DocBook.pm
@@ -340,7 +340,7 @@ sub output($$)
 
   my $fh;
   my $encoded_output_file;
-  if (! $output_file eq '') {
+  if ($output_file ne '') {
     my $path_encoding;
     ($encoded_output_file, $path_encoding)
       = $self->encoded_output_file_name($output_file);
Index: texinfo-7.1/tp/Texinfo/Convert/Info.pm
===================================================================
--- texinfo-7.1.orig/tp/Texinfo/Convert/Info.pm
+++ texinfo-7.1/tp/Texinfo/Convert/Info.pm
@@ -100,7 +100,7 @@ sub output($)
   my $tree_units = Texinfo::Structuring::split_by_node($root);
 
   my $fh;
-  if (! $output_file eq '') {
+  if ($output_file ne '') {
     if ($self->get_conf('VERBOSE')) {
       print STDERR "Output file $output_file\n";
     }
Index: texinfo-7.1/tp/Texinfo/Convert/LaTeX.pm
===================================================================
--- texinfo-7.1.orig/tp/Texinfo/Convert/LaTeX.pm
+++ texinfo-7.1/tp/Texinfo/Convert/LaTeX.pm
@@ -1065,7 +1065,7 @@ sub output($$)
 
   my $fh;
   my $encoded_output_file;
-  if (! $output_file eq '') {
+  if ($output_file ne '') {
     my $path_encoding;
     ($encoded_output_file, $path_encoding)
       = $self->encoded_output_file_name($output_file);
Index: texinfo-7.1/tp/Texinfo/Convert/TexinfoMarkup.pm
===================================================================
--- texinfo-7.1.orig/tp/Texinfo/Convert/TexinfoMarkup.pm
+++ texinfo-7.1/tp/Texinfo/Convert/TexinfoMarkup.pm
@@ -298,7 +298,7 @@ sub output($$)
 
   my $fh;
   my $encoded_output_file;
-  if (! $output_file eq '') {
+  if ($output_file ne '') {
     my $path_encoding;
     ($encoded_output_file, $path_encoding)
       = $self->encoded_output_file_name($output_file);