fish: Implement progress bars in guestfish.

The progress bar is updated 3 times per second, and is not displayed
at all for operations which take less than two seconds.

You can disable progress bars by using the flag --no-progress-bars,
and you can enable progress bars in non-interactive sessions with
the flag --progress-bars.

A good way to test this is to use the following command:

guestfish --progress-bars \
          -N disk:10G \
          zero-device /dev/sda

(adjust "10G" to get different lengths of time).

1 files changed, 36 insertions, 0 deletions

diff --git a/fish/guestfish.pod b/fish/guestfish.pod
index cf1140a5..3b9aa203 100644
--- a/fish/guestfish.pod
+++ b/fish/guestfish.pod
@@ -232,6 +232,17 @@ alternative to the I<-a> option: whereas I<-a> adds an existing disk,
 I<-N> creates a preformatted disk with a filesystem and adds it.
 See L</PREPARED DISK IMAGES> below.
 
+=item B<--progress-bars>
+
+Enable progress bars, even when guestfish is used non-interactively.
+
+Progress bars are enabled by default when guestfish is used as an
+interactive shell.
+
+=item B<--no-progress-bars>
+
+Disable progress bars.
+
 =item B<--remote[=pid]>
 
 Send remote commands to C<$GUESTFISH_PID> or C<pid>.  See section
@@ -729,6 +740,31 @@ Create a blank 200MB disk:
 
  guestfish -N disk:200M
 
+=head1 PROGRESS BARS
+
+Some (not all) long-running commands send progress notification
+messages as they are running.  Guestfish turns these messages into
+progress bars.
+
+When a command that supports progress bars takes longer than two
+seconds to run, and if progress bars are enabled, then you will see
+one appearing below the command:
+
+ ><fs> copy-size /large-file /another-file 2048M
+ / 10% [#####-----------------------------------------] 00:30
+
+The spinner on the left hand side moves round once for every progress
+notification received from the backend.  This is a (reasonably) golden
+assurance that the command is "doing something" even if the progress
+bar is not moving, because the command is able to send the progress
+notifications.  When the bar reaches 100% and the command finishes,
+the spinner disappears.
+
+Progress bars are enabled by default when guestfish is used
+interactively.  You can enable them even for non-interactive modes
+using I<--progress-bars>, and you can disable them completely using
+I<--no-progress-bars>.
+
 =head1 GUESTFISH COMMANDS
 
 The commands in this section are guestfish convenience commands, in