Subject: bug#35129: Unsupported escape sequences for progress in shell

From: Juri Linkov <[email-masked]>
Date: Wed, 03 Apr 2019 23:27:24 +0300

Some escape sequences are unhandled in shell mode.
Most often they appear when running `apt install'
that shows its progress bar that is supposed to stay
on the same line, but spreads over several lines,
so the output looks like a mess (where ^[7 and ^[8
are escape sequences currently still unhandled):

  debconf: unable to initialize frontend: Dialog
  debconf: (Dialog frontend will not work on a dumb terminal, an emacs shell buffer, or without a controlling terminal.)
  debconf: falling back to frontend: Readline
  ^[7Progress: [  0%] [................................................................................................] ^[8
  ^[7Progress: [  6%] [######..........................................................................................] ^[8
  ^[7Progress: [ 13%] [############....................................................................................] ^[8
  ^[7Progress: [ 19%] [##################..............................................................................] ^[8
  ^[7Progress: [ 25%] [########################........................................................................] ^[8
  ^[7Progress: [ 31%] [##############################..................................................................] ^[8
  ^[7Progress: [ 38%] [####################################............................................................] ^[8
  ^[7Progress: [ 44%] [##########################################......................................................] ^[8
  ^[7Progress: [ 50%] [################################################................................................] ^[8
  ^[7Progress: [ 56%] [######################################################..........................................] ^[8
  ^[7Progress: [ 63%] [############################################################....................................] ^[8
  ^[7Progress: [ 69%] [##################################################################..............................] ^[8
  ^[7Progress: [ 75%] [########################################################################........................] ^[8
  ^[7Progress: [ 81%] [##############################################################################..................] ^[8
  ^[7Progress: [ 88%] [####################################################################################............] ^[8
  ^[7Progress: [ 94%] [##########################################################################################......] ^[8

I'm making this report because escape sequences for colors are handled fine,
and visually these indicators have the green background.