1 files changed, 74 insertions, 0 deletions
diff --git a/itches/emacs/interpreters.org b/itches/emacs/interpreters.org
index 43a60d7..478c10a 100644
--- a/itches/emacs/interpreters.org
+++ b/itches/emacs/interpreters.org
@@ -4,6 +4,80 @@
 ** Use Bash completions.
 E.g. in most terminals, typing ~ls TAB~ in a folder with a single file
 expands to ~ls that-file~.
+** Handle DECSC, DECRC, CUU, ED, HVP and DECSTBM console codes.
+Used for APT's "Dpkg::Progress-Fancy" option, enabled by default with
+the high-level apt(8) command.  Silly script emulating what APT does:
+#+begin_src bash
+#!/bin/bash
+
+set -eu
+
+if ! test "${LINES:-}" -a "${COLUMNS:-}"
+then
+    echo Please export LINES and COLUMNS.
+    exit 1
+fi
+
+# Adapted from apt/apt-pkg/install-progress.cc.
+
+backup=$'\e7'                    # DECSC: backup cursor position.
+restore=$'\e8'                   # DECRC: restore cursor position.
+
+setup ()
+{
+    echo -n ${backup}
+    # DECSTBM: restrict scrolling below command, and above progress
+    #          bar.  Side-effect: move the cursor to position 1:1,
+    #          hence the backup/restore.
+    echo -n $'\e[0;'$((LINES-1))'r'
+    echo -n ${restore}
+}
+
+teardown ()
+{
+    # ED: clear everything from current position to end of screen.
+    #     Dixit Michael Vogt: "sledgehammer".
+    echo -n $'\e[J'
+}
+
+# APT surrounds this setup phase with \n and \e[1A (CUU).  I don't
+# know why; the comments say that this is to "avoid visual glitch when
+# the screen area shrinks by one row".  No further explanation is
+# given in commit messages.
+setup
+
+for ((i=1;i<COLUMNS-1;i++))
+do
+    if ! ((i%10))
+    then
+        echo "installing stuff"
+    fi
+
+    echo -n ${backup}
+
+    # HVP: move cursor to last line, first column.
+    echo -n $'\e['${LINES}';1f'
+
+    # Draw progress bar.
+    progress='['
+    for ((j=1;j<=i;j++))
+    do
+        progress+='#'
+    done
+    for ((j=i+1;j<COLUMNS-1;j++))
+    do
+        progress+='.'
+    done
+    progress+=']'
+    echo -n ${progress}
+
+    echo -n ${restore}
+
+    sleep 0.1
+done
+
+teardown
+#+end_src
 * Eshell
 ** ~ls --group-directories-first~ does not color folders.
 * Python shell