1 files changed, 170 insertions, 0 deletions

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+#!/bin/sh
+
+# https://unix.stackexchange.com/a/464963
+readc() { # arg: <variable-name>
+        if [ -t 0 ]; then
+                # if stdin is a tty device, put it out of icanon, set min and
+                # time to sane value, but don't otherwise touch other input or
+                # or local settings (echo, isig, icrnl...). Take a backup of the
+                # previous settings beforehand.
+                saved_tty_settings=$(stty -g)
+                stty -icanon min 1 time 0
+        fi
+        eval "$1="
+        while
+                # read one byte, using a work around for the fact that command
+                # substitution strips the last character.
+                c=$(dd bs=1 count=1 2> /dev/null; echo .)
+                c=${c%.}
+
+                # break out of the loop on empty input (eof) or if a full character
+                # has been accumulated in the output variable (using "wc -m" to count
+                # the number of characters).
+                [ -n "$c" ] &&
+                        eval "$1=\${$1}"'$c
+          [ "$(($(printf %s "${'"$1"'}" | wc -m)))" -eq 0 ]'; do
+                continue
+        done
+        if [ -t 0 ]; then
+                # restore settings saved earlier if stdin is a tty device.
+                stty "$saved_tty_settings"
+        fi
+}
+
+setup_terminal() {
+        # Setup the terminal for the TUI.
+        # '\e[?1049h': Use alternative screen buffer.
+        # '\e[?7l':    Disable line wrapping.
+        # '\e[?25l':   Hide the cursor.
+        # '\e[2J':     Clear the screen.
+        # '\e[1;Nr':   Limit scrolling to scrolling area.
+        #              Also sets cursor to (0,0).
+        printf '\e[?1049h\e[?7l\e[2J\e[1;%sr' "$((LINES - 1))"
+
+        # Hide echoing of user input
+        stty -echo
+}
+
+reset_terminal() {
+        # Reset the terminal to a useable state (undo all changes).
+        # '\e[?7h':   Re-enable line wrapping.
+        # '\e[?25h':  Unhide the cursor.
+        # '\e[2J':    Clear the terminal.
+        # '\e[;r':    Set the scroll region to its default value.
+        #             Also sets cursor to (0,0).
+        # '\e[?1049l: Restore main screen buffer.
+        printf '\e[?7h\e[?25h\e[2J\e[;r\e[?1049l'
+
+        # Show user input.
+        stty echo
+}
+
+printlines() { # printlines file min max
+        if test -n "$DEBUG"; then
+                echo --- >&2
+        else
+                clear
+        fi
+        sed -n "$2,$3p" "$1"
+        notify_flush
+}
+
+notify() { # notify STRING
+        notification="$notification$1"
+}
+
+notify_flush() { # notify_flush
+        winch
+        printf '\e[s\e[%s;%sH' 0 "$c"
+        printf '%s' "$notification"
+        printf '\e[u'
+        notification=
+}
+
+scroll() { # scroll nlines -- MUTATES GLOBAL STATE
+        case "${1:-0}" in
+                \+*|\-*) n=$((n+$1)) ;;
+                0) ;;
+                *) n=$1 ;;
+        esac
+
+        if test $n -gt $((max - l))
+        then
+                n=$((max - l))
+                notify '_'
+        fi
+
+        if test $n -lt $min
+        then
+                notify '^'
+                n=$min
+        fi
+
+        m=$((n+l))
+        if $m -ge $max
+        then
+                m=$max
+        fi
+        # echo "min:$min max:$max n:$n m:$m l:$l" >&2
+}
+
+ctty() { # ctty
+        ## Get the controlling TTY interface.
+        tty <&2 || # only works if not redirecting stderr
+                echo /proc/self/fd/1 # probably only works on linux
+}
+
+winch() {
+        stty size > "$wf"
+        read -r l c < "$wf"
+        # echo l:$l c:$c >&2
+        l=$((l-2)) # last line
+}
+
+cleanup() {
+        rm "$bf" "$wf"
+        reset_terminal
+        exit
+}
+
+vellum() { # vellum [-n NUM] < INPUT
+        # Set up buffer
+        bf="$(mktemp)" # buffer
+        cat "${@:--}" > "$bf"
+        # Redirect input to the controlling terminal
+        ## XXX: This assumes that you haven't redirected stderr.
+        exec < "$(ctty)"
+        max=$(wc -l < "$bf")
+        min=1 # min = minimum accessible line num.
+        n=$min # n = num. first line to show
+
+        # Set up terminal
+        setup_terminal
+        wf="$(mktemp)" # winch file
+        winch; trap winch WINCH
+        m=$((n+l)) # m = num. last line to show
+
+        trap cleanup EXIT INT QUIT
+
+        # Main loop
+        while :; do
+                scroll
+                printlines "$bf" $n $m
+
+                readc key >/dev/null 2>&1
+                case "$key" in
+                        ' ') scroll +$l ;;
+                        '') scroll -$l ;;
+                        j) scroll +1 ;;
+                        k) scroll -1 ;;
+                        g) scroll $min ;;
+                        G) scroll $max ;;
+                        q) break ;;
+                esac
+        done
+        break
+        echo
+}
+
+test -n "$DEBUG" && { set -x; exec 2> /tmp/vellum.log; }
+test -z "$SOURCE" && vellum "$@"