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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 "$SOURCE" && vellum "$@"
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