From 50142e9bbcfc2ab2c83c99bae5669cf606c47014 Mon Sep 17 00:00:00 2001
From: Case Duckworth
Date: Wed, 8 Mar 2023 14:14:51 -0600
Subject: Fix arithmetic error in scroll causing crash

---
 vellum | 18 ++++++++++++------
 1 file changed, 12 insertions(+), 6 deletions(-)

diff --git a/vellum b/vellum
index aee12d5..8cd03c2 100755
--- a/vellum
+++ b/vellum
@@ -1,8 +1,8 @@
-#!/bin/sh
+set +x
 
 readc() { # arg: <variable-name>
 	# adapted from https://unix.stackexchange.com/a/464963
-	if [ -t 0 ]; then
+	if test -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
@@ -97,8 +97,9 @@ notify_flush() { # notify_flush
 }
 
 scroll() { # scroll nlines -- MUTATES GLOBAL STATE
-	case "${1:-0}" in
-		\+*|\-*) n=$((n+$1)) ;;
+	arg="${1:-0}"
+	case "$arg" in
+		+*|-*) n=$((n+${arg#+})) ;;
 		0) ;;
 		*) n=$1 ;;
 	esac
@@ -116,7 +117,7 @@ scroll() { # scroll nlines -- MUTATES GLOBAL STATE
 	fi
 
 	m=$((n+l))
-	if $m -ge $max
+	if test $m -ge $max
 	then
 		m=$max
 	fi
@@ -125,8 +126,13 @@ scroll() { # scroll nlines -- MUTATES GLOBAL STATE
 
 ctty() { # ctty
 	## Get the controlling TTY interface.
-	tty <&2 || # only works if not redirecting stderr
+	if test -t 2
+	then
+		# only works if not redirecting stderr
+		tty <&2
+	else
 		echo /proc/self/fd/1 # probably only works on linux
+	fi
 }
 
 winch() {
-- 
cgit 1.4.1-21-gabe81