Add preview.sh for ruby-less previews. (#259)

bin/preview.sh

@@ -0,0 +1,44 @@
+#!/bin/bash
+
+REVERSE="\x1b[7m"
+RESET="\x1b[m"
+
+if [ "$1" == "-v" ]; then
+    SPLIT=1
+    shift
+fi
+
+if [ -z "$1" ]; then
+    echo "usage: $0 [-v] FILENAME[:LINENO][:IGNORED]"
+    exit 1
+fi
+
+IFS=':' read -r -a INPUT <<< "$1"
+FILE=${INPUT[0]}
+CENTER=${INPUT[1]}
+
+if [ ! -r "$FILE" ]; then
+    echo "File not found ${FILE}"
+    exit 1
+fi
+
+if [ -z "$CENTER" ]; then
+    CENTER=1
+fi
+
+if [ -r /dev/tty ]; then
+    LINES=$(stty size < /dev/tty | awk '{print $1}')
+else
+    LINES=40
+fi
+
+if [ -n "$SPLIT" ]; then
+    LINES=$(($LINES/2)) # using horizontal split
+fi
+LINES=$(($LINES-2)) # remove preview border
+
+FIRST=$(($CENTER-$LINES/3))
+FIRST=$(($FIRST < 1 ? 1 : $FIRST))
+LAST=$((${FIRST}+${LINES}-1))
+
+awk "NR >= $FIRST && NR <= $LAST {if (NR == $CENTER) printf(\"\x1b[7m%5d %s\n\x1b[m\", NR, \$0); else printf(\"%5d %s\n\", NR, \$0)}" $FILE