add ruler mode to pagetest.sh for exact chars-per-line calibration

Repeating-digit and prefixed-number test lines make it hard to read
off exactly where a printer truncates a line. `./pagetest.sh ruler`
prints a single line marking every 10th column with its tens digit
and every 5th with '+', so the real cutoff column can be read directly
off the page instead of estimated.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

pagetest.sh

@@ -1,34 +1,58 @@
 #!/bin/bash
 #
-# Generates a page-break diagnostic file: numbered lines padded with '#' to
-# a fixed width, so you can see exactly where a printer's real page length
-# and line width limits are instead of guessing from paper geometry.
+# Generates printer diagnostic files, so you can read a printer's real page
+# capacity straight off the paper instead of guessing from paper geometry.
 #
-# Usage: ./pagetest.sh [width] [lines]
-#   width - characters per line, including the "NNN " prefix (default 64)
-#   lines - number of lines to generate (default 100)
+# Usage:
+#   ./pagetest.sh [width] [lines]   - numbered lines padded with '#', to find
+#                                      a printer's real lines-per-page (the
+#                                      last line number printed on page 1)
+#                                      (default width=64, lines=100)
+#   ./pagetest.sh ruler [width]     - a single long ruler line marking every
+#                                      10th column with its tens digit and
+#                                      every 5th with '+', to find a
+#                                      printer's real chars-per-line exactly
+#                                      (default width=200)
 #
-# Print the result with PRINTER_A4=false in printer.conf (no rotation), so
-# the line numbers read straight off the page:
+# Print the result with PRINTER_A4=false in printer.conf (no rotation):
 #   ./txt2printr.sh pagetest.txt
 
 dir="$(dirname "$0")"
-width="${1:-64}"
-lines="${2:-100}"
 outfile="$dir/pagetest.txt"
 
-awk -v width="$width" -v lines="$lines" '
-    BEGIN {
-        for (i = 1; i <= lines; i++) {
-            prefix = sprintf("%03d ", i)
-            fill = width - length(prefix)
-            if (fill < 0) fill = 0
-            line = prefix
-            for (j = 0; j < fill; j++) line = line "#"
+if [ "$1" = "ruler" ]; then
+    width="${2:-200}"
+    awk -v width="$width" '
+        BEGIN {
+            line = ""
+            for (i = 1; i <= width; i++) {
+                if (i % 10 == 0) line = line (int(i / 10) % 10)
+                else if (i % 5 == 0) line = line "+"
+                else line = line "-"
+            }
             print line
         }
-    }
-' > "$outfile"
+    ' > "$outfile"
+    echo "Wrote a $width-char ruler line to $outfile"
+    echo "Every 10th column is marked with its tens digit (column 40 -> '4',"
+    echo "column 100 -> '0'), every 5th with '+'. Read off the last marker"
+    echo "that fully prints to get your printer's exact chars-per-line."
+else
+    width="${1:-64}"
+    lines="${2:-100}"
+    awk -v width="$width" -v lines="$lines" '
+        BEGIN {
+            for (i = 1; i <= lines; i++) {
+                prefix = sprintf("%03d ", i)
+                fill = width - length(prefix)
+                if (fill < 0) fill = 0
+                line = prefix
+                for (j = 0; j < fill; j++) line = line "#"
+                print line
+            }
+        }
+    ' > "$outfile"
+    echo "Wrote $lines lines x $width chars to $outfile"
+fi
 
-echo "Wrote $lines lines x $width chars to $outfile"
 echo "Print it with: PRINTER_DEV=/dev/lp0 \"$dir/txt2printr.sh\" \"$outfile\""