Initial version

.gitignore

@@ -0,0 +1 @@
+/missingnewline

LICENSE

@@ -1,6 +1,6 @@
 MIT License
 
-Copyright (c) <year> <copyright holders>
+Copyright (c) 2023 Laurence Withers.
 
 Permission is hereby granted, free of charge, to any person obtaining a copy
 of this software and associated documentation files (the "Software"), to deal

README.md

@@ -1,3 +1,17 @@
 # missingnewline
 
-Prints a "🚫" character and adds a newline if the cursor is not in column 1. You can use it in your shell prompt to tidy up after commands that output some text without a trailing newline.
+Prints a "🚫" character and adds a newline if the cursor is not in column 1.
+You can use it in your shell prompt to tidy up after commands that output some
+text without a trailing newline.
+
+![Example terminal session showing the problem of an unterminated command mixing with the shell prompt, and then the program correctly detecting the presence or absence of a non-newline-terminated output and using the "🚫" character appropriately.](example.gif)
+
+You can install this into your `~/.bashrc`, for example:
+
+```
+declare -a PROMPT_COMMAND
+if [ -x "${HOME}/go/bin/missingnewline" ]
+then
+  PROMPT_COMMAND+=("${HOME}/go/bin/missingnewline")
+fi
+```

go.mod

@@ -0,0 +1,8 @@
+module src.lwithers.me.uk/go/missingnewline
+
+go 1.20
+
+require (
+	golang.org/x/sys v0.7.0
+	golang.org/x/term v0.7.0
+)

go.sum

@@ -0,0 +1,4 @@
+golang.org/x/sys v0.7.0 h1:3jlCCIQZPdOYu1h8BkNvLz8Kgwtae2cagcG/VamtZRU=
+golang.org/x/sys v0.7.0/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
+golang.org/x/term v0.7.0 h1:BEvjmm5fURWqcfbSKTdpkDXYBrUS1c0m8agp14W48vQ=
+golang.org/x/term v0.7.0/go.mod h1:P32HKFT3hSsZrRxla30E9HqToFYAQPCMs/zFMBUFqPY=

main.go

@@ -0,0 +1,106 @@
+package main
+
+import (
+	"bytes"
+	"fmt"
+	"os"
+	"strconv"
+	"strings"
+	"time"
+
+	"golang.org/x/sys/unix"
+	"golang.org/x/term"
+)
+
+func main() {
+	st, err := term.MakeRaw(0)
+	if err != nil {
+		os.Exit(1)
+	}
+
+	var column int
+	select {
+	case <-time.After(100 * time.Millisecond):
+	case column = <-awaitColumn():
+	}
+
+	term.Restore(0, st)
+	if column > 1 {
+		unix.Write(1, []byte("🚫\n")) // U+1F6AB
+	}
+}
+
+func awaitColumn() <-chan int {
+	ch := make(chan int)
+	go func() {
+		row, col := readDSR()
+		_ = row
+		ch <- col
+	}()
+	return ch
+}
+
+func readDSR() (row, col int) {
+	unix.Write(1, []byte{
+		'\033', '[', // ANSI escape code: CSI
+		'6', 'n', // DSR / device status report
+	})
+
+	buf := make([]byte, 64)
+	n, err := unix.Read(0, buf)
+	if err != nil {
+		return 0, 0
+	}
+	buf = buf[:n]
+
+	if len(buf) < 6 || buf[0] != '\033' || buf[1] != '[' || buf[len(buf)-1] != 'R' {
+		return 0, 0
+	}
+
+	s := string(buf[2 : len(buf)-1])
+	pos := strings.IndexByte(s, ';')
+	if pos == -1 {
+		return 0, 0
+	}
+
+	row, err = strconv.Atoi(s[:pos])
+	if err != nil {
+		return 0, 0
+	}
+	col, err = strconv.Atoi(s[pos+1:])
+	if err != nil {
+		return 0, 0
+	}
+	return row, col
+}
+
+func processit(b []byte) {
+	if !bytes.HasPrefix(b, []byte{'\033', '['}) {
+		return
+	}
+	if !bytes.HasSuffix(b, []byte{'R'}) {
+		return
+	}
+	s := string(b[2 : len(b)-1])
+	pos := strings.IndexByte(s, ';')
+	if pos == -1 {
+		return
+	}
+	x, err := strconv.Atoi(s[pos+1:])
+	if err != nil {
+		return
+	}
+	if x != 1 {
+		fmt.Println("🚫") // U+1F6AB
+	}
+}
+
+func readit() chan []byte {
+	q := make(chan []byte)
+	go func() {
+		b := make([]byte, 1024)
+		n, _ := os.Stdin.Read(b)
+		q <- b[:n]
+	}()
+	return q
+}