Add a newline only if it doesn't exist

Question

I want to add a newline at the end of a file only if it doesn\'t exists, this is to prevent multiple newlines at the end of the file.

I\'m hoping to use sed. Here\'s the

Answer 1

Rather than processing the whole file with see just to add a newline at the end, just check the last character and if it's not a newline, append one. Testing for newline is slightly interesting, since the shell will generally trim them from the end of strings, so I append "x" to protect it:

if [ "$(tail -c1 "$inputfile"; echo x)" != $'\nx' ]; then
    echo "" >>"$inputfile"
fi

Note that this will append newline to empty files, which might not be what you want. If you want to leave empty files alone, add another test:

if [ -s "$inputfile" ] && [ "$(tail -c1 "$inputfile"; echo x)" != $'\nx' ]; then
    echo "" >>"$inputfile"
fi