linux - Bash: how to know if the last command's output ends with a newline or not?

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Most of the time the output of a
command ends with the newline character. But sometimes it does not, so the next shell
prompt is printed in the same line together with the
output.

Example:

root@hostname [~] # echo -n hello
helloroot@hostname [~]
#

I've always
found that very annoying.
Now, I could just add a "\n" at the beginning of
the the PS1 variable, but most of the time that will print one extra line I dont
need.

Is it possible to know whether the last
command's output ended with a newline or
not?

/>

Solution: />(Thanks to
Dennis)

PS1='$(printf "%$((`tput
            cols`-1))s\r")\u@\h [\w]\$ '

Answer

I've been experimenting with the following to emulate the feature from
zsh in
Bash:

$ unset PROMPT_SP; for ((i =
            1; i <= $COLUMNS + 52; i++ )); do PROMPT_SP+=' '; done

$
            PS1='\[\e[7m%\e[m\]${PROMPT_SP: -$COLUMNS+1}\015$
            '

It issues a reverse
video percent sign, followed by a bunch of spaces to make it wrap to the next line, then
a carriage return, followed by a dollar sign and a space. You can add prompt escapes
after the "\015" to customize your prompt.

Using
this depends on how your terminal handles right margin line wrapping (automatic
margins). The length of PROMPT_SP is arbitrary, but should be at least 80 or whatever
your usual terminal width is. You may need to hard-code that value if $COLUMNS isn't set
yet by the time the for loop is run in
~/.bashrc. You may want shopt -s
checkwinsize if it's not already set.