Question

Is it possible to get the output of a command – for example tar – to write each line of output to one line only?

Example usage:

tar -options -f dest source | [insert trickery here]

and the output would show every file being processed without making the screen move: each output overwrites the last one. Can it be done?

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Edit: we seem to have a working answer, but lets take it further:
How about doing the same, but over 5 lines? You see a scrolling output that doesn’t affect the rest of the terminal. I think I’ve got an answer, but I’d like to see what you guys think.

Answer 1

Replace the newlines with carriage returns.

 tar -options -f dest source | cut -b1-$(tput cols) | sed -u 'i\\o033[2K' | stdbuf -o0 tr '\n' '\r'; echo

Explanation:

• cut -b1-$(tput cols): Truncates the output of tar if it is longer than the terminal is wide. Depending on how little you want your terminal to move, it isn’t strictly necessary.

• sed -u 'i\\o033[2K': Inserts a line blank at the beginning of each line. The -u option to sed puts it in unbuffered mode. stdbuf -oL sed 'i\\033[2K' would work equally as well.

• stdbuf -o0 tr '\n' '\r': Uses tr to exchange newlines with carriage returns. Stdbuf makes sure that the output is unbuffered; without the \n‘s, on a line buffered terminal, we’d see no output.

• echo: Outputs a final newline, so that the terminal prompt doesn’t eat up the final line.

For the problem your edit proposes:

x=0; 
echo -e '\e[s'; 
tar -options -f dest source | while read line; do
      echo -en "\e[u" 
      if [ $x gt 0 ]; then echo -en "\e["$x"B"; fi;
      echo -en "\e[2K"
      echo -n $line | cut -b1-$(tput cols);
      let "x = ($x+1)%5";
done; echo;

Feel free to smush all that onto one line. This actually yields an alternative solution for the original problem:

echo -e '\e[s'; tar -options -f dest source | while read line; do echo -en "\e[u\e2K"; echo -n $line | cut -b1-$(tput cols); done; echo

which neatly relies on nothing except VT100 codes.