Bash script is printing wrong characters in my variable

Question

I'm trying out the following thing in my terminal:

spark 0 76 100 | awk '{print substr($0,4,3)}'

outputs:

▆

If I do:

GRAPH=$(spark 0 25 100 | awk '{print substr($0,4,3)}')
printf "%s" $GRAPH

I get:

▂%

But looks more like:

As you can see, the % appears to be inside a black bar...

How can I get it to print out:

▂

Without the unexpected % in the same line?

Answer 1

The short answer is to do

printf "%s\n" $GRAPH

When you capture the output from a command into a shell variable with $(…) or `…`, the last newline is stripped, and printf "%s" … (unlike echo) does not append a newline by default.  So, when you say printf "%s" $GRAPH, you are getting the next shell prompt on the same line as your printf output.

Secondly, I advise you to change that to

printf "%s\n" "$GRAPH"

to protect against certain funny characters showing up in $GRAPH –– and you are clearly getting funny characters.

Thirdly, you say, “the % appears to be inside a black bar”.  That appears to be inverse video, in which foreground and background colors are reversed.  That may be caused by one or some of the characters in $GRAPH.  If everything else you do until the end of time is in inverse video, even after you’ve done the above two steps, try

printf "%s\n" "$GRAPH"; tput sgr0

tput exercises terminal-specific functionality; in many cases by writing a string.  sgr0 is the short name for the exit_attribute_mode capability, which sets foreground and background colors back to normal (and turns off underline, blink, and whatever other display attributes your terminal supports).