Ubuntu – How to start multi-threading multiple processes with one command

You missed do after for ... string. Here is a slightly modified script, but your version will work also if you add do missing in there.

for f in *.png
  do
  echo "Converting $f."
  convert "$f" -resize 80% "${f/.png/-80%.png}"
done

A name changing here works as follows: for every $f as a text string find its .png part and change it for -80%.png

The problem is in your line 120. You are right there is a missing '"' and you should add it there.

When you add the '"' at the end of line 120 then line 120 alters your PATH environment variable in a way it shouldn't. It overrides the PATH and does not take care about previous value of PATH. The correct line 120 would be:

export PATH="/home/chill/android-studio/bin:$PATH"

Take a look at other similar lines and you will notice there is always ":$PATH" at the end. That means that you only add a new directory to already existing list of directories in the $PATH. Your line 120 just overrides PATH with one directory. With $PATH at the end your sudo will work too. Not just the bashrc script.