Script to download sequentially named files, rename them, and delete smaller files

Question

I've written a little script to download sequentially named files, rename them, and delete files smaller than an certain number of kilobytes. I came up with this but I'm not too happy. Any advice for me?

#!/bin/sh
echo
echo -n "Start file #:"
read start
echo
echo -n "End file #:"
read end
echo

wget --progress=bar:force http://www.mybox.com/pictures/show_pic.asp?src_id={$start..$end} 2>&1 | progressfilt

sleep 1

for file in *.asp
do
    mv "$file" "${file%.asp}.jpg"
done

find * -maxdepth 1 -name "*.jpg" -size -300k -delete

echo "tasks completed...exiting"
exit

Answer 1

• sh is not bash. This shouldn't be a problem for your script though, because I don't think there are any bashisms in there.
• Use More Quotes™. If there had been another parameter in the URL you would have needed an ampersand (&) in there, and that's the special character to run a command in the background. That's one of many ways to trip up if you don't comment basically any non-trivial string.
• You don't need to sleep, because the wget commands are synchronous.
• That said, you might get a result much faster if you run them in parallel, by doing several wget […] & commands followed by a wait.
• You don't need to exit at the end of a shell script. That's only useful if you want to exit prematurely or with a different exit code from the previous command.
• If you use Bash you can use read -p "Start file #: " start etc. to avoid most of the echoing.

• However, it is much more common to make shell scripts take parameters instead of being interactive, making the script even simpler:

  start="$1"
  end="$2"
  

• Use set -o errexit -o nounset (and -o pipefail if you're really in Bash) to make sure you catch any common bugs early.
• I'm not sure what progressfilt does, but you can suppress the wget progress bar by using --quiet.
• To be done slightly faster you should swap around the deleting and the renaming.
• Rather than find * you should use find . to avoid exceeding the maximum argument length. This is a good practice in general, but will only really break with lots of files.
• One very common feature of *nix scripts is that they are silent unless there's something important to report. Therefore, I'd remove the last echo.

Your script should now be 9 SLOC, and clean as a whistle!