Shell scripting: Why does only the "-" hyphen throw an error?

Question

Goal: Cleaning up

Selectively truncate filenames in my nvALT notes folder. I tried using a productivity blogger's suggestion (which eludes me after a thorough search) to prepend ^ > - + to filenames, but it's not working for me. It's time to clean house! However, I need to make sure I don't lop off any alpha characters on filenames that do not use those prefixes. Plus I'm learning scripting and think it's fun!

Shell script

Here's what I've got:

#!/bin/bash

cd ~/dropbox/notes_test

for f in *; do
  FILENAME=$(basename "$f")
  DIRNAME=$(dirname "$f")
  if [[ "$f" == \^\ * ]]; then
    mv "$f" "${DIRNAME}/${FILENAME:2}"
  fi
  if [[ "$f" == \+\ * ]]; then
    mv "$f" "${DIRNAME}/${FILENAME:2}"
  fi
  if [[ "$f" == \>\ * ]]; then
    mv "$f" "${DIRNAME}/${FILENAME:2}"
  fi
  if [[ "$f" == \-\ * ]]; then
    mv "$f" "${DIRNAME}/${FILENAME:2}"
  fi
done

Problem: The hyphen

Here's the command line input and error message. I get one of these for each filename beginning with "- ".

DEV0041:scripts n$ ./truncate.sh
basename: illegal option --  
usage: basename string [suffix]
       basename [-a] [-s suffix] string [...]
dirname: illegal option --  
usage: dirname path
mv: illegal option --  
usage: mv [-f | -i | -n] [-v] source target
       mv [-f | -i | -n] [-v] source ... directory

Question: Why does the hyphen—and only the hyphen—throw an error?

And how to work around this issue?

Answer 1

From the man page for mv, the first (and possibly second) argument on the command line, if it begins with a -, is an option and not a file. Only -f | -i | -n are allowed options.

Simplest way is not to use - in a file name—it will confuse other command line programs—given that prepending - is a workaround for something else I would just not use that character.

If this is not an option, you can rewrite the mv commands like this

mv ./"$f" "${DIRNAME}/${FILENAME:2}"

or (a bit more generic because it then also works for absolute paths)

mv -- "$f" "${DIRNAME}/${FILENAME:2}"

Another option (and is what I would do for any bash script longer than a few lines) is write in a scripting language like perl or python - in this case they solve the problem by their move functions not passing the filenames to mv