Bash script for re-encode file if re-encoded file does not already exist for all in directory

I have a bash script that takes 1 argument (a file) and runs an ffmpeg command to create a duplicate of the file encoded with a different codec.

#!/bin/bash

ffmpeg -i "$1" -vn -acodec aac "$(basename "${1/.wav}").aac"

I just want to modify this bash script so instead of taking an argument, it instead just checks for all files in the directory to see if the re-encoded file already exists, and if it does not, creates it. Does anyone know how to do this?

Thanks for your help

EDIT: the solution below is working with slight modification:

#!/bin/bash

for file in ./*.wav; do
    [ -e "$file" ] || continue # check if any file exists
    if [[ ! -f "${file}.aac" ]]; then
       ffmpeg -i "${file}" -vn -acodec aac "$(basename "${file}").aac"
    fi;
done;

Solution

Assuming you just want to process all files ending in "*.wav" in a directory. In your bash script you can use find like find . -type f -name "*.wav" and or ls with grep like ls -1 | grep "*.wav" to get the specific codec file names. Then you combine this with something like sed or cut to drop the file extensions and just check if the same file exists with the different codec for each file name. In this case, for example, you can modify your script to:

#!/bin/bash

for file in $(ls -1 | grep ".wav" | sed -e 's/\.wav$//'); do
  if [[ ! -f "${file}.aac" ]]; then
    ffmpeg -i "$file" -vn -acodec aac "$(basename "${file/.wav}").aac"
  fi;
done;

This will create the file with the different codec if it does not exist.

Edit:

From the feedback received in the comments, I think a better answer would be using globbing to allow the shell to expand patterns into a list of matching filenames like this:

#!/bin/bash

for file in ./*.wav; do
    [ -e "$file" ] || continue # check if any file exists
    if [[ ! -f "${file%????}.aac" ]]; then
       ffmpeg -i "${file%????}" -vn -acodec aac "$(basename "${file}").aac"
    fi;
done;