Programmatically convert multiple midi files to wave using timidity, ffmpeg, and bash - bash

Question

I am trying to build a script to do as the title says, but I am somewhat unfamiliar with Bash and other online resources have only been so helpful.
#! /bin/bash
function inout #Create Function inout
{
output[0]=" " #Initialize variables
input[0]=" "
count=1
while [ "$count" -lt 10 ]; #Start loop to get all filenames
do
echo "Grabbing filename" #User feedback
input=$(ls | grep 0$count | grep MID | sed 's/ /\\ /g') #Grab filename
#Replace ' ' character with '\ '
output=$(echo $input | tr 'MID' 'mp3')
#set output filename
echo $count #Output variables for testing
echo $input
echo $output
let count+=1 #Increment counter
echo "converting $input to $output." #User feedback
foo="timidity $input -Ow -o - | ffmpeg -i - -acodec libmp3lame -ab 320k $output"
echo $foo
#The last two lines are for the purpose of testing the full output
#I can get the program to run if I copy and paste the output from above
#but if I run it directly with the script it fails
done
}
inout
I am trying to figure out why I can't just run it from inside the script, and why I must copy/paste the output of $foo
Any ideas?

Answer 1

It's impossible to tell from your code how the input files are named; I'll assume something like song_02.MID:
inout () {
for input in song_*.MID; do
output=${input%.MID}.mp3
timidity "$input" -Ow -o - | ffmpeg -i - -acodec libmp3lame -ab 320k "$output"
done
}
They key is to define an appropriate pattern to match your input files, then iterate over the matching files with a for loop.
Also, your use of tr is incorrect: that call would replace any occurrence of M, I, or D with m, p, and 3, respectively; it does not replace occurrences of the 3-character string MID with mp3.