Good bash script when you want only take part of filename using regexp for renaming
#!/bin/bash
for filename in *.m4a; do
newFilename=$(echo $filename | \
sed -r 's#^(.*) - (.*)-(.*).m4a$#\2.m4a#')
mv "$filename" "$newFilename"
done
Also, you can use rename command
rename s/.mp4$/.m4a/ *.mp4
#!/bin/bash
for filename in *.m4a; do
newFilename=$(echo $filename | \
sed -r 's#^(.*) - (.*)-(.*).m4a$#\2.m4a#')
mv "$filename" "$newFilename"
done
Also, you can use rename command
rename s/.mp4$/.m4a/ *.mp4