Using the output of if statement (cmp) in a cp command

I am trying to use the output of an if statement as input for a cp command, but it does not seem to work. My code is:

for fname in $(find $1 -name "IMG_[0-9][0-9][0-9][0-9].JPG")
do
  filename=$(basename $fname)
  if cmp $2/$filename $fname; then 
    cp $fname $2/$filename.JPG
  fi

the output I am getting is

lel//IMG_0039.JPG dir/dir2/IMG_0039.JPG differ: byte 212, line 1 
lel//IMG_2317.JPG dir/dir/IMG_2317.JPG differ: byte 212, line 1

and I want to copy only those two files while giving them .JPG suffix, so they don't overwrite the existing ones in $2, however it copies all the files in folder $1 to folder $2, while giving them the .JPG suffix, so now instead of having copy of the different one I have copies of the same files only that they have suffix .JPG

I think the cp statement is incorrect, as the cmp only gives the difference between the files and then executes the cp if there is a difference. I already copied the files with a for loop, now I am trying to rename and copy the different ones that have same names with the same for but with if statement.

Solution

You don't actually care about the output of cmp, only its exit status. If the exit status is non-zero, then the files differ and you presumably want to do the copy. Also, don't bother with find here.

shopt -s globstar
for source in "$1"/**/IMG_[0-9][0-9][0-9][0-9].JPG; do
   filename=$(basename "$source")
   target="$2/$filename"
   if ! cmp -s "$source" "$target"; then
       cp "$source" "$target"
   fi
   # cmp -s "$source" "$target" || cp "$source" "$target"
done

The ! negates the exit status, as if executes the body if the condition has a zero exit status. Since you want to execute when cmp has a nonzero exit status, we negate it first.

Be sure to quote all your parameter expansions. Leaving them unquoted will break your code if you happen to have a file name like $1/more files/IMG_9342.JPG.