How to store NUL output of a program in bash script?

Question

Suppose there is a directory 'foo' which contains several files:

ls foo:
1.aa 2.bb 3.aa 4.cc

Now in a bash script, I want to count the number of files with specific suffix in 'foo', and display them, e.g.:

SUFF='aa'
FILES=`ls -1 *."$SUFF" foo`
COUNT=`echo $FILES | wc -l`
echo "$COUNT files have suffix $SUFF, they are: $FILES"

The problem is: if SUFF='dd', $COUNT also equal to 1. After google, the reason I found is when SUFF='dd', $FILES is an empty string, not really the null output of a program, which will be considered to have one line by wc. NUL output can only be passed through pipes. So one solution is:

COUNT=`ls -1 *."$SUFF" foo | wc -l`

but this will lead to the ls command being executed twice. So my question is: is there any more elegant way to achieve this?

Answer 1

$ shopt -s nullglob
$ FILES=(*)
$ echo "${#FILES[@]}"
4
$ FILES=(*aa)
$ echo "${#FILES[@]}"
2
$ FILES=(*dd)
$ echo "${#FILES[@]}"
0
$ SUFFIX=aa
$ FILES=(*"$SUFFIX")
$ echo "${#FILES[@]}"
2
$ SUFFIX=dd
$ FILES=(*"$SUFFIX")
$ echo "${#FILES[@]}"
0