Bash check whether my asterisk expansion has any matches - regex

Question

I use the following code to search for matching files in the current directory:
# Check for existing backups
EXISTINGFILES="./dropbox-backup-*.tar.gz"
if [[ ! -z "$EXISTINGFILES" ]]
then
echo "Found existing backups!"
# do stuff here...
else
echo "Did not find any existing backups."
fi
This method for finding matching files allows me to iterate over matches with a loop such as for f in $EXISTINGFILES, but it never detects when no matching files were found.
How can I modify my code above to detect when no matching files were found??

Answer 1

Use this instead:
EXISTINGFILES=`find . -type f -name 'dropbox-backup-*.tar.gz'`
Explanation:
The problem with EXISTINGFILES=./dropbox-backup-*.tar.gz, in the context of your script, is that $EXISTINGFILES will always be non-zero since you are assigning it a value ("./dropbox-backup-*.tar.gz").
In the above solution, we are first finding the file(s) and assigning it to the variable. If the file is not found, then the variable will be zero and your script will go to the else block (i.e. will indicate "no matching files were found").

Answer 2

You seem to be looking for nullglob. Say:
shopt -s nullglob
at the top of your script.
$ ls foobar*
ls: foobar*: No such file or directory
$ for i in foobar*; do echo $i; done # Print foobar* if doesn't find match
foobar*
$ shopt -s nullglob
$ for i in foobar*; do echo $i; done # Doesn't print anything if no match found
$

Answer 3

Turn existing_files into bash array and also use nullglob
shopt -s nullglob
existing_files=(./dropbox-backup-*.tar.gz)
if ((${#existing_files[#]})); then echo 'files exist'; fi

Answer 4

The problem is that you are quoting the asterisk both when you set the value of EXISTINGFILES and when you expand it, so that it is never treated as a wild-card pattern. I would skip the use of variable and use the pattern by itself like this:
for f in ./dropbox-backup-*.tar.gz; do
if [[ -f "$f" ]]; then
echo "Found existing backups!"
# do stuff here...
else
echo "Did not find any existing backups."
fi
break
done
If you want to store the full list of matching names, use an array:
EXISTINGFILES=( ./dropbox-backup-*.tar.gz )
if [[ -f "${EXISTINGFILES[0]}" ]]; then
By default, a pattern that matches 0 files is treated literally, which is why I use -f in the above examples: to test if the "file" (which might be the literal pattern instead) actually exists. You can modify the default behavior so that a non-matching pattern simply vanishes instead:
shopt -s nullglob
EXISTINGFILES=( ./dropbox-backup-*.tar.gz )
for f in "${EXISTINGFILES[#]}"; do
# Do stuff; there is at least one matching file if we are in
# the body of the loop
done