Unix check if a file exists

test -f yourFile

FILE=/folder/yourFile
if [ -f "$FILE" ]; then
    echo "$FILE exists."
else 
    echo "$FILE does not exist."
fi

If need to match wildcard in the file names

if test -n "$(find /dir/to/search -maxdepth 1 -name 'files*' -print -quit)"
then
    echo found
else
    echo not found
fi

Source:
https://linuxize.com/post/bash-check-if-file-exists/
https://stackoverflow.com/questions/6363441/check-if-a-file-exists-with-wildcard-in-shell-script