check receiving of a new file via filedate

bash_filedate_checker.sh

#!/bin/bash
set -e

filename="./my-file"
waitseconds=30

now=$(date +%s)
timeout=$(( now + waitseconds ))
file_modified=$(stat -c '%Y' $filename)

echo "wait for $filename ... time: $wait"

# check if file $filename is older than 30 seconds
# we assume, that when it is older than 30 seconds, we have an old file, we wait for a new one
while [[ $(( ($(date +%s) - $file_modified) > (waitseconds) )) == 1 ]]
do
        # if now is > timeout, exit, else we wait a little bit
        if [[ (( $(date +%s) -ge $timeout )) ]]; then exit 1; fi;
        sleep 5
        file_modified=$(stat -c '%Y' $filename)
done

echo "found new file"