Continuously for a file, but alert only once - bash

Question

This post is updated, look below for the solution.
i have the need to check a folder for a presence of a file, which is not always present.
i made a script like this:
#!/bin/sh
while true; do
file=/path/to/file
if [[ "$file" = *filename* ]]
then
echo "$file is present"
else
echo "No present"
fi
sleep 3
done
Works perfectly, except for the fact that the "$file is present" is continuosly repeated, until i delete or move the file.
Which command can I insert after "echo "$file is present" to stop the alert but continue to check for this file (eg when the file will be again available) ?
Thank you.
Since i can't add an answer until 8 hours, i post here my solution:
In anyway i have solved using this script: comparing the time of the file with the current date and then, using "touch" changing the date to 10 seconds ago:
#!/bin/sh
while true
do
cd $(dirname "$0")
current=$(pwd)
cd /boot/home/Downloads
last=$(ls -t | head -n1)
name=$(basename "$last")
filedate=$(date -r "$last" +%G%m%d%H%M%S)
currentdate=$(date +%G%m%d%H%M%S)
if [ "$filedate" -eq "$currentdate" ]
then
echo "$name" "is present"
touch -d '-10 seconds' "$name"
fi
done
Now works as espected and indipendently from the file name!
Alert me about every new file just once and keep to watch that folder :-)
To keep the whole history of script, below there is the script of iamauser. I have a little bit improved this script: now it alert me for every new file (indipendentely from name, kind and so on) inside a folder and also alert me for deleted files :-)
#!/bin/bash
cd /boot/home
filename=$(ls -t | head -n1)
tstamp=$(stat --print "%Y" "$filename")
while true; do
prev=$(ls "/boot/home/Downloads" | tr '\n' '\n' > /tmp/prev.txt)
check=$(ls -t /boot/home/Downloads | head -n1)
if [ ! -d "$filename" ]; then
after=$(ls "/boot/home/Downloads" | tr '\n' '\n' > /tmp/after.txt)
echo "Not present";
sleep 5;
elif [[ "$filename" == "$filename" && $tstamp -ne $(stat --print "%Y" "$filename") ]]; then
sleep 2
difference=$(comm -2 -3 "/tmp/after.txt" "/tmp/prev.txt">/tmp/Diff.txt)
lost=$(cat /boot/common/cache/tmp/Diff.txt)
alert --idea "/boot/home/Downloads: $check is the most recent file in this folder.";
alert --idea "/boot/home/Downloads: $lost removed.";
tstamp=$(stat --print "%Y" "$filename")
else
sleep 3;
fi
done

Answer 1

Something like this may work. I am checking the timstamp of the file to check if there is a new copy of the same filename in the folder.
#!/bin/bash
filename="/path/to/file"
tstamp=$(stat --print "%Y" "$file")
while true; do
if [ ! -f "$filename" ]; then
echo "Not present";
sleep 5;
elif [[ "$filename" == "myfile" && $tstamp -ne $(stat --print "%Y" "$filename") ]]; then
echo "$filename is present";
tstamp=$(stat --print "%Y" "$filename")
else
sleep 3;
fi
done
I tested the script, by touching the filename while the script was running, each time I touched, it printed $filename is present.

Answer 2

Sure, konsolebox; you're right. my script isn't perfect also if i add a sleep to reduce CPU usage.
In anyway, maybe, i miss something with the script from iamauser:
The above script print the echo out when the file is not present, but doesn't print echo out when is present.. Why?
In anyway, since i'd like to experiment, i was also thinking to another way: check the number of files inside a folder using "ls -1 | wc -l", a new file is added and the number of files is +1 than "ls -1 | wc -l"
and, so, i can be alerted indipendently from the file name.. If there is any kind of file with any name, the script should alert me once, while keep to check for new files in the folder.
Any other suggestion?
Thank you!
UPDATE
Ok: this is the definitive revision of the script:
When a new file is written in a folder, this script alert me about. And if I remove this file, the script will alert me, of the most recent file present in that folder.
Very nice, since this is what i was looking for :-)
Since I am on Haiku, i have also replaced the "echo" with alert, an alert window, a sort of graphic "echo".
#!/bin/bash
cd /boot/home
filename=$(ls -t | head -n1)
tstamp=$(stat --print "%Y" "$filename")
while true; do
check=$(ls -t /boot/home/Downloads | head -n1)
if [ ! -d "$filename" ]; then
echo "Not present";
sleep 5;
elif [[ "$filename" == "$filename" && $tstamp -ne $(stat --print "%Y" "$filename") ]]; then
alert --idea "/boot/home/Downloads: $check is the most recent file in this folder";
tstamp=$(stat --print "%Y" "$filename")
else
sleep 3;
fi
done