Custom Backend not recognized

I am trying to create a custom backend.
I followed instructions to create a backend "for debbuging" : a "tofile" backend.

I registered it in /usr/lib/cups/backend and restarted the service.
But when I try :

lpinfo -v


It doesn't show, and in my error_logs I Have :

[cups-deviced] PID 8330 (tofile) stopped with status 8!


Here aree the permission :

-rwxr-xr-x 1 root root 715 juil. 1 10:38 tofile


I found a topic about the problem, I have not this error for the same reason (No trailing whitespace in script, ...).
When I use :

sudo file /usr/lib/cups/backend/tofile
/usr/lib/cups/backend/tofile: ASCII text


I also heard about the cupsd.conf using file-device, but it is marked as deprecated in the documentation...

Obviously, the script is the same as in the tutorial :

#! /bin/bash
# Have debug info in /var/log/cups/error_log:
set -x
# Output "device discovery" information on stdout:
if test "$#" = "0"
then echo 'direct tofile:/tmp/tofile.out "Unknown" "/tmp/tofile.out"'
exit 0
fi
# Have the input at fd0 (stdin) in any case:
test -n "$6" && exec <"$6"
# Infinite retries to access the file:
until cat /dev/null >/tmp/tofile.out
do echo 'INFO: cannot access /tmp/tofile.out - retry in 30 seconds' 1>&2
sleep 30
done
echo 'INFO: sending data to /tmp/tofile.out' 1>&2
# Forward the data from stdin to the file:
if cat - >/tmp/tofile.out
then echo 'INFO:' 1>&2
exit 0
else echo 'ERROR: failed to send data to /tmp/tofile.out' 1>&2
exit 1
fi


(but without the trailing space at the first line ^^ !)

#!/bin/bash

set -x

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