Why not fork of a child process as the target user and directly test if the specific set of files are accessible?

Something like this: (Untested)

#!/usr/bin/perl -w
use strict;
use English;

my $child_pid = open(FROM_KID, "|-")     or die "can't fork: $!";

if ($child_pid)
{
    # am the parent read FROM_KID
    my $child_message = <FROM_KID>;
    
    if( $child_message =~ m/ERROR accessing files/ )
    {
        # Alert the sysadmin
    }
    # Else OK.

    wait $child_pid;    # Wait for the child to quit before continuing
+.
}
else
{
    # Change userID
    $EGID=22;       # aka: $>
    $UID=22;        # aka: $< 
    
    # am the child; use STDIN/STDOUT normally
    if( test_access_files() )
    {
        print "OK accessing files as userID 22\n";
    }
    else
    {
        print "ERROR accessing files as userID 22\n";
    }

    exit;
}
[download]