See open, -X, and $!.

if (not -e $filename) {
   say "`$filename' does not exist";
   # Your code here. However, see perldoc -f -X
   # for additional test operators you will
   # probably want to use in addition to "exists"
}

# OR

my $fh;
if (not open $fh, '<', $filename) {
    say "Could not open `$filename': $!";
    # Your code here.
}
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