As stated in perlstyle, it is very important that the debugging message includes all of the important information, including the filename. (And for those who think I sound like a broken record on this, spend a couple of hours late at night trying to figure out which file out of several thousand accessed by a script you have never seen broke the production run, and then tell me that insisting on having the filename is unreasonable...)

A few incidental points. The first is that people seeking to slurp a file usually don't want just the first line. And secondly if you make a habit of scoping file handles tightly, there is no need to close them. Your preferences may vary, but I usually don't bother. And finally, as chip says, if you have the choice in 5.6.0+, it is better to use the 3-arg open. See Two-arg open() considered dangerous for details and discussion.

sub slurp_file {
  my $file_name = shift;
  open(my $fh, "<", $file_name) or confess("Cannot read '$file_name': 
+$!");
  wantarray ? <$fh> : join '', <$fh>;
}
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