Does die have to be used if opening a file fails? - perl

Question

Most of time, I do something like this:
open FH, ">file.txt" or die "Cann't open file: $!";
Does die have to be used? If I want my script to continue (and simply ignore the error if the file cannot be opened), what should I do?

Answer 1

You might want to do something like
if(open my $fh, ">", "file.txt") {
# do stuff with file
close $fh;
}
else {
# do stuff without file
}

Answer 2

The code doesn't have to die if it cannot access the file.
If writing to the file is optional, you might do something like this:
my $file_is_ok = 0;
open FH, ">file.txt" and $file_is_ok = 1;
warn "No logging available" unless $file_is_ok;
Then wherever you want to use the file handle, you can check first that it is ok:
$file_is_ok and print FH "Something happened";
Usually you'll want a little more abstraction than the above, but I hope that is enough to get started.

Answer 3

No, die most definitely doesn't have to be used, or else a failed open would simply exit the program. This is just a commonly used construct since often if you can't open a file there's no point in continuing, but there really is no requirement to die or to do anything else either.

Answer 4

open(my $fh, ">", $file) or print "open failed , you are on your own\n";

Answer 5

I might do something like:
sub process_file {
my $file = shift;
open(my $fh, ">", $file) or return;
# write to file ...
}

Answer 6

It is recommended that you use croak() from Carp instead, especially in modules or objects. See http://perldoc.perl.org/Carp.html
Carp is a standard module and, like all standard modules, comes installed with Perl. A list of all the standard modulesis available in perlmodlib. See http://perldoc.perl.org/perlmodlib.html

Answer 7

Sorry for responding to a few months old question, but the way I do this is by implementing my own die style subroutine:
sub fail {
my $text = $_[0];
# Do error-related stuff here, like send an email
die($text) # or just exit
}
open(my $fh, ">file.txt") or fail("Unable to open file: $!");

Answer 8

You could use a try catch block, using Try::Tiny or something of the sort.

Answer 9

If what you are trying to do is avoid exiting the program when you encounter an error opening a file, omitting the die is not the correct approach. die is Perl's exception mechanism; the fact that it aborts the program by default is an accidental, not fundamental, property. If you supply an exception handler, you retain control. The correct approach is to catch the exception and do your cleanup in the finally block.
use 5.10.0;
use Try::Tiny;
my ($infile, $FH);
try {
open $infile, '<', 'infile.txt' or die "Can't open infile";
try {
open $FH, '>', 'file.txt' or die "Can't open outfile";
my $line = <$infile>;
print $FH $line;
say 'Cleaning up $FH';
close $FH;
} finally {
say 'Cleaning up $infile';
close $infile;
} catch {
die $_;
};
} catch {
die $_;
};
So if open $infile ... fails, die to the catch block, which redies and aborts the script. But once we've opened $infile, if open $FH fails, die to a catch block that also aborts the program but forces close $infile to happen first. File handles aren't the best examples of resources to clean up before program exit because the interpreter closes files automatically, but the basic idea is there.
If you don't like the nested try blocks, you can achieve a very similar effect by checking which exception caused the block to abort and deciding what cleanup is necessary based on that. That's a little more fragile, but still more robust than anything mentioning goto.