Perl Error Handling Best Practices
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Exception Handling In Perl Try Catch
vote 13 down vote favorite 8 I'm learning Perl, and in a lot of the examples I see errors are handled like this open FILE, "file.txt" or die $!; Is die in the middle of a script really the best way to deal with an error? perl error-handling share|improve this question edited May 19 '10 at 20:55 brian d foy 87.1k24150391 asked May 19 '10 at 20:49 Mike 15.6k50138177 perl error handling eval 6 For discussions of perl exceptions, see What's broken about exceptions in perl?, Do you use an exception class in your Perl programs? Why or why not?, and Object-oriented exception handling in Perl -- is it worth it? –Ether May 19 '10 at 22:14 add a comment| 5 Answers 5 active oldest votes up vote 20 down vote accepted Whether die is appropriate in the middle of the script really depends on what you're doing. If it's only tens of lines, then it's fine. A small tool with a couple hundred lines, then consider confess (see below). If it's a large object-oriented system with lots of classes and interconnected code, then maybe an exception object would be better. confess in the Carp package: Often the bug that led to the die isn't on the line that die reports. Replacing die with confess (see Carp package) will give the stack trace (how we got to this line) which greatly aids in debugging. For handling exceptions from Perl builtins, I like to use autodie. It catches failures from open and other system calls and will throw exceptions for you, without having to do the or die bit. These exceptions can be caught with a eval
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few tips, we'll be covering current best practices for programming Perl. In this tip we talk about smart exception handling. Exception handling All http://perltraining.com.au/tips/2011-02-09.html of Perl's built-in functions are silent on failure. This means that we have http://programmers.stackexchange.com/questions/147059/the-modern-way-to-perform-error-handling to write a lot of code like this: open my $fh, "<", $filename or die "Failed to open $filename $!"; while(<$fh>) { } close $fh or die "Failed to close filehandle: $!"; This is problematic, because if we forget to check for an error, then we may never know that perl error there was a problem. Fortunately, from 5.10.1 autodie comes standard with Perl so now we can allow autodie to do our error handling for us. autodie changes all of Perl's built-in functions to throw an exception on failure. use autodie; open my $fh, "<", $filename; while(<$fh>) { } close $fh; Handling exceptions with Try::Tiny The old way of throwing exceptions was to use perl error handling block eval. This looks ugly, isn't consistent with other languages, and is easily confused with string eval. eval { die "Exception thrown"; }; if( $@ ) { warn "caught error: $@"; } Other languages use try and catch blocks for the same thing. try to run this code, and catch any errors it might generate. With Try::Tiny we can have the same semantics: use Try::Tiny; try { die "Exception thrown"; } catch { warn "caught error: $_"; }; There's also a finally block which will be run, whether or not any exceptions were thrown and caught. Throwing exceptions from the perspective of the caller In your code, and especially in your modules, you should also throw exceptions on failure. This means that errors will not be silently ignored while the program does the wrong thing. If, however, you are throwing an exception from a module, you probably don't want the error message to point to the line in your module that threw the error, but rather the line from which your subroutine was erroneously called. For example this package allows us to generate greetings in different languages: p
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