Error Handling In Perl
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Quick Guide Perl - Functions References Perl - Useful Resources Perl - Discussion Selected Reading Developer's Best Practices Questions and Answers Effective Resume Writing HR Interview Questions Computer Glossary Who is Who Perl - Error Handling Advertisements Previous Page Next Page The execution and the errors always go together. If you are opening a file which does not exist. then if you did not handle this situation properly then your program inheritance and error handling in perl is considered to be of bad quality. The program stops if an error occurs. So a proper error handling is used to handle various type of errors, which may occur during a program execution and take appropriate action instead of halting program completely. You can identify and trap an error in a number of different ways. Its very easy to trap errors in Perl and then handling them properly. Here are few methods which can be used. The if statement The if statement is the obvious choice when you need to check the return value from a statement; for example − if(open(DATA, $file)){ ... }else{ die "Error: Couldn't open the file - $!"; } Here variable $! returns the actual error message. Alternatively, we can reduce the statement to one line in situations where it makes sense to do so; for example − open(DATA, $file) || die "Error: Couldn't open the file $!"; The unless Function The unless function is the logical opposite to if: statements can completely bypass the success status and only be executed if the expression returns false. For example − unless(chdir("/etc")){ die "Error: Can't change directory - $!"; } The unless statement is best used when you want to raise an error or alternative only if the expression fail
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A • B • C • D • E F • G • H • I • L M • N • O • P • S T • U • X eval Perl 5 version 24.0 documentation Go to top Show recent pages Home > http://perldoc.perl.org/functions/eval.html Language reference > Functions > eval Please note: Many features of this site require JavaScript. You appear to have JavaScript disabled, or are running a non-JavaScript capable web browser. To get the best experience, please enable JavaScript http://www.perlmonks.org/?node_id=1102209 or download a modern web browser such as Internet Explorer 8, Firefox, Safari, or Google Chrome. Recently read eval Perl functions A-Z | Perl functions by category | The 'perlfunc' manpage eval EXPR eval BLOCK eval error handling In the first form, often referred to as a "string eval", the return value of EXPR is parsed and executed as if it were a little Perl program. The value of the expression (which is itself determined within scalar context) is first parsed, and if there were no errors, executed as a block within the lexical context of the current Perl program. This means, that in particular, any outer lexical variables are visible to error handling in it, and any package variable settings or subroutine and format definitions remain afterwards. Note that the value is parsed every time the eval executes. If EXPR is omitted, evaluates $_ . This form is typically used to delay parsing and subsequent execution of the text of EXPR until run time. If the unicode_eval feature is enabled (which is the default under a use 5.16 or higher declaration), EXPR or $_ is treated as a string of characters, so use utf8 declarations have no effect, and source filters are forbidden. In the absence of the unicode_eval feature, will sometimes be treated as characters and sometimes as bytes, depending on the internal encoding, and source filters activated within the eval exhibit the erratic, but historical, behaviour of affecting some outer file scope that is still compiling. See also the evalbytes operator, which always treats its input as a byte stream and works properly with source filters, and the feature pragma. Problems can arise if the string expands a scalar containing a floating point number. That scalar can expand to letters, such as "NaN" or "Infinity" ; or, within the scope of a use locale , the decimal point character may be something other than a dot (such as a comma). None of these are likely to pa
Tutorials Poetry RecentThreads NewestNodes Donate What'sNew on Sep 27, 2014 at 11:31UTC ( #1102209=perlquestion: print w/replies, xml ) Need Help?? v_melnik has asked for the wisdom of the Perl Monks concerning the following question: Dear colleagues, I think, it's a matter of religion, but I'd like to get to know more on how other people, more experienced, prefer to handle errors/exceptions in respect to the structure of your programs. Let me describe how I'm doing it now and, if you have some time to share your experience, I'd be very grateful to you for describing how do you prefer to do it. My own "rules" for myself are quite simple. Don't die() while executing a subrotine or method. Only the main module can die() if something goes wrong. Nobody can predict where the class will be used, so an unexpected die() can break the caller's logic. If I've got an exception inside of a subroutine, the subroutine may return(undef). If everything's fine, it return's some value (it can be true or false - no matter), but if some error has been occuried (e.g. if we can't get data from the database), the undef shall be returned. That's okay, but how to let the caller know what's happened with the subroutine? As I think, the caller must have some explaination to be able to write something to the log-file or to show the error message to the operator. So, there is one more rule. Any class may have the "errstr" attribute, so if its' methor returned undef, the caller may get the explaination from this attribute. So, usually it looks like this: package SomeClass; #... sub some_method { # ... eval { die("Oops!"); }; if($@) { $self->{'errstr'} = "Something has gone wrong: $@"; return(undef) } # ... } #... package main; #... my $result = $obj->some_method; unless(defined($result)) { die("Can't SomeClass->some_method(): $obj->{'errstr'}"); } #... [download] And, when something goes wrong, I can get something like that: Can't SomeClass->some_method(): Can't AnotherClass->another_method(): Can't OtherClass->other_method(): Can't open(): No such file at script