Perl Or Error Handling
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Syntax Overview Perl - Data Types Perl - Variables Perl - Scalars Perl - Arrays Perl - Hashes Perl - IF...ELSE Perl - Loops Perl - perl error handling best practices Operators Perl - Date & Time Perl - Subroutines Perl - References exception handling in perl try catch Perl - Formats Perl - File I/O Perl - Directories Perl - Error Handling Perl - Special Variables perl error variable Perl - Coding Standard Perl - Regular Expressions Perl - Sending Email Perl Advanced Perl - Socket Programming Perl - Object Oriented Perl - Database Access Perl - CGI Programming
Perl Error Handling Eval
Perl - Packages & Modules Perl - Process Management Perl - Embedded Documentation Perl Useful Resources Perl - Questions and Answers Perl - 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 die function in perl 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 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,
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Perl Die Exit Code
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minute: Sign up perl “or” error handling: multi-statement on error possible? up vote 5 down vote favorite 1 This construct is pretty common in perl: opendir (B,"/somedir") or die "couldn't open dir!"; But this does not seem to work: opendir https://www.tutorialspoint.com/perl/perl_error_handling.htm ( B, "/does-not-exist " ) or { print "sorry, that directory doesn't exist.\n"; print "now I eat fugu.\n"; exit 1; }; Is it possible for the "or" error-handling to have more than one command? Compiling the above: # perl -c test.pl syntax error at test.pl line 5, near "print" syntax error at test.pl line 7, near "}" test.pl had compilation errors. perl share|improve this question asked May 4 '12 at 18:16 raindog308 378412 2 Error prints should be sent to STDERR, http://stackoverflow.com/questions/10454061/perl-or-error-handling-multi-statement-on-error-possible and you should use die instead of print+exit. –ikegami May 4 '12 at 18:24 add a comment| 2 Answers 2 active oldest votes up vote 12 down vote accepted You can always use do: opendir ( B, "/does-not-exist " ) or do { print "sorry, that directory doesn't exist.\n"; print "now I eat fugu.\n"; exit 1; } Or you can use if/unless: unless (opendir ( B, "/does-not-exist " )) { print "sorry, that directory doesn't exist.\n"; print "now I eat fugu.\n"; exit 1; } Or you can swing together your own subroutine: opendir ( B, "/does-not-exist " ) or fugu(); sub fugu { print "sorry, that directory doesn't exist.\n"; print "now I eat fugu.\n"; exit 1; } There is more than one way to do it. share|improve this answer edited May 4 '12 at 21:30 answered May 4 '12 at 18:20 TLP 55k663118 The "more regular" doesn't work, for example, if one uses open(my $B, ...). –ikegami May 4 '12 at 18:25 @ikegami Well, it does work, it just won't be very productive. With global file handle, it shouldn't matter. –TLP May 4 '12 at 18:33 @TLP apart from the scope issue, why do you consider the "unless" solution not recommended? –Bill Ruppert May 4 '12 at 19:27 @bill mostly because of scope. –TLP May 4 '12 at 19:44 add a comment| up vote -2 down vote Exception handling in Perl is done with eval() eval
I: Basic Perl 01-Getting Your Feet Wet 02-Numeric and String Literals 03-Variables 04-Operators 05-Functions 06-Statements 07-Control Statements 08-References Part II: Intermediate Perl 09-Using Files 10-Regular Expressions 11-Creating Reports Part III: Advanced Perl 12-Using Special Variables 13-Handling Errors and Signals 14-What Are Objects? 15-Perl Modules 16-Debugging Perl 17-Command line https://affy.blogspot.com/p5be/ch13.htm Options Part IV: Perl and the Internet 18-Using Internet Protocols ftplib.pl 19-What is CGI? 20-Form Processing 21-Using Perl with Web Servers 22-Internet Resources Appendixes A-Review Questions B-Glossary C-Function List D-The Windows Registry E-What's On the CD? 13 - Handling Errors and Signals Most of the examples in this book have been ignoring the fact that errors can and probably will occur. An error can occur because the directory you are trying to use does error handling not exist, the disk is full, or any of a thousand other reasons. Quite often, you won't be able to do anything to recover from an error, and your program should exit. However, exiting after displaying a user-friendly error message is much preferable than waiting until the operating system or Perl's own error handling takes over. After looking at errors generated by function calls, we'll look at a way to prevent certain normally fatal activities - like perl error handling dividing by zero - from stopping the execution of your script; this is by using the eval() function. Then, you'll see what a signal is and how to use the %SIG associative array to create a signal handling function. Checking for ErrorsThere is only one way to check for errors in any programming language. You need to test the return values of the functions that you call. Most functions return zero or false when something goes wrong. So when using a critical function like open() or sysread(), checking the return value helps to ensure that your program will work properly. Perl has two special variables - $? and $! - that help in finding out what happened after an error has occurred. The $? variable holds the status of the last pipe close, back-quote string, or system() function. The $! variable can be used in either a numeric or a string context. In a numeric context it holds the current value of errno. If used in a string context, it holds the error string associated with errno. The variable, errno, is pre-defined variable that can sometimes be used to determine the last error that took place. Caution You can't rely on these variables to check the status of pipes, back-quoted strings, or the system() function when executing scripts under the Windows operating system. My recommendation is to capture th