Sysopen Example Doesn't Work

Question

I got this perl example that's suppose to demonstrate sysopen and printf, except so far it only demonstrates die.

#! /usr/bin/perl  
$filepath = 'myhtml.html';
sysopen (HTML, $filepath, O_RDWR|O_EXCL|O_CREAT, 0755) 
    or die "$filepath cannot be opened.";
printf HTML "<html>\n";

but when I execute the code it just dies.

myhtml.html cannot be opened. at file_handle.pl line 7.

myhtml.html does not exist, but it should have been created by the O_CREAT flag. shouldn't it?

EDIT

I have edited the code to include the suggestions about use strict and $!. Below is the new code and its result.

#! /usr/bin/perl
use strict; 
$filepath = "myhtml.html";

sysopen (HTML, '$filepath', O_RDWR|O_EXCL|O_CREAT, 0755) 
    or die "$filepath cannot be opened. $!";
printf HTML "<html>\n";

output, due to the use strict, gave us a whole bunch of errors:

Global symbol "$filepath" requires explicit package name at file_handle.pl line 3.
Global symbol "$filepath" requires explicit package name at file_handle.pl line 5.
Bareword "O_RDWR" not allowed while "strict subs" in use at file_handle.pl line 5.
Bareword "O_EXCL" not allowed while "strict subs" in use at file_handle.pl line 5.
Bareword "O_CREAT" not allowed while "strict subs" in use at file_handle.pl line 5.
Execution of file_handle.pl aborted due to compilation errors.

EDIT 2

Based on everyone's suggestion and help, here is the final working code:

#! /usr/bin/perl
use strict;
use Fcntl;

my $filepath = "myhtml.html";

sysopen (HTML, $filepath, O_RDWR|O_EXCL|O_CREAT, 0755) 
    or die "$filepath cannot be opened. $!";
printf HTML "<html>\n"; 
....

Accepted Answer

O_RWDR, O_EXCL, and O_CREAT are all constants defined in the Fcntl module. Put the line

use Fcntl;

near the top of your script.

Answer 2

Lots of issues here:

Always put use strict; at the top of your program. That would provide a clue.
The reason the sysopen failed is in the $! variable. You should generally include it in any die message.
As the sysopen entry in man perlfunc explains, the various O_* constants are exported by the Fcntl module. You need to use that module if you want those constants defined. As it is, you're character-wise or-ing together the strings "O_RDWR", "O_EXCL", and "O_CREAT", resulting in another string that sysopen doesn't know what to do with. use strict would prevent this from happening.

Answer 3

myhtml.html file probably already exists. It is probably because a previous execution of the script created it. The O_EXCL flag will cause sysopen to fail if the file exists. Relevant quote from sysopen documentation:

In many systems the O_EXCL flag is available for opening files in exclusive mode. This is not locking: exclusiveness means here that if the file already exists, sysopen() fails.

Sysopen Example Doesn't Work

3 Answers

Must Read

Your Answer

Maya Lin-Takahashi

Sysopen Example Doesn't Work

3 Answers

Must Read

Your Answer

Sign up or log in

Post as a guest

Maya Lin-Takahashi