cgi code line message

[Murcia]

Hi Confreres,
In my cgi I have some break conditions printing a possible error in functions, e.g

open(FILE, "$file") || &error_message("file can not be opened")

. If an errors occurs, I want to know in which line of my code this happens, but to not know how to pass the line number to the error_message subroutine!?

Thanks in advance
Guido

20050606 Janitored by Corion: Removed PRE tag, put HTML formatting instead

[Zaxo]

If you call warn or die without an explicit newline at the end of the message, you'll get file and line number in the text to STDERR.

If you want your own error message function, you can pass it __FILE__ and __LINE__ so that its message gets to refer to the caller's location. Another way to do that is with the caller builtin.

[davido]

Here is a solution that involves a minimal edit to your existing code:

open( FILE, "$file" ) ||
    error_message( "File can not be opened: Line __LINE__.\n" );

But when debugging CGI scripts, CGI::Carp can be much more useful, and would enable you to use die while dumping fatal error messages to the browser.

Update:
Dumb mistake here: __LINE__ doesn't interpolate (nor should it). See my followup: Re^3: cgi code line message. Apologies!

[Murcia]

sorry; but I tried your code and it did not work ... error_message( "File can not be opened: Line ". __LINE__. "\n" ); to be correct ... thanks a lot!

[davido]

My dumb mistake. Forgot that __LINE__ doesn't (and shouldn't) interpolate. Here ya go...

error_message( "File cannot be opened: Line " . __LINE__ . "\n" );

Looks like you already figured it out though. Hope you find it helpful!

[brian_d_foy]

In the error_message() routine, use the caller() function to figure out who called you from where. See the perlfunc entry for examples.

[rupesh]

Just an exerpt from of $! perldoc perlvar.

$! If used numerically, yields the current value of the C "errno"
variable, or in other words, if a system or library call fails,
it sets this variable. This means that the value of $! is
meaningful only *immediately* after a failure:


                if (open(FH, $filename)) {
                    # Here $! is meaningless.
                    ...
                } else {
                    # ONLY here is $! meaningful.
                    ...
                    # Already here $! might be meaningless.
                }
                # Since here we might have either success or failure,
                # here $! is meaningless.

In the above *meaningless* stands for anything: zero, non-zero,
"undef". A successful system or library call does not set the
variable to zero.
If used an a string, yields the corresponding system error
string. You can assign a number to $! to set *errno* if, for
instance, you want "$!" to return the string for error *n*, or
you want to set the exit value for the die() operator.
(Mnemonic: What just went bang?)

[jpeg]

Besides __LINE__, there's the special variable $.
from perldoc perlvar:

$. Current line number for the last filehandle accessed.

Each filehandle in Perl counts the number of lines that have been read from it. (Depending on the value of $/, Perl's idea of what constitutes a line may not match yours.) </quote>

Update: nevermind me, I'm an idiot. $. won't help in this case.
/me wanders off...