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Lyvois
#1 / 9
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 Using Eval Statement To Trap Module Not Present Fatal Error Can someone please tell me what's wrong below. I am trying to trap a fatal
error if a module is not installed when calling that module via a use
statement but doing the eval statement first is not catching the error is
the File::Find module is not present.
# get our total disk space
# we are using the File::Find module but just in case
# it is not available on a server, we want to trap
# a fatal error first.
$result = eval("use File::Find");
my $disk_space = "Unable To Determine";
} else { # we can use it so let's get our disk space
find(\&stat, "$cgi_path");
find(\&stat, "$public_path");
my $megabytes = $filesize / 1000000;
$disk_space = sprintf("%.02f",$megabytes);
$disk_space .= " MB";
}
sub stat
{
$filesize += (stat("$_"))[7];
Quote: }
Thank you.
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| Sun, 25 Sep 2005 17:25:50 GMT |
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Tassilo v. Parseva
#2 / 9
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Using Eval Statement To Trap Module Not Present Fatal Error Also sprach Lyvoise:
Quote: > Can someone please tell me what's wrong below. I am trying to trap a fatal
> error if a module is not installed when calling that module via a use
> statement but doing the eval statement first is not catching the error is
> the File::Find module is not present.
Actually I doubt that. Your code below should catch these cases.
However, there are some things you should change in the code:
Quote: > # get our total disk space > # we are using the File::Find module but just in case
> # it is not available on a server, we want to trap
> # a fatal error first.
> $result = eval("use File::Find");
and not needed in this case. Block eval (along with require() instead of
use()) would be the way to go.
In the case of File::Find you should do that in a BEGIN block because
some of the functions have a prototype that would otherwise be lost. So
I'd suggest doing it that way:
my $HAVE_FILE_FIND;
BEGIN {
eval { require File::Find };
File::Find->import;
$HAVE_FILE_FIND = 1;
}
}
Calling File::Find->import is necessary if you want this module to
export its default symbols such as find() and finddepth().
if (! $HAVE_FILE_FIND) {
Quote: > my $disk_space = "Unable To Determine";
Declaring and using the lexical in this if-branch is probably not what
you want. $disk_space will disappear once you leave this block. You must
probably declare $disk_space before entering the if-else blocks.
Quote: > } else { # we can use it so let's get our disk space > find(\&stat, "$cgi_path"); > find(\&stat, "$public_path"); > my $megabytes = $filesize / 1000000;
> $disk_space = sprintf("%.02f",$megabytes);
> $disk_space .= " MB";
> }
> sub stat
> {
> $filesize += (stat("$_"))[7];
> }
Tassilo
--
{
pam{rekcahbus})(rekcah{lrePbus})(lreP{rehtonabus})!JAPH!qq(rehtona{tsuJbus#;
$_=reverse,s+(?<=sub).+q#q!'"qq.\t$&."'!#+sexisexiixesixeseg;y~\n~~dddd;eval
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| Sun, 25 Sep 2005 18:09:24 GMT |
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Gunnar Hjalmarsso
#3 / 9
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Using Eval Statement To Trap Module Not Present Fatal Error Quote:
> Can someone please tell me what's wrong below. I am trying to trap > a fatal error if a module is not installed when calling that module > via a use statement but doing the eval statement first is not > catching the error is the File::Find module is not present. > <snip>
> $result = eval("use File::Find");
The use pragma looks for a module at compile-time. Try this instead:
eval { require File::Find };
/ Gunnar
--
Gunnar Hjalmarsson
Email: http://www.gunnar.cc/cgi-bin/contact.pl
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| Sun, 25 Sep 2005 18:07:28 GMT |
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Tassilo v. Parseva
#4 / 9
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Using Eval Statement To Trap Module Not Present Fatal Error Also sprach Gunnar Hjalmarsson:
Quote:
>> Can someone please tell me what's wrong below. I am trying to trap >> a fatal error if a module is not installed when calling that module >> via a use statement but doing the eval statement first is not >> catching the error is the File::Find module is not present. >> <snip>
>> $result = eval("use File::Find");
> The use pragma looks for a module at compile-time. Try this instead:
> eval { require File::Find };
Not when wrapped in string-eval. It might well be the only situation
where use() does not happen at compile time.
Tassilo
--
{
pam{rekcahbus})(rekcah{lrePbus})(lreP{rehtonabus})!JAPH!qq(rehtona{tsuJbus#;
$_=reverse,s+(?<=sub).+q#q!'"qq.\t$&."'!#+sexisexiixesixeseg;y~\n~~dddd;eval
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| Sun, 25 Sep 2005 19:37:57 GMT |
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Gunnar Hjalmarsso
#5 / 9
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Using Eval Statement To Trap Module Not Present Fatal Error Quote:
> Also sprach Gunnar Hjalmarsson:
>>> $result = eval("use File::Find");
>> The use pragma looks for a module at compile-time. Try this
>> instead:
>> eval { require File::Find };
> Not when wrapped in string-eval.
Didn't know that; thanks for correcting me!
Quote: > It might well be the only situation where use() does not happen at
> compile time.
My usual luck. :(
/ Gunnar
--
Gunnar Hjalmarsson
Email: http://www.gunnar.cc/cgi-bin/contact.pl
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| Sun, 25 Sep 2005 21:24:48 GMT |
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Benjamin Goldber
#6 / 9
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Using Eval Statement To Trap Module Not Present Fatal Error
[snip]
Quote: > First of all, you are using string-eval here. It works but it is slower > and not needed in this case. Block eval (along with require() instead > of use()) would be the way to go. > In the case of File::Find you should do that in a BEGIN block because
> some of the functions have a prototype that would otherwise be lost. So
> I'd suggest doing it that way:
> my $HAVE_FILE_FIND;
> BEGIN {
> eval { require File::Find };
> File::Find->import;
> $HAVE_FILE_FIND = 1;
> }
> }
use constant HAVE_FILE_FIND => eval {
require File::Find;
File::Find->import;
1;
} || 0;
That way, a block of code like:
if( HAVE_FILE_FIND ) {
....
}
Gets optomized away, if File::Find wasn't found.
--
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| Sun, 25 Sep 2005 22:11:40 GMT |
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Tassilo v. Parseva
#7 / 9
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Using Eval Statement To Trap Module Not Present Fatal Error Also sprach Benjamin Goldberg:
Quote:
>> my $HAVE_FILE_FIND; >> BEGIN { >> eval { require File::Find };
>> File::Find->import; >> $HAVE_FILE_FIND = 1; >> } >> } > I would write that as:
> use constant HAVE_FILE_FIND => eval {
> require File::Find;
> File::Find->import;
> 1;
> } || 0;
> That way, a block of code like:
> if( HAVE_FILE_FIND ) {
> ....
> }
> Gets optomized away, if File::Find wasn't found.
And it looks even less cluttered. Nice!
Tassilo
--
{
pam{rekcahbus})(rekcah{lrePbus})(lreP{rehtonabus})!JAPH!qq(rehtona{tsuJbus#;
$_=reverse,s+(?<=sub).+q#q!'"qq.\t$&."'!#+sexisexiixesixeseg;y~\n~~dddd;eval
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| Mon, 26 Sep 2005 06:13:59 GMT |
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Anno Sieg
#8 / 9
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Using Eval Statement To Trap Module Not Present Fatal Error
Quote:
> > Also sprach Gunnar Hjalmarsson:
> >>> $result = eval("use File::Find");
> >> The use pragma looks for a module at compile-time. Try this
> >> instead:
> >> eval { require File::Find };
> > Not when wrapped in string-eval.
> Didn't know that; thanks for correcting me!
> > It might well be the only situation where use() does not happen at
> > compile time.
> My usual luck. :(
Strictly speaking, it *does* happen at compile time -- the time the
string inside eval() is compiled. Since that compilation happens
at run-time of the file, the effect is the same.
Anno
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| Mon, 26 Sep 2005 10:08:56 GMT |
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Lyvois
#9 / 9
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Using Eval Statement To Trap Module Not Present Fatal Error Thanks everyone for the help. It correctly trapping all errors now. Very
much appreciated.
Lyvoise
Quote: > Can someone please tell me what's wrong below. I am trying to trap a fatal > error if a module is not installed when calling that module via a use > statement but doing the eval statement first is not catching the error is > the File::Find module is not present. > # get our total disk space
> # we are using the File::Find module but just in case
> # it is not available on a server, we want to trap
> # a fatal error first.
> $result = eval("use File::Find");
> my $disk_space = "Unable To Determine";
> } else { # we can use it so let's get our disk space
> find(\&stat, "$cgi_path");
> find(\&stat, "$public_path");
> my $megabytes = $filesize / 1000000;
> $disk_space = sprintf("%.02f",$megabytes);
> $disk_space .= " MB";
> }
> sub stat
> {
> $filesize += (stat("$_"))[7];
> }
> Thank you.
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| Mon, 26 Sep 2005 21:41:23 GMT |
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