test if statement from database

[ef]

Hi,

I have an compare statement stored in the database. e.g. 'fieldx > 10'.
I read that and want to use that directly in a perl statement, something
like

$iffromdatabase =~ s/fieldx/realvalueoffieldx/;
if ( /$iffromdatabase/e ){
.....
}

can this be done somehow?

Bo.

 

[Gunnar Hjalmarsson]

I have an compare statement stored in the database. e.g. 'fieldx > 10'.
I read that and want

Did you read *why* you want it?

to use that directly in a perl statement, something like

$iffromdatabase =~ s/fieldx/realvalueoffieldx/;
if ( /$iffromdatabase/e ){
.....
}

can this be done somehow?

Yes. Check e.g.

perldoc -q "expand variables"
perldoc -f eval

 

[xhoster]

Hi,

I have an compare statement stored in the database. e.g. 'fieldx > 10'.
I read that and want to use that directly in a perl statement, something
like

$iffromdatabase =~ s/fieldx/realvalueoffieldx/;
if ( /$iffromdatabase/e ){
.....
}

can this be done somehow?

You could probably do this with eval, but you would probably be better
off doing something like:

my ($field,$op,$constant) = $fromdb =~ /$(.*) (>) (.*)$/ or die;

if (apply_logic($valueof{$field},$op,$constant)) {
#...
};

sub apply_logic {
return $_[0] < $_[2] if $_[1] eq '<';
return $_[0] > $_[2] if $_[1] eq '>';
return $_[0] == $_[2] if $_[1] eq '==';
die "Don't know how to $_[1]"
};

Xho

 

[A. Sinan Unur]

....
You could probably do this with eval, but you would probably be better
off doing something like:

my ($field,$op,$constant) = $fromdb =~ /$(.*) (>) (.*)$/ or die;

Based on apply_logic below, this should probably be (untested):

sub apply_logic {
return $_[0] < $_[2] if $_[1] eq '<';
return $_[0] > $_[2] if $_[1] eq '>';
return $_[0] == $_[2] if $_[1] eq '==';
die "Don't know how to $_[1]"
};

Nice, very nice.

Sinan

 

[xhoster]

Based on apply_logic below, this should probably be (untested):

my ($field,$op,$constant) = $fromdb =~ /$(.*) (<|=|>) (.*)$/ or die;

Yes, and also the first $ in the regex should be ^.
(But still untested).


Come to think of it, just
my ($field,$op,$constant)= split ' ', $fromdb;
might be better, as then the operator only needs be validated in
apply_logic rather than in two places. Provided of course that
white space is appropriate as a delimiter.


Xho

 

[ef]

Thanks for the suggestions, i will test it.

Bo.

Yes, and also the first $ in the regex should be ^.
(But still untested).


Come to think of it, just
my ($field,$op,$constant)= split ' ', $fromdb;
might be better, as then the operator only needs be validated in
apply_logic rather than in two places. Provided of course that
white space is appropriate as a delimiter.


Xho