Define constant in loop

penantes has asked for the wisdom of the Perl Monks concerning the following question:

Hi there,
the following code is giving me an error:

$Threscount=0;
open(THRESHOLDS, "$Thresholds") or die("Could not open Thresholds file
+.");
foreach (<THRESHOLDS>) {
 chomp($_);
 if ($_ =~/^(\w+);(\d+);$/ && $_ !~/^\#/) {
  print "DEBUG: use constant $1 => $2;\n";
  use constant $1 => $2;
  log_msg("Setting: use constant $1 => $2;");
  if ($Threslabels[$Threscount] ne $1) {
   log_msg("There is something wrong with the thresholds labels, check
+ thresholds file!");
   exit(2);
  }
 $Threscount++;
 }
}
if ($Threscount != 8) {
print "$Threscount\n";
 log_msg("Wrong number of thresholds they should be 8 there are $Thres
+count");
 exit(2);
}
close(THRESHOLDS);
[download]

Constant name '' is invalid at ./getlogs.pl line 75
BEGIN failed--compilation aborted at ./getlogs.pl line 75.
Thanks monks.
Nuno A

Further Details
Im trying to read the thresholds from a file since im going to compile de the script with pp it would be easier to have a wana be conf file.
Trying to substitute this dynamically:

#Define Warning values
use constant  SIMULWAR => 30;
use constant MEMINUSEWAR => 200000000;
use constant SIMULSNAGWWAR => 40;
use constant CONDBWAR => 200;

#Define Critical Values
use constant SIMULCRIT => 50;
use constant MEMINUSECRIT => 240000000;
use constant SIMULSNAGWCRIT => 60;
use constant CONDBCRIT => 240;
[download]

Comment on Define constant in loop Select or Download Code

Replies are listed 'Best First'.
Re: Define constant in loop by artist (Parson) on Feb 23, 2005 at 16:23 UTC
Constant are set at compile time, rather than run time. There is no value for $1 in 'use constant $1=> $2' yet.	[reply]
Re^2: Define constant in loop by penantes (Acolyte) on Feb 23, 2005 at 16:34 UTC
Hmm I see, thank you for your answer. Best Regards, Nuno A	[reply]
Re: Define constant in loop by dragonchild (Archbishop) on Feb 23, 2005 at 18:04 UTC
(Try answering the question vs. saying it can't be done! Grrr.) As use is a compile-time statement, you will need to use eval to do this at run-time. `foreach (<THRESHOLDS>) { chomp($_); if (my ($name, $value) = $_ =~/^(\w+);(\d+);$/ && $_ !~/^\#/) { eval "use constant $name => $value;"; log_msg("Setting: use constant $name => $value;"); if ($Threslabels[$Threscount] ne $name) { log_msg("There is something wrong with the thresholds labels, check + threshold +s file!"); exit(2); } $Threscount++; } }` [download] Also, note that I changed your use of $1 and $2 by assigning them to normal variables. This is a safety as well as documentation thing. Being right, does not endow the right to be rude; politeness costs nothing. Being unknowing, is not the same as being stupid. Expressing a contrary opinion, whether to the individual or the group, is more often a sign of deeper thought than of cantankerous belligerence. Do not mistake your goals as the only goals; your opinion as the only opinion; your confidence as correctness. Saying you know better is not the same as explaining you know better.	[reply] [d/l]
Re: Define constant in loop by TedYoung (Deacon) on Feb 23, 2005 at 16:34 UTC
Also note that constant won't let you declare constants like $1. These kinds of variables have special properties and declaring them constant would be a bad thing, if even possible. And constants are not used like normal variables: `# You don't declare a constant like this: use constant $FOO => 1; # bad # You do it this way use constant FOO => 1; # And use it like this: print FOO;` [download] Ted Young `($$<<$$=>$$<=>$$<=$$>>$$) always returns 1. :-)`	[reply] [d/l] [select]
Re: Define constant in loop by Tanktalus (Canon) on Feb 23, 2005 at 17:58 UTC
Now that everyone has told you why it doesn't work, here's one solution to getting it to work: `if ($_ =~/^(\w+);(\d+);$/ && $_ !~/^\#/) { print "DEBUG: use constant $1 => $2;\n"; eval "use constant $1 => $2"; #...` [download] The idea is to use $1 as a bareword, and $2 similarly. Note that this doesn't work so hot if $2 could be a string (which it isn't in your case). Unfortunately, it makes all your constants not easily accessable: you'll need to call them like `MEMINUSEWAR()` (with the parens) or similar. Barewords won't work. Another alternative is something like this: `use strict; require constant; while (<DATA>) { if (/^(\w+);(\d+);$/) { #eval "use constant $1 => $2"; constant->import({$1 => $2}); } } print MEMINUSEWAR(); __DATA__ MEMINUSEWAR;2000000;` [download] Don't do that either. The best idea is to take all these values and put them in a hash - even a global hash. And access them through that.	[reply] [d/l] [select]