constant issue

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

Hello, I'm trying to create a package of contants that I can import into other packages and scripts. In particular, I want to define octal constants for use with the PERL function chmod. Here's my code

package Constants;
use base Exporter; @ISA = qw (Exporter);

@EXPORT = qw( $var1 $var2);
$var1 = \'val1';
$var2 = \'val2';
[download]

This works but I'd wanted to add some octal constants so I added the following code to the above:

use constant  B_OGUS  => 0620;
[download]

I included B_OGUS in @EXPORT which returned in proper value in decimal (400) but not in octal. How can I get the value to return in octal so I can use it in chmod? chmod(B_OGUS,$filename); Thank you

Comment on constant issue Select or Download Code

Replies are listed 'Best First'.
Re: constant issue by ferreira (Chaplain) on Jan 19, 2007 at 16:38 UTC
chmod's first argument is a number, which most of the time is written in source code as an octal number (like `0620`). But this is a convenience for the reader of the code, since octal numbers are much easy to interpret as Unix permission modes (which are split in groups of 3 bits). However, for Perl, this `chmod 400, @files` [download] works the same as `chmod 0620, @files` [download] So I recommend you use your constants just like you did and when you want to take a look at its value use `sprintf "0%o", B_OGUS # returns "0620"` [download] Also be sure to read the note in chmod documentation about this argument as a number and not as a string to avoid another common mistake.	[reply] [d/l] [select]
Re: constant issue by Joost (Canon) on Jan 19, 2007 at 16:38 UTC
You should be able to use decimal 400 as the value, since octal / hexadecimal / decimal literal representations of the same value ARE the same value. 0620 == 400 == 0x190 Note that you can only use octal and hexadecimal notation in numeric literals. ~~String literals~~ Strings used as numbers are always interpreted as decimal (and you should use oct() and hex() to convert octal and hexadecimal strings to numbers. update: note also that numbers converted to string (as in print $number) also always result in decimal notation unless you use special formatting (like printf()) "What should it profit a man, if he should win a flame war, yet lose his cool?"	[reply]
Re: constant issue by ikegami (Patriarch) on Jan 19, 2007 at 16:46 UTC
`400`, `0620` and `400.0`, `4*100` are all the same number. Perl doesn't recognize any difference. They can be used interchangeably. If you use a representation that Perl doesn't recognize, that's when trouble starts. For example, Perl doesn't recognize `'0620'` as a representation of `400`. That means `'0620'` is not the same number as `0620`. (But `oct('0620')` is.)	[reply] [d/l] [select]
Re: constant issue by moklevat (Priest) on Jan 19, 2007 at 16:51 UTC
In addition to the advice provided by the monks above, you may want to consider whether using Readonly might be preferable than using constant in this case. There was a good discussion of this in a thread called Using Constants in Perl.	[reply]