Assigning Null to a variable

Ombongi.Moraa has asked for the wisdom of the Perl Monks concerning the following question:

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Re: Assigning Null to a variable by Corion (Patriarch) on Jul 02, 2012 at 13:16 UTC
You don't assign a space to a string by assigning it the empty string. Compare the two following statements: `#1234567890123 my $foo = ''; # Empty string my $bar = ' '; # String with a space` [download] Neither of them is the "null" value in Perl. The thing that comes closest to a "null" value is undef.	[reply] [d/l]
Re: Assigning Null to a variable by Eliya (Vicar) on Jul 02, 2012 at 13:31 UTC
`for (1..$length) { my $alphanumber .= $chars[int rand @chars]; } ^^` [download] Most likely, your real problem is the above `my` ...	[reply] [d/l] [select]
Re: Assigning Null to a variable by frozenwithjoy (Priest) on Jul 02, 2012 at 14:31 UTC
This isn't related to what you are asking about, but for future questions, it makes it a lot easier to read if you put tags around your code and add other appropriate formatting. Check out Markup in the Monastery. Also, if you look at the code you posted, the square brackets vanished and turned the text inside to a link because outside of code tags, square brackets are used for creating links (checkout What shortcuts can I use for linking to other information? for more info.)	[reply]
Re: Assigning Null to a variable by Anonymous Monk on Jul 03, 2012 at 02:23 UTC
What is the correct definition of False and Null in Perl? Validation: is defined whether the variable? True or False? A Quick Reference Guide What is truth? (Curiosity corner) When does while() test for defined vs truth	[reply]
Re: Assigning Null to a variable by Anonymous Monk on Jul 02, 2012 at 15:02 UTC
Perl does not have a value to correspond to the SQL notion of `NULL`. It only has `undef`. It does not have a built-in concept of "I know what the value is, and the value is: that it is known that it has no value at all."	[reply]
Re^2: Assigning Null to a variable by AnomalousMonk (Archbishop) on Jul 02, 2012 at 15:34 UTC
I don't know enough about SQL to know how its `NULL` compares to Perl's undef, but it strikes me that "I know what the value is, and the value is: that it is known that it has no value at all" is actually a pretty good (Update: well, on second thought, perhaps just a bit wordy) explanation of our friend `undef`!	[reply] [d/l] [select]
Re^3: Assigning Null to a variable by afoken (Chancellor) on Jul 02, 2012 at 19:13 UTC
"I know what the value is, and the value is: that it is known that it has no value at all" is actually a pretty good explanation of our friend `undef`! ... and that's why DBI maps SQL's `NULL` to `undef` and vice versa. Alexander -- Today I will gladly share my knowledge and experience, for there are no sweeter words than "I told you so". ;-)	[reply] [d/l] [select]
Re^2: Assigning Null to a variable by cavac (Prior) on Jul 02, 2012 at 15:10 UTC
You could still use it that way in arrays. For hashes there is "exists" vs. "defined", see `perldoc -f exists`. If haven't tested it now (working from memory and POD), but this looks like it fits the bill. Sorry for any bad spelling, broken formatting and missing code examples. During a slight disagreement with my bicycle (which i lost), i broke my left forearm near the elbow. I'm doing the best i can here...	[reply] [d/l]