Re^3: not able to make defined-or operator work in my code

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Re^4: not able to make defined-or operator work in my code by davido (Cardinal) on Feb 11, 2015 at 02:05 UTC
Set an environment variable, "`PERL_MTYEST=''`", and then run the following script: `use feature qw/say/; say exists($ENV{PERL_MYTEST}) ? "exists" : "doesn't exist"; say defined($ENV{PERL_MYTEST}) ? "defined" : "undefined"; say length($ENV{PERL_MYTEST}) ? "non-zero length" : "zero length"; say "<<$ENV{PERL_MYTEST}>>";` [download] The output will be: `exists defined zero length <<>>` [download] Which indicates that setting an environment variable to '' (an empty string) does not create an undefined variable, but rather, a defined variable with a value of zero length. Your assumption is just incorrect, that's all. Test for length. If you unset the environment variable in question, and then run the same test, you will get "doesn't exist", and "undefined". I suppose it's possible that your mileage will vary depending on operating system, but I don't know what OS would do it differently. Dave	[reply] [d/l] [select]
Re^4: not able to make defined-or operator work in my code by dsheroh (Monsignor) on Feb 11, 2015 at 08:20 UTC
I did define a value. Yes, you did. You defined a value. That is why the value is not undefined. The value you defined happens to be an empty string, but an empty string is still a defined value.	[reply]
Re^5: not able to make defined-or operator work in my code by lonewolf28 (Beadle) on Feb 12, 2015 at 00:22 UTC
Dave, I'd appreciate you for enlightening me. Thanks. :-)	[reply]