What's the point of blessed in Perl?

Question

[root@ ~]$ perl -e "print 1 if blessed $a;"
1
[root@ ~]$ perl -e "print 1 if blessed $c;"
1
[root@ ~]$ perl -e "print 1 if blessed $cee;"
1

It seems always true,the version is 5.8.8.

UPDATE

I'm not running as root, it's CHANGED by me for the sake of privacy:)

Running code when you don't know what it does as *root* is probably not the best of ideas! — johnsyweb, Aug 18 '11 at 03:46
possible duplicate of [What exactly does Perl's "bless" do?](http://stackoverflow.com/questions/392135/what-exactly-does-perls-bless-do) — Matt Ball, Aug 18 '11 at 03:50
What is this "`blessed`" you speak of? [The Perl documentation has nothing on it.](http://perldoc.perl.org/search.html?q=blessed) Do you mean "[`bless`](http://perldoc.perl.org/functions/bless.html)"? — jwodder, Aug 18 '11 at 03:55

score 10 · Answer 1 · answered Aug 18 '11 at 04:55

10

blessed is not a keyword in Perl. You are using double quotes in your shell command, so the variables ($a, $c, etc.) are from your shell's environment, they are not Perl variables. Since these environment variables are probably empty, you are essentially executing the script

print 1 if blessed ;

When used like this, blessed is just a bareword string and always evaluates to true. What you have done is not much difference from running

$ perl -e 'print 1 if foo'

answered Aug 18 '11 at 04:55

socket puppet

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Oops, did not occured to me. Because of quotes, I assumed OP is on Windows. Good point. – bvr Aug 18 '11 at 05:03
2

or to make it even clearer, it's like running `perl -e "print 1 if 'blessed'"` – Grant McLean Aug 19 '11 at 00:25

score 8 · Accepted Answer · answered Aug 18 '11 at 04:22

8

Do you mean blessed from Scalar::Util? You probably want to load the function first:

perl -MScalar::Util=blessed -e "print 1 if blessed $a;"

otherwise your blessed is just bareword (string), which is obviously true.

answered Aug 18 '11 at 04:22

bvr

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How can `blessed $a;` be interpreted as bareword? – asker Aug 18 '11 at 04:36
Bareword is not taken as string, as `print test` doesn't output `test`. – asker Aug 18 '11 at 04:52
@asker - `print test` is not good example, as it is parsed to `print test $_` (using test as filehandle). Try `print STDOUT test`. But anyway, in your case `blessed` is not bareword, because of surrounding context (it is interpreted as `$a->blessed` when blessed is not defined) – bvr Aug 18 '11 at 04:56
5

@asker, The shell interpolates an empty string for `$a`, so the code is just `print 1 if blessed `, which is the same as `print 1 if "blessed"` when strict is off. – ikegami Aug 18 '11 at 06:43
@bvr, It is NOT interpreted as `$a->blessed`. That would result in a runtime error. See my message to asker. – ikegami Aug 18 '11 at 06:44
@ikegami - sorry for confusion, on Windows it is and it indeed result in runtime error. – bvr Aug 18 '11 at 09:01
@bvr On my instance of Strawberry Perl (5.12) I get no runtime exception - it prints 1. Perhaps it's time to upgrade :) – Robert P Aug 18 '11 at 17:14
@Robert P, It has nothing to do with the OS, but the shell. @bvr is using `cmd` and I'm guessing you are using `bash`. – ikegami Aug 18 '11 at 18:44
@ikegami nope, I was using cmd on windows. Strawberry Perl is a windows only distribution :) – Robert P Aug 20 '11 at 04:48
@Robert P, No you weren't. Not if you ran the program you said you ran and got the output you said you got. Something you said isn't true. – ikegami Aug 20 '11 at 09:36
@Robert P, Furthermore, I never said you weren't using Windows. If you're on Windows, you're surely using cygwin's `bash`, not `cmd`. Although saying you're on Windows when using cygwin is rather disingenuous, since cygwin is a unix emulation layer. – ikegami Aug 20 '11 at 09:38
@Robert P - I am using quite recent AS perl 5.12.4. When you just run `perl -MO=Deparse -e "print 1 if blessed $a;"` within `cmd` shell, you get `print 1 if $a->blessed;`. Obviously `$a` is not interpolated by the shell. – bvr Aug 20 '11 at 13:33
@bvr: Interesting; now I can reproduce it with Strawberry Perl 5.12.2. Dunno what's going on. :) I think the real answer is: non-strict Perl is insane and should be avoided. – Robert P Aug 20 '11 at 20:05

score 1 · Answer 3 · answered Aug 18 '11 at 04:40

As has been pointed out, you need to load the module before using the method. Also, if you had used perl -we instead of perl -e, you would probably not have asked this question.

For me, with perl -we, I get this warning:

Can't call method "blessed" without a package or object reference at -e line 1.

What's the point of blessed in Perl?

3 Answers3