Default VAriable

[R Huber]

Greeting:

When I execute the following:

<>;
print;

I get the error message "Use of uninitialized value in
print"

but when I exectue:

while (<>) {
print;
}

I get what I type in echoed back to my screen.

Why does the first snippet of code get an error
message and the second not?
Thanks,
rj

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[John McKown]

On Tue, 3 Feb 2004, r huber wrote:

> Greeting:
>
> When I execute the following:
>
> <>;
> print;
>
> I get the error message "Use of uninitialized value in
> print"
>
> but when I exectue:
>
> while (<>) {
> print;
> }
>
> I get what I type in echoed back to my screen.
>
> Why does the first snippet of code get an error
> message and the second not?
> Thanks,
> rj

This behaviour is normal and is documented on the Web at:

[url]http://www.perldoc.com/perl5.8.0/pod/perlop.html#I-O-Operators[/url]

It says (quoting)
<quote>

Ordinarily you must assign the returned value to a variable, but there is
one situation when an automatic assignment happens. If and only if the
input symbol is the only thing inside the conditional of a while
statement (even if disguised as a for(;;) loop), the value is
automatically assigned to the global variable $_, destroying whatever was
there previously. (This may seem like an odd thing to you, but you'll use
the construct in almost every Perls script your write.) The $_ variable is
not implicitly localized. You'll have to put a local $_; before the loop
if you want that to happen.

</quote>

The above site is very handly to have up in your browser while writing
Perl code. At least, it is for me!

--
Maranatha!
John McKown