Randy W. Sims wrote:
> I just realized that this might be a little misleading. If you break it
> down to:
>
> my $result = eval $header;
> print $result;
>
> You will get an uninitialized value error. What happens is that
>
> eval $header
>
> is first interpolated to
>
> eval { # File: xyz }
>
> which is executed as perl code. As perl code this is a comment and so
> produces no value, so $result ends up with no value, which is then
> printed in the next line, generating the uninitialized value error.
i think you have the right idea but your example is a little "misleading",
consider:
[panda]# perl -W -le 'print eval "#"'
[panda]# perl -W -le 'print eval {"#"}'
#
similiarly, now consider:
[panda]# perl -W -le 'print eval undef'
Use of uninitialized value in eval "string" at -e line 1.
Use of uninitialized value in print at -e line 1.
[panda]# perl -W -le 'print eval "undef"'
Use of uninitialized value in print at -e line 1.
[panda]# perl -W -le 'print eval {"undef"}'
undef
* we got 2 warnings for the first try because undef is evaluated once and
then returned again to print
* we got 1 warning because undef is returned from eval
* we got no warnings for the last try because the string undef is returned
from eval
* eval{'#'} returns # not undef so your example above will not return undef
* eval EXPR vs. eval BLOCK can be found at perldoc -f eval
david
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