vkon has asked for the wisdom of the Perl Monks concerning the following question:

Let's pretend there is no 'f1.txt' file in the current directory and there exists f2.txt one.

Following script: (use strict; is always on) 

open my $fh, "<f1.txt" or do {
    print STDERR "can't open <f1.txt, but nevermind, I'll try f2.txt\n
+";
    open $fh, "<f2.txt" or die "still can't...";
};
print <$fh>; # this gives a warning "read on closed filehandle";

[download]
Last print statement is in a problem: even if f2.txt exists, I see the mentioned warning, but why wasn't failure at nearby open statement ??
If we're seeing different $fh-s, why this was not caught by use strict?

Things work different if I move declaration of $fh above: 

my $fh;
open $fh, "<f1.txt" or do {
    print STDERR "can't open <f1.txt, but nevermind, I'll try f2.txt\n
+";
    open $fh, "<f2.txt" or die "still can't...";
};
print <$fh>; # I see the content of f2.txt here ...

[download]
How this strange scoping explained?

In my currently non-enlightened view, DWIMery is broken.
Can anyone restore DWIMery, please? :)

Replies are listed 'Best First'.
Re: "my $filehandle" scoping strange problem
by Fletch (Bishop) on Apr 14, 2006 at 12:33 UTC

    B::Deparse is your friend in strange syntax corners. 

    $ perl -MO=Deparse,-p,-q
# . . . your first example here
^D
unless (open(my $fh, '<f1.txt')) {
    do {
        print(STDERR "can't open <f1.txt, but nevermind, I'll try f2.t
+xt\n");
        (open($fh, '<f2.txt') or die(q[still can't...]));
    };
}
print(<$fh>);

    [download]

    So you can see now that $fh is scoped to the unless block that's been implicitly created.

    Update: Not that that's not a little wierd, mind you. After looking at it a second time it's slightly surprising.

[reply]
[d/l]
[select]
      Given, as you said, $fh is scoped to the unless block, why the almighty DWIMery allows to use $fh afterwards within a scope of use strict;??
[reply]
[d/l]

        It doesn't. Add a -Mstrict or use strict; and it complains. 

        $ perl -MO=Deparse,-p,-q 
use strict;

open my $fh, "<f1.txt" or do {
    print STDERR "can't open <f1.txt, but nevermind, I'll try f2.txt\n
+";
    open $fh, "<f2.txt" or die "still can't...";
};
print <$fh>;
^D

Global symbol "$fh" requires explicit package name at - line 5.
- had compilation errors.
use strict 'refs';
unless (open(my $fh, '<f1.txt')) {
    do {
        print(STDERR "can't open <f1.txt, but nevermind, I'll try f2.t
+xt\n");
        (open(${'fh'}, '<f2.txt') or die(q[still can't...]));
    };
}
print(<$fh>);

        [download]
[reply]
[d/l]
[select]

Back to Seekers of Perl Wisdom