slurping __DATA__

[LanceDeeply]

I know this code:

my $data = do { local $/; <DATA> };

slurps the __DATA__ section into my scalar $data, but what is perl doing in that do loop?

    my $data = do
    {
        local $/; # localize RS?
        <DATA>    # evaluate <DATA> in scalar context ?
    }

what's happenning in there?

[jeffa]

do is "not really a function". It is a block that has a seperate scope from wherever it was called from. This allows you to localize $/ so that when execution leaves our "temporary" scope, $/ will be what it was before it was changed.

If you look up $/ in perlvar, you will see

   You may set it to a multi-character
   string to match a multi-character terminator, or
   to "undef" to read through the end of file.

Finally, <DATA> returns the next line from the filehandle DATA, and since $/ is undefined, the entire contents of the file are returned and "caught" in a scalar.
UPDATE: i should add that this is one of those few cases where local is a good choice. For example,

local $/;

Is essentially the same as

local $/ = undef;

Which is not the same as

$/ = undef;

Even though that last snippet will be contained inside a do block ... $/ will still be undef afterwards. Try this - make two files foo.txt and bar.txt and run this:
Read more... (454 Bytes)

jeffa

L-LL-L--L-LL-L--L-LL-L--
-R--R-RR-R--R-RR-R--R-RR
B--B--B--B--B--B--B--B--
H---H---H---H---H---H---
(the triplet paradiddle with high-hat)

[LanceDeeply]

Thanks!

I did read perldoc perlvar but I didnt know that local $/; was undef-ing it for the do's block context. I'll have to go brush up on local, 'cause I never use it.

[jeffa]

For the record, tye was the first one to show me that trick. (tye++ yet again) But .... please be careful with local - reserve its use for temporarily resetting Perl's built-in variables. Don't use it on, well, anything else. ;) Read Anti-snippet (or, "local" considered dangerous to fools") if you haven't already.

And you are most welcome. :)

jeffa

L-LL-L--L-LL-L--L-LL-L--
-R--R-RR-R--R-RR-R--R-RR
B--B--B--B--B--B--B--B--
H---H---H---H---H---H---
(the triplet paradiddle with high-hat)

[Zeroth]

See: perldoc -f do
And read the part about "do BLOCK". That should explain it quite well.