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Re: slurping __DATA__

by jeffa (Chancellor)
on Aug 08, 2003 at 14:17 UTC ( #282187=note: print w/ replies, xml ) Need Help??


in reply to slurping __DATA__

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:
# print entire file open FH,'foo.txt'; my $foo = do {$/ = undef;<FH>}; print $foo; # print only first line open FH,'bar.txt'; my $bar = <FH>; print $bar;
Then go back and add local to the do block.

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)


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Re: Re: slurping __DATA__
by LanceDeeply (Chaplain) on Aug 08, 2003 at 14:44 UTC
    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.

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