How do I read paragraphs at a time with Perl?

When开发者_C百科 I write

#!/usr/bin/perl -w
use strict;

while( <DATA> ) {
    print "\n-------------------------\n\n";
    print;
    <>;
}

after each "return" I get one line.

Why don't I get with the next script after each "return" one paragraph?

#!/usr/bin/perl -w
use strict;

local $/ = "";

while( <DATA> ) {
    print "\n-------------------------\n\n";
    print;
    <>;
}

__DATA__
line one
line two
line three
line four
line five

line six
line seven
line eigth
line nine

line ten
line eleven
line twelve

In your first script, with the $/ variable set to default "\n", the <DATA> will only return one line at a time.

I believe the second script does what you want, it's just that <> won't terminate the read on a 'return' but rather on a <ctrl-d> due to your $/ setting (as someone else pointed out <> reads from STDIN but I think you already know that and are using it to regulate the output).

If you really want to regulate the output with 'return' then you need to do more with $/ in the loop.

while( <DATA> ) {
    print "\n-------------------------\n\n";
    print;
    $/ = "\n"; # default so that the following terminates the read on 'return'
    <>;
    $/ = ""; 
}   

I guess you're expecting this line

local $/ = "";

to change the behaviour of

<DATA>

to keep reading until the end of the data.

But in fact it takes something like this

{
    local $/;  # $/ becomes undef in this block
    ...
}

to enable slurp mode (and to contain that mode to the scope inside the {curlys}).

In effect it's saying "forget about thinking of newlines as the end-of-record marker",

Besides that... there's a tie fighter in your code!

while( <DATA> ) {
    print "\n-------------------------\n\n";
    print;
    <>;    # <-- Feel the power of the DARK SIDE!!!
}

This little guy will read from STDIN, not from DATA - is that really what you want?

Using <> that way (interactively) in paragraph mode is going to be confusing. It won't return when you hit "return"; instead, it will read until it gets a non empty line (the start of a paragraph), then read until it gets an empty line (the end of that paragraph), then continue reading until it gets a non-empty line (the start of the following paragraph - which will be buffered, not returned) so it knows that it's discarded any extra empty lines.

Perhaps you should be using:

local $/ = "\n"; <>

at the end of your loop instead. Or maybe POSIX::getchar().