Hello again,

I was playing with 'do{ }' and found interesting behaviour. Here is a code: 
#!/usr/bin/perl -l

use strict;
use warnings;

my $uninitialized;

print do { $uninitialized };
print do {};
print do { if( 1 ){} };
print do { if( 0 ){} };

print '-' x 10;

print scalar do { $uninitialized };
print scalar do {};
print scalar do { if( 1 ){} };
print scalar do { if( 0 ){} };

[download]
output: 
Use of uninitialized value $uninitialized in print at ./perlmonks_do_u
+nitialized.pl line 8.



0
----------
Use of uninitialized value $uninitialized in print at ./perlmonks_do_u
+nitialized.pl line 15.

Use of uninitialized value in print at ./perlmonks_do_unitialized.pl l
+ine 16.

Use of uninitialized value in print at ./perlmonks_do_unitialized.pl l
+ine 17.

0

[download]
For me it is strange that 'scalar do {};' and 'scalar do { if( 0 ){} };' have different outputs, as the codes look equivalent. Can someone explain a difference in the output?

In reply to printing unitialized value of the 'do BLOCK' by rsFalse

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.