in reply to Splitting in while loop

Summary

  1. RULE: while doesn't assign any variables (like foreach ) it's a boolean check alike if(CONDITION) { DO LOOP }
  2. Some operations assign automatically to some vars (side-effect) and return true on success. E.g. regexes setting $1 etc can be combined with a boolean check.
  3. Some like <FH> do this only inside while(<FH>) context for exceptinal DWIM

Cheers Rolf
(addicted to the Perl Programming Language :)
Wikisyntax for the Monastery

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Re^2: Splitting in while loop
by perlfan (Parson) on Oct 12, 2021 at 16:09 UTC
    In non-slurp mode, this works via assignment using the diamond operator (<>) - or just the same if you open an file handle, $FH: 
    # test.pl
while (my $line = <>) {
  chomp $line;
  print qq{$line\n}; # yes I know, pointless use of chomp
}

    [download]
    > perl test.pl < test.pl
# test.pl
while (my $line = <>) {
  chomp $line;
  print qq{$line\n}; # yes I know, pointless use of chomp
}

    [download]
    Similarly, you could do something destructive with pop or shift, like, 
    while (my $item = pop @my_array) {
  # do stuff with $item
}

    [download]
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[select]
      while (my $line = <>) ... Similarly, ... while (my $item = pop @my_array)
      use warnings;
use strict;

while (my $line = <DATA>) {
    chomp $line;
    print "<$line>\n";
}

my @array = ("Foo","0","Bar");
while (my $item = pop @array) {
    print "[$item]\n";
}

__DATA__
Hello
0

World

      [download]

      Outputs:

      <Hello>
<0>
<>
<World>
[Bar]

      [download]

      I'd call that a pretty serious caveat. As per I/O Operators, the first is equivalent to while ( defined( my $line = <> ) ), and readline returns undef at EOF, while the second one will stop at any false value, and arrays can contain undefs too.

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