endless loop while .=

[Anonymous Monk]

Fellow Monks, consider the following code

#!/usr/bin/perl
use warnings;
use strict;

my $content;

open(IN, "<", $ARGV[0]) or die $!;
while ( $content .= <IN> ) {
  print $content;
};
close(IN) or die $!;

Can someone explain in laymans words why .= causes an endless while loop?

[almut]

...because $content is accumulating the input. In other words, it isn't empty/false when the while loop has reached the end of the input, so the while loop keeps running.

[Anonymous Monk]

Thank you.

[Marshall]

See explanation by almut - while() is testing true/false of the statement, not status of <IN>. Here is small mod to your code that avoids the problem.

#!/usr/bin/perl
use warnings;
use strict;

my $content;

open(IN, "<", $ARGV[0]) or die $!;
while ( <IN> ) {
  print $content.= $_;
};
close(IN) or die $!;

[apl]

You can always append a Null ...