print "$var\n" or print $var, "\n"

What is the difference between

my @a = (1) x 1024; print $_, "\n" for @a;
[download]

and

my @b = (1) x 1024; print "$_\n" for @b;
[download]

Answer:

About 14kb:

#!/usr/bin/perl

use strict;
use warnings;

use Devel::Size 'total_size';

my @a = (1) x 1024;
my @b = (1) x 1024;

open my $fh, "> /dev/null" or die;
print $fh $_, "\n" for @a;
print $fh "$_\n" for @b;
close $fh;

print total_size(\@a), "\n";
print total_size(\@b), "\n";

__END__
24636
38972
[download]

That's because the "$_\n" causes stringification, and the $_, "\n" doesn't.

Comment on print "$var\n" or print $var, "\n" Select or Download Code

Replies are listed 'Best First'.
Re: print "$var\n" or print $var, "\n" by Mr. Muskrat (Canon) on Feb 17, 2005 at 13:06 UTC
The difference is in the magic that makes Perl, well, Perl. Scalars can be numeric or "strings". When you store an integer in a scalar it's stored as an IV. When you use that scalar in string context it gets stringified. The scalar is modified behind the scenes to be a PVIV with pointers to an IV and PV. `#!/usr/bin/perl use strict; use warnings; use Devel::Peek; my @a = (1) x 1024; my @b = (1) x 1024; open my $fh, "> /dev/null" or die; print $fh $_, "\n" for @a; print $fh "$_\n" for @b; close $fh; Dump $a[0]; Dump $b[0];` [download] Update: Fixed wording of fourth sentence.	[reply] [d/l]
Re: print "$var\n" or print $var, "\n" by kscaldef (Pilgrim) on Feb 17, 2005 at 17:59 UTC
Another difference: "$_\n" will always DWYW. However, if some naughty person modified $, then $_,"\n" might do something unexpected.	[reply]
Re^2: print "$var\n" or print $var, "\n" by Fletch (Bishop) on Feb 17, 2005 at 20:07 UTC
Unless of course someone's mucked with `$\` . . . `$ perl -le '$\="wubba\n"; print "foo\n"' foo wubba` [download] Update: Good point about `printf` below. There's also `syswrite`, for that matter.	[reply] [d/l] [select]
Re^3: print "$var\n" or print $var, "\n" by Animator (Hermit) on Feb 17, 2005 at 20:48 UTC
A 'fix' for that: printf :)	[reply]
Re^3: print "$var\n" or print $var, "\n" by Aristotle (Chancellor) on Feb 19, 2005 at 05:26 UTC
You can always localize it if you're afraid of ghosts. Makeshifts last the longest.	[reply]
Re: print "$var\n" or print $var, "\n" by davido (Cardinal) on Feb 17, 2005 at 17:02 UTC
:) Of course it depends on what you call a "difference". From another perspective, the difference is: '`,`' It all depends on how you look at the world. Dave	[reply] [d/l]