Perl 的 print 如何在默认情况下添加新行？

In Raku (Perl 6) there is, the say function.

Raku (Perl 6) has the say function that automatically appends \n.

You can also use say in Perl 5.10 or 5.12 if you add

use feature qw(say);

to the beginning of your program. Or you can use Modern::Perl to get this and other features.

See perldoc feature for more details.

If Perl 5.10+ is not an option, here is a quick and dirty approximation. It's not exactly the same, since say has some magic when its first arg is a handle, but for printing to STDOUT:

sub say {print @_, "\n"}


say 'hello';

The way you're writing your print statement is unnecessarily verbose. There's no need to separate the newline into its own string. This is sufficient.

print "hello.\n";

This realization will probably make your coding easier in general.

In addition to using use feature "say" or use 5.10.0 or use Modern::Perl to get the built in say feature, I'm going to pimp perl5i which turns on a lot of sensible missing Perl 5 features by default.

Perhaps you want to change your output record separator to linefeed with:

local $\ = "\n";

$ perl -e 'print q{hello};print q{goodbye}' | od -c
0000000    h   e   l   l   o   g   o   o   d   b   y   e
0000014
$ perl -e '$\ = qq{\n}; print q{hello};print q{goodbye}' | od -c
0000000    h   e   l   l   o  \n   g   o   o   d   b   y   e  \n
0000016

Update: my answer speaks to capability rather than advisability. I don't regard adding "\n" at the end of lines to be a "pesky" chore, but if someone really wants to avoid them, this is one way. If I had to maintain a bit of code that uses this technique, I'd probably refactor it out pronto.

You can use the -l option in the she-bang header:

#!/usr/bin/perl -l


$text = "hello";


print $text;
print $text;

Output:

hello
hello

If you're stuck with pre-5.10, then the solutions provided above will not fully replicate the say function. For example

sub say { print @_, "\n"; }

Will not work with invocations such as

say for @arr;

or

for (@arr) {
say;
}

... because the above function does not act on the implicit global $_ like print and the real say function.

To more closely replicate the perl 5.10+ say you want this function

sub say {
if (@_) { print @_, "\n"; }
else { print $_, "\n"; }
}

Which now acts like this

my @arr = qw( alpha beta gamma );
say @arr;
# OUTPUT
# alphabetagamma
#
say for @arr;
# OUTPUT
# alpha
# beta
# gamma
#

The say builtin in perl6 behaves a little differently. Invoking it with say @arr or @arr.say will not just concatenate the array items, but instead prints them separated with the list separator. To replicate this in perl5 you would do this

sub say {
if (@_) { print join($", @_) . "\n"; }
else { print $_ . "\n"; }
}

$" is the global list separator variable, or if you're using English.pm then is is $LIST_SEPARATOR

It will now act more like perl6, like so

say @arr;
# OUTPUT
# alpha beta gamma
#

Here's what I found at https://perldoc.perl.org/perlvar.html:

$\ The output record separator for the print operator. If defined, this value is printed after the last of print's arguments. Default is undef.

You cannot call output_record_separator() on a handle, only as a static method. See IO::Handle.

Mnemonic: you set $\ instead of adding "\n" at the end of the print. Also, it's just like $/ , but it's what you get "back" from Perl.

example:

$\ = "\n";
print "a newline will be appended to the end of this line automatically";