What is the correct way to break a line of Perl code into two?

Question

$ cat temp.pl
use strict;
use warnings;

print "1\n";
print "hello, world\n";

print "2\n";
print "hello,
world\n";

print "3\n";
print "hello, \
world\n";

$ perl temp.pl
1
hello, world
2
hello,
world
3
hello, 
world
$

To make my code easily readable, I want to restrict the number of columns to 80 characters. How can I break a line of code into two without any side effects?

As shown above, a simple ↵ or \ does not work.

What is the correct way to do this?

Betthezel

Answer 1

In Perl, a carriage return will serve in any place where a regular space does. Backslashes are not used like in some languages; just add a CR.

You can break strings up over multiple lines with concatenation or list operations:

print "this is ",
    "one line when printed, ",
    "because print takes multiple ",
    "arguments and prints them all!\n";
print "however, you can also " .
    "concatenate strings together " .
    "and print them all as one string.\n";

print <<DOC;
But if you have a lot of text to print,
you can use a "here document" and create
a literal string that runs until the
delimiter that was declared with <<.
DOC
print "..and now we're back to regular code.\n";

You can read about here documents in in perldoc perlop.

Weatherbound

Also note that the text returned by the heredoc contains newline characters as they are written whereas the concatenated ones do not – Crinkleroot

Answer 2

One more thing from Perl Best Practices:

Breaking Long lines : Break long expressions before an operator. like

push @steps, $step[-1]
                  + $radial_velocity * $elapsed_time
                  + $orbital_velocity * ($phrase + $phrase_shift)
                  - $test
                  ; #like that

Eductive

I hated that style before reading that book. I'd seen it on mainframe clist scripts, but Damian made a good case about how fast it is to see what's being done. And now I use it all the time. +1 for PBP! – Agglutination

Answer 3

This is because you are inside a string. You can split the strings and concatenate using . as:

print "3\n";
print "hello, ".
"world\n";

Vareck

Answer 4

Use ., the string concatenation operator:

$ perl
print "hello, " .
"world\n";ctrl-d
hello, world
$

Bynum

print was just an example that I used. Is there a general line breaker feature for Perl? – Betthezel

@Lazer: If you want a multi-line string to be single line, use .. Otherwise, perl is free-form and you can put a newline anywhere. – Bynum