perl - Perl 5 中 `write` 和 `format` 的替代品是什么？

Question

对于简单的输出格式，我倾向于使用 printf，而我在 Perl 4 时代使用 write/format。然而，有时它似乎是每个数据记录的可变输出行数的最简单解决方案。例如

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

my ($lorem, $aprille);

format =
@# ^<<<<<<<<<<<<<<<<<<<<<<<< | ^<<<<<<<<<<<<<<<<<<
$.,$aprille                  , $lorem
   ^<<<<<<<<<<<<<<<<<<<<<<<< | ^<<<<<<<<<<<<<<<<<< ~~
   $aprille                  , $lorem
                             |
.

while(<DATA>) {
  ($aprille, $lorem) = split(/\|/, $_, 2);
  write;
}

__DATA__
WHAN that Aprille with his shoures soote       |Lorem ipsum dolor sit amet,
The droghte of Marche hath perced to the roote,|consectetur adipisicing elit,
And bathed every veyne in swich licour,        |sed do eiusmod tempor
Of which vertu engendred is the flour;         |incididunt ut labore et dolore
Whan Zephirus eek with his swete breeth        |magna aliqua. Ut enim ad minim
Inspired hath in every holt and heeth          |veniam, quis nostrud
The tendre croppes, and the yonge sonne        |exercitation exercitation
Hath in the Ram his halfe cours y-ronne,       |ullamco laboris nisi ut ali-
And smale fowles maken melodye,                |quip ex ea commodo conse-
That slepen al the night with open ye,         |quat. Duis aute irure dolor
So priketh hem nature in hir corages:          |in reprehenderit in volup-
Than longen folk to goon on pilgrimages,       |tate velit esse cillium dol-
And palmers for to seken straunge strondes,    |ore eu fugiat nulla pariatur.
To ferne halwes, couthe in sondry londes;      |Lorem ipsum dolor sit amet,
And specially, from every shires ende          |consectetur adipisicing elit,
Of Engelond, to Caunterbury they wende,        |sed do eiusmod tempor
The holy blisful martir for to seke,           |incididunt ut labore et dolore
That hem hath holpen, whan that they were seke.|magna aliqua. Ut enim ad minim
And now for something completely different. Nice plumage.|Norwegian blue.

生产

   1 WHAN that Aprille with    | Lorem ipsum dolor
     his shoures soote         | sit amet,
                               |
   2 The droghte of Marche     | consectetur
     hath perced to the roote, | adipisicing elit,
                               |
   3 And bathed every veyne in | sed do eiusmod
     swich licour,             | tempor
  ...
  19 And now for something     | Norwegian blue.
     completely different.     |
     Nice plumage.             |

请注意，记录 19 占用了 三 行。

在不使用 write 和 format 的情况下，有什么等效的简洁的 perl5ish 方法？

Answer 1

perl5在perl4的format和write之上增加的主要是formline。还有一些其他的细节，包括 $^A、数字格式和包范围，但这些主要是无关紧要的。当前的格式化指令集仅比 perl4 的多一点:

@    start of regular field
^    start of special field
<    pad character for left justification
|    pad character for centering
>    pad character for right justification
#    pad character for a right justified numeric field
0    instead of first #: pad number with leading zeroes
.    decimal point within a numeric field
...  terminate a text field, show "..." as truncation evidence
@*   variable width field for a multi-line value
^*   variable width field for next line of a multi-line value
~    suppress line with all fields empty
~~   repeat line until all fields are exhausted

其他鲜为人知的增强功能包括支持 LC_NUMERIC 本地，能够使用 {} 分隔的 block 来帮助对齐，以及使用 \r 强制一个真正的换行符。

我仍然不时使用格式。这是我几周前编写的程序的一部分。

sub init_screen() {
    our %Opt;
    my  $cols;

    if ($Opt{width}) {
         $cols  = $Opt{width};
    } 
    elsif (am_unixy()) {
        ($cols) = `stty size 2>&1` =~ /^\d+ (\d+)$/;
    }
    else {
         # FALLTHROUGH to ||= init on next line
    }

    $cols ||= 80; # non-unix or stty error
    $cols  -=  2;

    my $format  = "format STDOUT = \n"
                . '    ^'    . '<' x ($cols-4) . "\n"
                . '$_' . "\n"
                . "       ^" . "<" x ($cols-6) . "~~\n"
                . '$_' . "\n"
                . ".\n"
                . "1;" # for true eval return
                ;

    eval($format) || die;
}

根据当前屏幕宽度动态构建 format 的代码可能更漂亮，但它仍然有用。