Perl - さまざまな制御構造(真偽値、未定義値とdefined-or演算子(//))

初めてのPerl 第6版
Randal L. Schwartz,
Tom Phoenix, brian d foy 共著
近藤 嘉雪 翻訳

開発環境

• OS X Lion - Apple(OS)
• TextWrangler(Text Editor) (BBEditの機能制限無料版、light版)
• Script言語:Perl

『初めてのPerl 第6版』(Randal L. Schwartz, Tom Phoenix, brian d foy 共著、近藤 嘉雪 訳、オライリー・ジャパン、2012年、ISBN978-4-87311-567-2) の10章(さまざまな制御構造)、10.11(練習問題)3を解いてみる。

その他参考書籍

• プログラミングPerl〈VOLUME1〉
• プログラミングPerl〈VOLUME2〉

3.

コード(TextWrangler)

sample.pl

#!/usr/bin/env perl
use strict;
use warnings;
use utf8;
use 5.012;
binmode STDOUT, ':utf8';
binmode STDIN, ':utf8';

# この3つの環境変数の値がdefined - or演算子でちゃんと設定されるか確認
$ENV{ZERO} = 0;
$ENV{UNDEF} = undef;
$ENV{EMPTY} = '';

my $cols = 0;
for(keys %ENV){
  $cols = length $_ if length $_ > $cols;
}

for(sort keys %ENV){
  printf "%-${cols}s %s\n", $_, $ENV{$_} // "undefined value";
}

入出力結果(Terminal)

$ ./sample.pl
Apple_PubSub_Socket_Render /tmp/launch-DikxEZ/Render
Apple_Ubiquity_Message     /tmp/launch-JWCTOv/Apple_Ubiquity_Message
COMMAND_MODE               unix2003
DEBUG                      0
DISPLAY                    /tmp/launch-cdiRix/org.x:0
HOME                       /Users/kamimura
LANG                       ja_JP.UTF-8
LOGNAME                    kamimura
OLDPWD                     /Users/kamimura/documents/c
PATH                       /Users/kamimura/pear/bin/:/opt/local/bin:/opt/local/sbin:/usr/local/mysql/bin/:/Library/Frameworks/Python.framework/Versions/3.2/bin:/Library/Frameworks/Python.framework/Versions/Current/bin:/usr/bin:/bin:/usr/sbin:/sbin:/usr/local/bin:/usr/X11/bin:/usr/local/MacGPG2/bin
PWD                        /Users/kamimura/documents/perl
SECURITYSESSIONID          186a6
SHELL                      /bin/bash
SHLVL                      1
SSH_AUTH_SOCK              /tmp/launch-A2ghkG/Listeners
TERM                       xterm-256color
TERM_PROGRAM               Apple_Terminal
TERM_PROGRAM_VERSION       303.2
TERM_SESSION_ID            BFEDC242-4ACE-4EEF-8617-4B530405F277
TMPDIR                     /var/folders/1v/dvc2tljs2_z3zqn56g_29rl00000gn/T/
USER                       kamimura
_                          ./sample.pl
__CF_USER_TEXT_ENCODING    0x1F5:0:0
DEBUG 0
kamimuras-MacBook-Pro:perl kamimura$ ./sample.pl
Apple_PubSub_Socket_Render /tmp/launch-DikxEZ/Render
Apple_Ubiquity_Message     /tmp/launch-JWCTOv/Apple_Ubiquity_Message
COMMAND_MODE               unix2003
DEBUG                      0
DISPLAY                    /tmp/launch-cdiRix/org.x:0
EMPTY                      
HOME                       /Users/kamimura
LANG                       ja_JP.UTF-8
LOGNAME                    kamimura
OLDPWD                     /Users/kamimura/documents/c
PATH                       /Users/kamimura/pear/bin/:/opt/local/bin:/opt/local/sbin:/usr/local/mysql/bin/:/Library/Frameworks/Python.framework/Versions/3.2/bin:/Library/Frameworks/Python.framework/Versions/Current/bin:/usr/bin:/bin:/usr/sbin:/sbin:/usr/local/bin:/usr/X11/bin:/usr/local/MacGPG2/bin
PWD                        /Users/kamimura/documents/perl
SECURITYSESSIONID          186a6
SHELL                      /bin/bash
SHLVL                      1
SSH_AUTH_SOCK              /tmp/launch-A2ghkG/Listeners
TERM                       xterm-256color
TERM_PROGRAM               Apple_Terminal
TERM_PROGRAM_VERSION       303.2
TERM_SESSION_ID            BFEDC242-4ACE-4EEF-8617-4B530405F277
TMPDIR                     /var/folders/1v/dvc2tljs2_z3zqn56g_29rl00000gn/T/
UNDEF                      undefined value
USER                       kamimura
ZERO                       0
_                          ./sample.pl
__CF_USER_TEXT_ENCODING    0x1F5:0:0
$