Ruby 预定义变量和常量-白红宇

Ruby 预定义变量和常量

阅读量：4229 次

发布时间：2019-05-26

本文共 8380 字，大约阅读时间需要 27 分钟。

其中大部分和 Shell 传递参数很像。既然提到了预定义变量和常量，就顺便把 English 库也说一下，在 Ruby 脚本中使用 English 库，你就可以使用不那么难懂的名称去引用全局变量了（看完下边的例子你就豁然开朗了）。

预定义变量

$_ gets 方法最后读取的字符串

[95] pry(main)> io = File.open("test.txt")=> #
   
    [96] pry(main)> io.gets=> "hello\n"[97] pry(main)> io.gets=> "world\n"[98] pry(main)> $_=> "world\n"[5] pry(main)> $LAST_READ_LINE=> "world\n"

$& 最后一次模式匹配得到的字符串

[100] pry(main)> "12:41 INFO User has logged in.".match(/(\d{2}:\d{2}) (\w+) (.*)/)=> #
   
    [101] pry(main)> $&=> "12:41 INFO User has logged in."[8] pry(main)> $MATCH=> "12:41 INFO User has logged in."

$~ 最后一次模式匹配相关的信息

[100] pry(main)> "12:41 INFO User has logged in.".match(/(\d{2}:\d{2}) (\w+) (.*)/)=> #
   
    [102] pry(main)> $~=> #
    
     [10] pry(main)> $LAST_MATCH_INFO=> #

$` 最后一次模式匹配中匹配部分之前的字符串

[1] pry(main)> "hello world" =~ /ll/=> 2[2] pry(main)> $`=> "he"[14] pry(main)> $PREMATCH=> "he"

$' 最后一次模式匹配中匹配部分之后的字符串

[1] pry(main)> "hello world" =~ /ll/=> 2[3] pry(main)> $'=> "o world"[16] pry(main)> $POSTMATCH=> "o world"

$+ 最后一次模式匹配中最后一个()对应的字符串

[5] pry(main)> "12:41 INFO User has logged in.".match(/(\d{2}:\d{2}) (\w+) (.*)/)=> #
   
    [6] pry(main)> $+=> "User has logged in."[19] pry(main)> $LAST_PAREN_MATCH=> "User has logged in."

$1、$2 最后一次模式匹配中()匹配的字符串（第 n 个 () 对应 $n）

[5] pry(main)> "12:41 INFO User has logged in.".match(/(\d{2}:\d{2}) (\w+) (.*)/)=> #
   
    [7] pry(main)> $1=> "12:41"[8] pry(main)> $2=> "INFO"

$? 最后执行完毕的子进程状态

[9] pry(main)> $?=> #
   
    [21] pry(main)> $CHILD_STATUS => #

$! 最后发生的异常的相关信息

[29] pry(main)> $!=> nil[27] pry(main)> $ERROR_INFO=> nil

$@ 最后发生的异常的相关位置信息

[30] pry(main)> $@=> nil[28] pry(main)> $ERROR_POSITION=> nil

$SAFE 安全级别（默认为 0）

[19] pry(main)> $SAFE(pry):19: warning: $SAFE will become a normal global variable in Ruby 3.0=> 0

$/ 输入数据的分隔符（默认为 “\n”）

[20] pry(main)> $/=> "\n"[22] pry(main)> $INPUT_RECORD_SEPARATOR=> "\n"[23] pry(main)> $RS=> "\n"

$\ 输出数据的分隔符（默认为 nil）

[46] pry(main)> "#{$\}"=> ""[47] pry(main)> $OUTPUT_RECORD_SEPARATOR=> nil[48] pry(main)> $ORS=> nil

$, Array#join 的默认分割字符串（默认为 nil）

[52] pry(main)> "#{$,}"=> ""[53] pry(main)> $OUTPUT_FIELD_SEPARATOR=> nil[54] pry(main)> $OFS=> nil

$; String#split 的默认分割字符串（默认为 nil）

[40] pry(main)> $;[41] pry(main)> $FIELD_SEPARATOR=> nil[42] pry(main)> $FS=> nil

$. 最后读取的文件行号

[25] pry(main)> $.=> 2351[24] pry(main)> $INPUT_LINE_NUMBER=> 2351

$< ARGF 的别名

[26] pry(main)> $<=> ARGF[26] pry(main)> $DEFAULT_INPUT=> ARGF

$> print、puts、p 等的默认输出位置（默认为 STDOUT）

[34] pry(main)> $>=> #
   
    
     >[29] pry(main)> $DEFAULT_OUTPUT=> #
     
      
       >

$0 $PROGRAM_NAME 的别名

[32] pry(main)> $0=> "pry"[30] pry(main)> $PROGRAM_NAME=> "pry"

$* ARGV 的别名

[35] pry(main)> $*=> [][33] pry(main)> $ARGV=> []

$$ 当前执行中的 Ruby 的进程 ID

[36] pry(main)> $$=> 5126[34] pry(main)> $PROCESS_ID=> 5126

$: $LOAD_PATH 的别名

[37] pry(main)> $:=> ["/usr/local/ruby-2.7.1/lib/ruby/gems/2.7.0/gems/coderay-1.1.3/lib", "/usr/local/ruby-2.7.1/lib/ruby/gems/2.7.0/gems/method_source-1.0.0/lib", "/usr/local/ruby-2.7.1/lib/ruby/gems/2.7.0/gems/pry-0.13.1/lib", "/usr/local/ruby-2.7.1/lib/ruby/site_ruby/2.7.0", "/usr/local/ruby-2.7.1/lib/ruby/site_ruby/2.7.0/x86_64-linux", "/usr/local/ruby-2.7.1/lib/ruby/site_ruby", "/usr/local/ruby-2.7.1/lib/ruby/vendor_ruby/2.7.0", "/usr/local/ruby-2.7.1/lib/ruby/vendor_ruby/2.7.0/x86_64-linux", "/usr/local/ruby-2.7.1/lib/ruby/vendor_ruby", "/usr/local/ruby-2.7.1/lib/ruby/2.7.0", "/usr/local/ruby-2.7.1/lib/ruby/2.7.0/x86_64-linux"][62] pry(main)> $LOAD_PATH=> ["/usr/local/ruby-2.7.1/lib/ruby/gems/2.7.0/gems/coderay-1.1.3/lib", "/usr/local/ruby-2.7.1/lib/ruby/gems/2.7.0/gems/method_source-1.0.0/lib", "/usr/local/ruby-2.7.1/lib/ruby/gems/2.7.0/gems/pry-0.13.1/lib", "/usr/local/ruby-2.7.1/lib/ruby/site_ruby/2.7.0", "/usr/local/ruby-2.7.1/lib/ruby/site_ruby/2.7.0/x86_64-linux", "/usr/local/ruby-2.7.1/lib/ruby/site_ruby", "/usr/local/ruby-2.7.1/lib/ruby/vendor_ruby/2.7.0", "/usr/local/ruby-2.7.1/lib/ruby/vendor_ruby/2.7.0/x86_64-linux", "/usr/local/ruby-2.7.1/lib/ruby/vendor_ruby", "/usr/local/ruby-2.7.1/lib/ruby/2.7.0", "/usr/local/ruby-2.7.1/lib/ruby/2.7.0/x86_64-linux"]

$" $LOADED_FEATURES 的别名

[38] pry(main)> $"=> ["enumerator.so", "thread.rb", "rational.so", "complex.so", "ruby2_keywords.rb", "/usr/local/ruby-2.7.1/lib/ruby/2.7.0/x86_64-linux/enc/encdb.so", "/usr/local/ruby-2.7.1/lib/ruby/2.7.0/x86_64-linux/enc/trans/transdb.so", "/usr/local/ruby-2.7.1/lib/ruby/2.7.0/x86_64-linux/rbconfig.rb", "/usr/local/ruby-2.7.1/lib/ruby/2.7.0/rubygems/compatibility.rb", "/usr/local/ruby-2.7.1/lib/ruby/2.7.0/rubygems/defaults.rb",[63] pry(main)> $LOADED_FEATURES=> ["enumerator.so", "thread.rb", "rational.so", "complex.so", "ruby2_keywords.rb", "/usr/local/ruby-2.7.1/lib/ruby/2.7.0/x86_64-linux/enc/encdb.so", "/usr/local/ruby-2.7.1/lib/ruby/2.7.0/x86_64-linux/enc/trans/transdb.so", "/usr/local/ruby-2.7.1/lib/ruby/2.7.0/x86_64-linux/rbconfig.rb", "/usr/local/ruby-2.7.1/lib/ruby/2.7.0/rubygems/compatibility.rb", "/usr/local/ruby-2.7.1/lib/ruby/2.7.0/rubygems/defaults.rb",

$DEBUG 指定 DEBUG 模式的标识

[4] pry(main)> $DEBUG=> false

$FILENAME ARGF 当前在读的文件名

[6] pry(main)> $FILENAME=> "-"

$LOAD_PATH 执行 require 读取文件时搜索的目录名数组

[7] pry(main)> $LOAD_PATH=> ["/usr/local/ruby-2.7.1/lib/ruby/gems/2.7.0/gems/coderay-1.1.3/lib", "/usr/local/ruby-2.7.1/lib/ruby/gems/2.7.0/gems/method_source-1.0.0/lib", "/usr/local/ruby-2.7.1/lib/ruby/gems/2.7.0/gems/pry-0.13.1/lib", "/usr/local/ruby-2.7.1/lib/ruby/site_ruby/2.7.0", "/usr/local/ruby-2.7.1/lib/ruby/site_ruby/2.7.0/x86_64-linux", "/usr/local/ruby-2.7.1/lib/ruby/site_ruby", "/usr/local/ruby-2.7.1/lib/ruby/vendor_ruby/2.7.0", "/usr/local/ruby-2.7.1/lib/ruby/vendor_ruby/2.7.0/x86_64-linux", "/usr/local/ruby-2.7.1/lib/ruby/vendor_ruby", "/usr/local/ruby-2.7.1/lib/ruby/2.7.0", "/usr/local/ruby-2.7.1/lib/ruby/2.7.0/x86_64-linux"]

$stdin 标准输入（默认为 STDIN）

[8] pry(main)> $stdin=> #
   
    
     >

$stdout 标准输出（默认为 STDOUT）

[9] pry(main)> $stdout=> #
   
    
     >

$stderr 标准错误输出（默认为 STDERR）

[10] pry(main)> $stderr=> #
   
    
     >

$VERBOSE 指定冗长模式的标识（默认为 nil）

[11] pry(main)> $VERBOSE=> false

$PROGRAM_NAME 当前执行中的 Ruby 脚本别名

[12] pry(main)> $PROGRAM_NAME=> "pry"

$LOADED_FEATURES require 读取的类库名一览表

[13] pry(main)> $LOADED_FEATURES=> ["enumerator.so", "thread.rb", "rational.so", "complex.so", "ruby2_keywords.rb", "/usr/local/ruby-2.7.1/lib/ruby/2.7.0/x86_64-linux/enc/encdb.so", "/usr/local/ruby-2.7.1/lib/ruby/2.7.0/x86_64-linux/enc/trans/transdb.so", "/usr/local/ruby-2.7.1/lib/ruby/2.7.0/x86_64-linux/rbconfig.rb", "/usr/local/ruby-2.7.1/lib/ruby/2.7.0/rubygems/compatibility.rb", "/usr/local/ruby-2.7.1/lib/ruby/2.7.0/rubygems/defaults.rb", "/usr/local/ruby-2.7.1/lib/ruby/2.7.0/rubygems/deprecate.rb", "/usr/local/ruby-2.7.1/lib/ruby/2.7.0/rubygems/errors.rb", "/usr/local/ruby-2.7.1/lib/ruby/2.7.0/rubygems/version.rb", "/usr/local/ruby-2.7.1/lib/ruby/2.7.0/rubygems/requirement.rb", "/usr/local/ruby-2.7.1/lib/ruby/2.7.0/rubygems/platform.rb", "/usr/local/ruby-2.7.1/lib/ruby/2.7.0/rubygems/basic_specification.rb", "/usr/local/ruby-2.7.1/lib/ruby/2.7.0/rubygems/stub_specification.rb",

预定义常量

ARGF

[1] pry(main)> ARGF=> ARGF

ARGV

[2] pry(main)> ARGV=> []

ENV

[5] pry(main)> ENV=> {"CLASSPATH"=>":/usr/lib/jvm/java/lib:/usr/lib/jvm/java/jre/lib", "COLUMNS"=>"119", "HISTCONTROL"=>"ignoredups", "HISTSIZE"=>"1000", "HOME"=>"/root", "HOSTNAME"=>"master", "JAVA_HOME"=>"/usr/lib/jvm/java", "JENKINS_HOME"=>"/var/lib/jenkins/", "JRE_HOME"=>"/usr/lib/jvm/java/jre", "LANG"=>"en_US.UTF-8", "LESSOPEN"=>"||/usr/bin/lesspipe.sh %s", "LINES"=>"18", "LOGNAME"=>"root",  ...

RUBY_COPYRIGHT

[8] pry(main)> RUBY_COPYRIGHT=> "ruby - Copyright (C) 1993-2020 Yukihiro Matsumoto"

RUBY_DESCRIPTION

[9] pry(main)> RUBY_DESCRIPTION=> "ruby 2.7.1p83 (2020-03-31 revision a0c7c23c9c) [x86_64-linux]"

RUBY_ENGINE

[10] pry(main)> RUBY_ENGINE=> "ruby"

RUBY_PATCHLEVEL

[12] pry(main)> RUBY_PATCHLEVEL=> 83

RUBY_PLATFORM

[13] pry(main)> RUBY_PLATFORM=> "x86_64-linux"

RUBY_RELEASE_DATE

[14] pry(main)> RUBY_RELEASE_DATE=> "2020-03-31"

RUBY_VERSION

[15] pry(main)> RUBY_VERSION=> "2.7.1"

STDERR

[16] pry(main)> STDERR=> #
   
    
     >

STDIN

[17] pry(main)> STDIN=> #
   
    
     >

STDOUT

[18] pry(main)> STDOUT=> #
   
    
     >

self

[1] pry(main)> self=> main

FILE

[2] pry(main)> __FILE__=> "(pry)"

LINE

[3] pry(main)> __LINE__=> 3

ENCODING

[4] pry(main)> __ENCODING__=> #

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