红宝石 |预定义变量和常量
Ruby 预定义变量
Ruby 包含范围广泛的预定义变量。每个预定义变量都有自己的规范。您可以使用预定义变量来执行特定任务,例如在处理解释器参数或正则表达式时。 Ruby 中的预定义变量列表如下所示:
Variables | Description |
---|---|
$! | It holds the exception information message set by the last ‘raise’. Alias of $ERROR_INFO. |
$@ | It holds an array of the backtrace of the last exception raised. Alias of $ERROR_POSITION. |
$/ | The input record separator, by default newline. If it is set to nil then the whole file will be read at once. Alias of $INPUT_RECORD_SEPARATOR. |
$\ | The output separator for the print and IO#write, nil by default. Alias of $OUTPUT_RECORD_SEPARATOR |
$, | The output field separator for the print and default separator for Array#join. Alias of $OUTPUT_FIELD_SEPARATOR. |
$; | It is the default separator for String#split. Alias of $FIELD_SEPARATOR. |
$. | It holds the current input line number read from the last file. Alias of $INPUT_LINE_NUMBER. |
$< | An object that gives access to the concatenation of the content of all the files given as a command line argument or $stdin. Alias of $DEFAULT_INPUT. |
$> | It is the destination of output for kernel.print and kernel.printf, the default value is $stdout. Alias of $DEFAULT_OUTPUT. |
$& | The string matched by the last pattern match. Alias of $MATCH. |
$` | The string to the left of the last pattern match. Alias of $PREMATCH. |
$’ | The string to the right of the last pattern match. Alias of $POSTMATCH. |
$+ | The string correlated to the last matched group in the last successful pattern matched. Alias of $LAST_PAREN_MATCH. |
$1-$9 | The string matched in the nth group of the last successful pattern matched. |
$_ | The last input line read by get or readline in the current scope. It is a local variable. Alias of $LAST_READ_LINE. |
$~ | It holds the information about the last match in the current scope. It is a local variables. Alias of $LAST_MATCH_INFO. |
$-p | It is true if option -p is set (loop mode is on). It is read-only variable. |
$-l | It is true if option -l is set (line-ending process is on). It is read-only variable. |
$-i | This variable hold the extension if in-place-edit mode is set otherwise nil. |
$-a | It is true if option -a is set (autosplit mode is one). It is read-only variable. |
$-d | The level of -d is switch. Alias of $DEBUG. |
$-v | The verbose flag. It is set by the -v switch. Alias of $VERBOSE. |
$-K | The character encoding of the source code. Alias of $KCODE. |
$0 | It contains the name of the script being executed. |
$$ | The process number of the current Ruby program being executed. Alias of $PROCESS_ID. |
$? | The status of the last child process terminated. Alias of $CHILD_STATUS. |
$: | Load paths for programs and binary module by load or required. Alias of $LOAD_PATH. |
$FILENAME | The name of current input file reads from $<. Same as $<.filename. |
$stderr | Current standard error output. |
$stdin | Current standard input. |
$stdout | Current standard output. |
$= | Flag for case-sensitive, nil by default.Alias of $IGNORECASE |
$* | Command line argument given for the program, also known as ARGV.Alias of ARGV. |
$” | Array contains the module name loaded by require.Alias of $LOAD_FEATURES. |
例子:
# Ruby program to illustrate the
# use of pre-defined Variables
# Using '$0' To know about the
# script name
puts "Script_name: ",$0;
# Using ' #{$$}' to know about the total
# number of process in the script
puts "Total number of process in this script: #{$$}"
# Using $; as default separator
# for String#split.
a = "1,2,3,4,5,6,7"
$; = ","
p a.split
# Pattern matching
"Welcome to GeeksforGeeks Portal!" =~ /Geeks/
# use to print the string to the
# left of the last pattern match
p $`
# use to print the string matched
# by the last pattern match
p $&
# use to print the string to the
# right of the last pattern match
p $'
输出:
Script_name:
/var/www/service/usercode/969513068/source.rb
Total number of process in this script: 3950
["1", "2", "3", "4", "5", "6", "7"]
"Welcome to "
"Geeks"
"forGeeks Portal!"
Ruby 预定义常量
Ruby 包含许多预定义的常量。预定义常量列表如下所示:
Constant Name | Description |
---|---|
TRUE | Equivalent to true. |
FALSE | Equivalent to false. |
NIL | Equivalent to nil. |
STDIN | Standard input and default value of $stdin. |
STDOUT | Standard output and default value of $stdout. |
STDERR | Standard output error and default value of $stderr. |
RUBY_VERSION | A string shows the version of Ruby interpreter. |
RUBY_PLATFORM | A string shows the platform of Ruby interpreter. |
RUBY_RELEASE_DATE | A string shows the release date of Ruby interpreter. |
DATA | The file object of the program, pointing just after the __END__. And not defined if __END__ is not present in the program. |
ARGV | An array holds the command-line arguments passed to the program. Alias of $*. |
ARGF | An object that gives the access to the virtual concatenation of files passed as command-line arguments. Alias of $<. |
ENV | It is a hash-like object, contains current environment variables. |
注意:建议使用 true、false 和 nil,因为 TRUE、FALSE 和 NIL 是向后兼容的。
例子:
# Ruby program to illustrate
# pre-defined Constants
# To know about Ruby Version
a = RUBY_VERSION
puts "Current Version: #{a}"
# To Know about Ruby Platform
b = RUBY_PLATFORM
puts "Platform of Ruby: #{b}"
# To know about Ruby Release Date
c = RUBY_RELEASE_DATE
puts "Release date of Ruby: #{c}"
输出:
Current Version: 2.3.1
Platform of Ruby: x86_64-linux-gnu
Release date of Ruby: 2016-04-26