Introduction to the built-in special variables for Perl _perl

Special variable of regular expression

1, $n: The nth substring containing the last pattern match
2, $&: Previous successful pattern matching string
3, $ ': previous match successful substring before
4, $ ': After the substring of the previous match succeeded
5, $+: The previous use of parentheses pattern matching the string.

Second, the file handle special variables

1, $| : If set to zero, the function fflush is called automatically after each call to the function write or print, and the written content is written back to the file
2, $%: Current output page number
3, $=: The current length of each page
4, $-: The number of rows remaining on the current page
5, $~: The name of the current report output format. The default value is the file handle name.
6, $^: The name of the current report output header format. The default value is a file handle name with the suffix "_top".

Third, global special variables

1, $_ and $arg: Default input and pattern matching content. If you do not specify a variable to receive input or a string that performs a pattern match
2, $. and $nr: The current line number of the previous read file handle
3, $/and $rs: Enter the record separator, the default is the new line character. If you use the undef variable, you will read the end of the file
4, $, $ofs: output domain separator.
5, $\ and $ors: Output record separator
6, $:: Break the character, the default is "n" three characters
7, $! : The numeric value of this variable is the errno value, and the string value is the corresponding system error string
8. $@: The error message for the eval command. If empty, the last eval command executed successfully
9. $$: Process number running the current Perl script program
10, $<: The actual user number of the current process
11. $>: Valid user number for current process
12, $ (: Actual group user number of the current process)
13, $): Valid group user number for current process
14, $[: Array array of the first element of the subscript, default is 0
15, $]:P version number of Erl
16. $ARGV: Save the current file name when using "< >" to read the file

Four, global special array variables

1, @ARGV: Save command Line parameters
2, @INC: Save directory to find Perl programs
3, @_: In the subroutine, this array variable contains the parameters passed to the subroutine
4.%inc: Hash list%inc contains all the files contained in do or require statements. The keyword is the file name, and the value is the path to the file.
5,%env: Contains the current environment variables

Five, global special file handle

1. ARGV: A special file handle that traverses all file names in the array variable @argv
2, STDERR: standard error output handle
3. STDIN: Standard input handle
4, STDOUT: standard output handle

Perl Built-in variables

$-the number of lines that the current page can print, part of the Perl format system
$! Returns an error number or error string based on the context content
$ "List separator
$# the default digital output format when printing numbers
$$ The process ID of the Perl interpreter
$% Current page number of the current output channel
$& a string that matches the previous format
$ (Group ID of the current process
$) Valid group ID for the current process
$* Set 1 to handle multiple-line formatting. Now replace it with the/s and/M modifiers.
$, Current output field separator
$. Current input line number of the last read file
$/current input record delimiter, default is new row
$: Character settings, subsequent strings will be separated to fill contiguous fields.
$; The delimiter to use when simulating a multidimensional array.
$? Returns the status of the previous external command
$@ The Perl interpreter returns an error message from the eval statement
The index number of the first element in the $[array
$ separator for current output record
$] Sub version number of the Perl interpreter
$^ the top page output format name of the current channel
$^a variables used to save formatted data before printing
$^d the value of the debug flag
$^e operating system extended error messages in non-UNIX environments
$^f Maximum file Bundle Descriptor value
$^h the compiler-activated syntax check state
$^i the value of the built-in control editor
$^l a paper-feed break sent to the output channel
$^m the size of the standby memory pool
$^o Operating system name
$^P specifies the internal variable for the current debug value
$^r the last evaluation result of a regular expression block
$^s Current Interpreter State
$^t from the beginning of the new century, the pace of the beginning of the time calculated in seconds
The current value of the $^W warning switch
$^x perl binary Executable code name
$_ default input/output and format matching space
$| Controls the buffering of the currently selected output file handle
$~ the name of the current report format
$ ' string before matching information in the previous format
$ ' string after matching information in the previous format
$+ the last bracket that matches the last regular expression search format
$< The true ID of the user who is currently executing the interpreter
$ contains the parentheses result corresponding to the last matched regular expression
$= the number of lines that the current page can print
$> A valid user ID for the current process
$ contains the filename of the script being executed
$ARGV the current file name when read from the default file handle
%ENV Environment Variables List
%inc a list of files contained by do or require
%sig signal list and how to handle it
@_ a list of parameters to a subroutine
@ARGV a list of command line arguments passed to the script
@INC List of directories to search for when importing a module
$-[0] and $+[0] represent the starting and terminating positions of the current matching regular expression in the matched string.