Introduction to special built-in variables of perl

I. Special variables of Regular Expressions

1. $ n: contains the nth substring of the last pattern match.
2. $ &: String matched in the previous successful mode
3. $ ': Content Before the successful substring
4. $ ': content after the child string that was matched successfully before
5. $ +: the string that was previously matched using the brackets pattern.

Ii. file handle special Variables

1. $ |: if it is set to zero, the fflush function is automatically called every time the function write or print is called, and the written content is written back to the file.
2. $ %: current output page number
3. $ =: current length of each page
4. $-: number of remaining lines on the current page
5. $ ~ : Name of the current report output format. The default value is the file handle name.
6. $ ^: name of the current report output Header Format. The default value is the file handle name with the suffix "_ TOP.

Iii. Global Special Variables

1. $ _ and $ ARG: Default Input and mode matching content. If you do not specify to receive input variables or strings that match the execution mode
2. $. and $ NR: current row number of the file handle read before
3. $/and $ RS: the input record delimiter. The default Delimiter is a new line character. If you use the undef variable, it will be read to the end of the file.
4. $, $ OFS: Output domain separator.
5. $ \ and $ ORS: Output record Separator
6. $: The line break character. The default value is "\ n -".
7. $! : The numeric value of this variable is the value of errno, and the string value is the corresponding system error string
8. $ @: error message of the command eval. If it is null, the last eval command is successfully executed.
9. $: Process Number of the current Perl script program
10. $ <: actual user number of the current process
11. $>: valid user number of the current process
12. $ (: actual group user number of the current process
13. $): valid group user number of the current process
14. $ [: subscript of the first element of the array. The default value is 0.
15. $]: Perl version
16. $ ARGV: When "<>" is used to read a file, the current file name is saved.

4. Global Special array Variables

1. @ ARGV: Save the command line parameters.
2. @ INC: Save and find the directory of the Perl Program
3. @ _: In a subroutine, this array variable contains the parameters passed to the subroutine.
4.% INC: Hash List % INC contains all files contained in the do or require statement. The keyword is the file name and the value is the file path.
5.% ENV: contains the current environment variable

5. Global special file handle

1. ARGV: traverses the special file handle of 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

$-Number of printable lines on the current page, part of the Perl format system
$! Returns the error code or string based on the context content.
$ "List Separator
$ # Default digital output format when printing numbers
$ Perl interpreter process ID
$ % Current page number of the current output channel
$ & String matching the previous format
$ (Group ID of the current process
$) Valid group ID of the current process
$ * Setting 1 indicates processing the multiline format. It is replaced by the/s and/m modifiers.
$, Delimiter of the current output field
$. Current row number of the last Read File
$/Delimiter of the current input record. The default value is a new line.
$: Character setting. Subsequent strings are separated to fill continuous fields.
$; Delimiter used to simulate multi-dimensional arrays.
$? Returns the status of the last external command.
$ @ Error message returned by the Perl interpreter from the eval statement
$ [Index number of the first element in the array
$ Delimiter of the current output record
$] Sub-version number of the Perl interpreter
$ ^ Name of the top page output format of the current channel
$ ^ A variables used to save formatted data before printing
$ ^ D debug flag value
$ ^ E Operating System Extension error message in non-UNIX environment
$ ^ F maximum file bundle operator Value
$ ^ H check status of the syntax activated by the compiler
$ ^ I built-in control editor Value
$ ^ L form feed sent to the output channel
$ ^ M backup memory pool size
$ ^ O operating system name
$ ^ P specifies the internal variable of the current debugging Value
$ ^ R result of the last evaluation of the regular expression Block
$ ^ S current interpreter status
$ ^ T start from the new century, and the start time of the notebook is calculated in seconds.
$ ^ W current value of the warning Switch
$ ^ X Perl binary executable code name
$ _ Default input/output and format matching space
$ | Controls the buffer of the currently selected output file handle
$ ~ Name of the current report format
$ 'String before matching information in the previous format
$ 'String after matching information in the previous format
$ + The last parenthesis matching the previous regular expression search format
$ <Real id of the user currently executing the interpreter
$ Contains the matching result in parentheses corresponding to the previous Regular Expression
$ = Number of printable rows on the current page
$> Valid user ID of the current process
$0 contains the file name of the script being executed
$ ARGV current file name when reading from the default file handle
% ENV Environment Variable list
% INC list of files contained through do or require
% SIG signal list and Processing Method
@ _ List of parameters passed to the subroutine
@ ARGV: List of command line parameters passed to the script
@ INC: List of directories to be searched during module Import
$-[0] and $ + [0] represent the starting and ending positions of the currently matched Regular Expression in the matched string.