Perl's special variables : Special Variables « Language Basics « Perl

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Perl » Language Basics » Special Variables 
Perl's special variables
   

VARIABLE    DEFAULT VALUE    DESCRIPTION

$_          N/A              The default input and pattern-searching space.

$digit      N/A              Contains the subpattern from a successful parentheses pattern match.

$&          N/A              The string from the last successful pattern match.

$æ          N/A              The preceding string to the last successful pattern match.

$'          N/A              The string following the last successful pattern match.

$+          N/A              The last bracket matched from the last search pattern.

$*          0                Controls internal string multiline pattern matching.

$.          N/A              The current input line number of last filehandle read.

$/          \n               The input record separator.

$|          0                If set to nonzero, forces a flush of the currently selected stream after every write.

$,          N/A              The output field separator for the print command.

$"          Space            The separator that joins elements of arrays interpolated in strings.

$\          N/A              The output record separator for the print command.

$;          \034             The subscript separator for multidimensional array emulation. 

$#          N/A              The output format for printed numbers.

$%          N/A              The page number of the currently selected output stream.

$=          60               The page length of the currently selected output stream.

$–          N/A              The number of lines left on the current page.

$˜          filehandle       The name of the current top of page format for the currently selected output stream.

$:          \n-              The characters used to fill a continuation field.

$˜L         \f               The default form-feed character.

$?          N/A              The status value returned from the last system, pipe close, or back tick command.

$!          N/A              Contains the current value of errno.

$@          N/A              The Perl syntax error from the last eval statement.

$$          N/A              The process ID (PID) of the current running Perl script.

$<          N/A              The real user ID (UID) of the current running process.

$>          N/A              The effective UID of the current running process.

$(          N/A              The real group ID (GID) of the current running process.

$)          N/A              The effective GID of the current running process.

$0          N/A              The name of the file of the Perl script.

$[          0                The index of the first element of an array. 

$]          N/A              The string printed out when Perl is run with the -v command line option.

$˜A         N/A              The accumulator for form line and write operations.

$˜D         N/A              The current value of the debugging flags.

$˜F         2                The maximum number of system file descriptors.

$˜I         N/A              Contains the current value of the in-place editing flag (-i).

$˜P         N/A              Internal debugging flag.

$˜T         N/A              The time in which the script began running. 

$˜W         N/A              The current value of the warning switch.

$˜X         N/A              The name of the Perl binary that was executed.

$ARGV       N/A              The name of the current file when reading from <>.

   
    
    
  
Related examples in the same category
1. Special Literals
2. Splitting up $_
3. Splitting up $_ and creating an unnamed list
4. The list separator is a comma
5. The list separator is the empty string
6. Passing Arguments at the Command Line
7. Special Hashes: The %ENV Hash
8. The %SIG hash sets signal handlers for signals.
9. A program that changes the value of $/.
10. A program that uses the $" (dollar and quotation) variable.
11. A program that uses the $(dollar), variable.
12. A program that uses the $< variable.
13. A program that uses the $\(dollar and slash) variable.
14. A simple program that assigns to $_ using .
15. A simple version of the cat command using $_.
16. ARGV and the Null Filehandle
17. ARGV in Perl represents the command-line arguments.
18. Aliases and Values
19. Alternative names for Perl system variables.
20. Assign elements in @_ to scalar
21. Assign string array to @ARGV by using qw
22. Assign value to @_
23. Build the ARGV array with qw function
24. @_ has runtime scope.
25. A more expanded version for showing how to use the $_
26. Built-in variables: $_
27. Call-by-Reference and the @_ Array
28. Capturing fatal errors
29. Catching the sigINT signal
30. Code the $_ specifically
31. Compare value entered with number with underscore
32. Error message is stored in $!
33. Extracts information from the $] variable.
34. $! is the error number
35. $! stores the error message
36. $" is the separator
37. $# is the default format
38. $(dollar), is the separator
39. $MATCH = $&
40. $SIG{__DIE__}
41. $SIG{__WARN__} = 'IGNORE';
42. $SIG{__WARN__} = sub {die "Warning: $_[0]"};
43. $\ is 'END_OF_OUTPUT'
44. $^ is the format header
45. $^O stores the name of the operating system
46. $^S: is inside eval
47. $^W: Check the '-w switch'
48. $^X: get the Perl execuatable file name
49. $_ for print function
50. $_ stores the user input
51. $~ is the format
52. %INC values
53. File-searching program using $ARGV.
54. Get Computer Name key in the %ENV
55. Get local time from $^T
56. If $_contains needle, the string is printed.
57. Integer signal
58. Lines Remaining on the Page: $-
59. List all command line argument
60. Local builtin var
61. Locate all numbers less than 6
62. Manipuate @_ and return @_
63. Mannually change the $1 variable
64. Match: $&
65. Perl 5 Built-In Variables
66. Perl's modules reside in the directories named in the @INC array, or subdirectories
67. Perl's special arrays
68. Postmatch $'
69. Prematch: $`
70. Print all command line argument
71. Print the default variable's ($_) value
72. Quick Sum
73. Read and set environment variables?
74. Read lines from supplied filenames
75. Reference element in @_
76. Resetting array base
77. Retrieving the Entire Pattern: $&
78. Saving in the $& special scalar
79. Set the $/ and chomp
80. Special Variables
81. System variables that control how write sends output to a file
82. Test of open and die with $!.
83. The $_ Scalar Variable
84. The @* field
85. The @ISA Array and Calling Methods
86. The Argument Vector @ARGV
87. The Pattern-Matching Operator and $_
88. The Substitution Operator and $_
89. The code executes a line of code you type as long as that line doesn't start with a #
90. The environment associative array: Associative arrays %ENV holds your system's environment variables.
91. The following functions and operators work with the $_ variable by default:
92. The shift operator returns an undefined value if the array has no more elements.
93. To list all .pm files by using the @INC array
94. Use while loop to display all entries in ENV
95. Using $, to set the separator for print command
96. Using $_ (dollar underscore)
97. Using $_ as the array index
98. Using $_ variable with while statement
99. Using %SIG to define our own signal handlers
100. Using @_ directly
101. Using __LINE__ to output line number
102. Using eof and <> together.
103. Using the $. variable.
104. Using the $;(dollar and semicolon) variable.
105. Using the @_ to reference the parameter
106. Using the Default Variable $_
107. Using the diamond operator with @ARGV
108. Using the if statement to check the command line parameters
109. Using the special Perl variable $! in the message passed to die.
110. Using tr to convert all file names passed in to uppercase
111. Verify the total number of the command line parameter
112. Working with $_ usually makes programming much easier, but more confusing to the uninitiated
113. You display the current line of execution in a Perl script by referring to it with the __LINE__ token.
114. You display the name of the current Perl package with __PACKAGE__.
115. You display the name of the current file with the __FILE__ token
116. foreach (@_)
117. foreach loop and $_
118. or die $!
119. or die $^E;
120. print "Hello, $ENV{USER}!\n";
121. print $INC{'English.pm'};
122. print $]; (Perl version number)
123. print out all pm library location
124. prints out each element of @ARGV separately
125. shift: defaults to shifting @ARGV
126. time - $^T
127. undef $/;
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