Literal Tokens in Perl in Objective-C

Creation PDF 417 in Objective-C Literal Tokens in Perl

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Note that Perl uses a combination of special characters and names to refer to the individual variables To use the long (named) variables, you must include the English module by placing

use English;

at the top of your program By including this module, you arrange that the longer names will be aliased to the shortened versions Although there is no standard for using either format, because the shortened versions are the default, you will see them used more widely See Web Appendix A for a listing of the variables and their English module equivalents The named examples are given here for reference Some of the variables also have equivalent methods that are supported by the IO::* range of modules The format of these method calls is method HANDLE EXPR (you can also use HANDLE->method(EXPR)), where HANDLE is the filehandle you want the change to apply to, and EXPR is the value to be supplied to the method

_ (underscore) The underscore represents the special filehandle used to cache information from the last successful stat, lstat, or file test operator $0 $PROGRAM_NAME

$1$xx The numbered variables $1, $2, and so on are the variables used to hold the contents of group matches both inside and outside of regular expressions

The $_ and $ARG variables represent the default input and pattern searching spaces For many functions and operations, if no specific variable is specified, the default input space will be used For example,

$_ = "Hello World\n"; print;

would print the Hello World message The same variable is also used in regular expression substitution and pattern matches We ll look at this more closely in 7

Perl will automatically use the default space in the following situations even if you do not specify it: I Unary functions, such as ord and int I All file tests except -t, which defaults to STDIN I Most of the functions that support lists as arguments (see Appendix A) I The pattern matching operations, m//, s///, and tr///, when used without an =~ operator I The default iterator variable in a for or foreach loop, if no other variable is supplied I The implicit operator in map and grep functions I The default place to store an input record when reading from a filehandle

$* Set to 1 to do multiline pattern matching within a string The default value is 0 The use of this variable has been superseded by the /s and /m modifiers to regular expressions

Contains a list of all the offsets of the last successful submatches from the last regular expression Note that this contains the offset to the first character following the match, not the location of the match itself This is the equivalent of the value returned by the pos function The first index, $+[0] is offset to the end of the entire match Therefore, $+[1] is the location where $1 ends, $+[2], where $2 ends

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Contains a list of all the offsets to the beginning of the last successful submatches from the last regular expression The first index, $-[0], is offset to the start of the entire match Therefore, $-[1] is equal to $1, $-[2] is equal to $2, and so on

The current input line number of the last file from which you read This can be either the keyboard or an external file or other filehandle (such as a network socket) Note that it s based not on what the real lines are, but more what the number of the last record was according to the setting of the $/ variable

The current input record separator This is newline by default, but it can be set to any string to enable you to read in delimited text files that use one or more special characters to separate the records You can also undefine the variable, which will allow you to read in an entire file, although this is best done using local within a block:

{ local $/; $file = <FILE>; }