Perl - Topicalization and Special Variables

Topicalization and Special Variables - Perl module P210

Not all Perl variables are created as you run your code. Some useful information is provided in special variables before your code is even reached, and some of these special variables can be manipulated to affect the ongoing operation of your program. Perl even provides a facility that lets you leave parameters out of your source code, and it will assume a default current variable. This is known as topicalization.

This topic is presented on public courses Perl Programming, Perl bootcamp

Examples from our training material

allhosts	Special variable $/; reading whole file to scalar
cl2	Program that generates a warning
commline	Handling the command line via @ARGV
cv	rewrite of "dos2unix" in Perl
gop	Handling the command line via Getopt. Also Usage lines.
hodo	Filter looking for IP addresses of computer(s) with "tea" in name
infovars	English and short names for informational special variables
oddgrep	Using grep and map with $_
paws	Progress bar / progress reports
rqu	Use of awk-like options with Perl
sample	Filter - takes names and attempts to capitalise correctly
special1	Program using a variety of special variables
spout	Special variables to control output formatting of lists
ticker	Clock, using autoflush to update screen every second
top3	Further use of $_
topic1	Variable used many times - candidate for topicalisation
topic2	Topicalisation in use

Opentalk forum discussions related to this topic

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replace text in a large text file
Question regarding
Extracting some fields from a data File
Dialling codes for Ireland a quick Perl Script

Pictures

At the hotel at Dharhan International Airport
An on site course in early 2004

Background information

You may download this module as a sample of our material

Topics covered in this module

Regular variables in Perl.
Special variables.
Topicalization.
Special information variables and the English module.
Reading the command line in Perl.
Special variables that provide controls.
Output control variables.
Output buffering.
Input controls.
Special variables provided by Perl operations.
Error information.
Regular expression match information.
Other special variables you may come across.
Command line options.

Complete learning

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We have a technical library of over 600 books on the subjects on which we teach. These books are available for reference at our training centre. Also available is the Opentalk Forum for discussion of technical questions.