Minimal Perl: For UNIX and Linux People

Table of Contents

foreword
preface
acknowledgments
about this book
about the cover illustration
list of tables

Minimal Perl: for UNIX and Linux Users

1 Introducing Minimal Perl

A visit to Perlistan

Sometimes you need a professional guide

Perl can be simple

About Minimal Perl

What Minimal Perl isn't, What Minimal Perl is

Laziness is a virtue

A minimal dose of syntax

Terminating statements with semicolons

Writing one-line programs

Balancing simplicity and readability, Implementing simple filters

Summary

2 Perl essentials

Perl's invocation options

One-line programming: -e, Enabling warnings: -w, Processing input: -n, Processing input with automatic printing: -p, Processing line-endings: -l, Printing without newlines: printf, Changing the input record separator: -0digits

Using variables

Using special variables, Using the data variable: $_, Using the record-number variable: $., Employing user-defined variables

Loading modules -M

Writing simple scripts

Quoting techniques, True and False values, Handling switches: -s, Using warn and die, Using logical and, logical or, Programming with BEGINand END blocks, Loading modules with use

Additional special variables

Employing I/O variables, Exploiting formatting variables

Standard option clusters

Using aliases for common types of Perl commands

Constructing programs

Constructing an output-only one-liner, Constructing an input/output script

Summary

Directions for further study

3 Perl as a (better) grep command

A brief history of grep

Shortcomings of grep

Uncertain support for metacharacters, Lack of string escapes for control characters, Comparing capabilities of greppers and Perl

Working with the matching operator

The one-line Perl grepper

Understanding Perl's regex notation

Perl as a better fgrep

Displaying the match only, using $&

Displaying unmatched records (like grep -v), Validating data, Minimizing typing with shortcut metacharacters

Displaying filenames only (like grep -l)

Using matching modifiers

Ignoring case (like grep -i)

Perl as a better egrep

Working with cascading filters

Matching in context

Paragraph mode, File mode

Spanning lines with regexes

Matching across lines, Using lwp-request, Filtering lwp-request output

Additional examples

Log-file analysis, A scripted grepper, Fuzzy matching, Web scraping

Summary

Directions for further study

4 Perl as a (better) sed command

A brief history of sed

Shortcomings of sed

Performing substitutions

Performing line-specific substitutions: sed, Performing line-specific substitutions: Perl, Performing record-specific substitutions: Perl, Using backreferences and numbered variables in substitutions

Printing lines by number

Printing lines by number: sed, Printing lines by number: Perl, Printing records by number: Perl

Modifying templates

Converting special characters

Editing files

Editing with commands, Editing with scripts, Safeguarding in-place editing

Converting to lowercase or uppercase

Quieting spam

Substitutions with computed replacements

Converting miles to kilometers, Substitutions using function results

The sed to Perl translator

Summary

Directions for further study

5 Perl as a (better) awk command

A brief history of AWK

Comparing basic features of awk and Perl

Pattern-matching capabilities, Special variables, Perl's variable interpolation, Other advantages of Perl over AWK, Summary of differences in basic features

Processing fields

Accessing fields, Printing fields, Differences in syntax for print, Using custom field separators in Perl

Programming with Patterns and Actions

Combining pattern matching with field processing, Extracting data from tables, Accessing cell data using array indexing

Matching ranges of records

Operators for single- and multi-record ranges, Matching a range of dates, Matching multiple ranges

Using relational and arithmetic operators

Relational operators, Arithmetic operators

Using built-in functions

One-liners that use functions, The legend of nexpr, How the nexpr* programs work

Additional examples

Computing compound interest: compound_interest, Conditionally pluralizing nouns: compound_interest2, Analyzing log files: scan4oops

Using the AWK-to-Perl translator: a2p

Tips on using a2p

Summary

Directions for further study

6 Perl as a (better) find command

Introducing hybrid find / perl programs

File testing capabilities of find vs. Perl

Augmenting find with Perl

Finding files

Finding files by name matching, Finding files by pathname matching

Processing filename arguments

Defending against grep's messes, Recursive grepping, Perl as a generalized argument pre-processor

Using find | xargs vs. Perl alternatives

Using Perl for reliable timestamp sorting, Dealing with multi-word filenames

find as an argument pre-processor for Perl

A Unix-like, OS-portable find command

Making the most of find2perl, Helping non-Unix friends with find2perl

Summary

Directions for further study

Part 2 Minimal Perl: for UNIX and Linux Shell Programmers

7 Built-in functions

Understanding and managing evaluation context

Determinants and effects of evaluation context, Making use of evaluation context

Programming with functions that generate or process scalars

Using split, Using localtime, Using stat, Using chomp, Using rand

Programming with functions that process lists

Comparing Unix pipelines and Perl functions , Using sort, Using grep, Using join, Using map

Globbing for filenames

Tips on globbing

Managing files with functions

Handling multi-valued return codes

Parenthesizing function arguments

Controlling argument-gobbling functions

Summary

Directions for further study

8 Scripting techniques

Exploiting script-oriented functions

Defining defined, Exiting with exit, Shifting with shift

Pre-processing arguments

Accommodating non-filename arguments with implicit loops, Filtering arguments, Generating arguments

Executing code conditionally with if/else

Employing if/else vs. and/or, Mixing branching techniques: The cd_report script, Tips on using if/else

Wrangling strings with concatenation and repetition operators

Enhancing the most_recent_file script, Using concatenation and repetition operators together, Tips on using the concatenation operator

Interpolating command output into source code

Using the tput command, Grepping recursively: The rgrep script, Tips on using command interpolation

Executing OS commands using system

Generating reports, Tips on using system

Evaluating code using eval

Using a Perl shell: The psh script, Appreciating a multi-faceted Perl grepper: The preg script

Summary

Directions for further study

9 List variables

Using array variables

Initializing arrays with piecemeal assignments and push, Understanding advanced array indexing, Extracting fields in a friendlier fashion, Telling fortunes: The fcookie script, Tips on using arrays

Using hash variables

Initializing hashes, Understanding advanced hash indexing, Understanding the built-in %ENV hash, Printing hashes, Using %ENV in place of switches, Obtaining uniqueness with hashes, Employing a hash as a simple database: The user_lookup script, Counting word frequencies in web pages: The count_words script

Comparing list generators in the Shell and Perl

Filename generation/globbing, Command substitution/interpolation, Variable substitution/interpolation

Summary

Directions for further study

10 Looping facilities

Looping facilities in the Shell and Perl

Looping with while / until

Totaling numeric arguments, Reducing the size of an image, Printing key/value pairs from a hash using each, Understanding the implicit loop

Looping with do while / until

Prompting for input

Looping with foreach

Unlinking files: the rm_files script, Reading a line at a time, Printing a hash, Demystifying acronyms: The expand_acronyms script, Reducing image sizes: The compress_image2 script

Looping with for

Exploiting for's support for indexing: the raffle script

Using loop-control directives

Nesting loops within loops, Enabling loop-control directives in bottom-tested loops, Prompting for input, Enhancing loops with continue blocks: the confirmation script

The CPAN's select loop for Perl

Avoiding the re-invention of the "choose-from-a-menu" wheel, Monitoring user activity: the show_user script, Browsing man pages: the perlman script

Summary

Directions for further study

11 Subroutines and variable scoping

Compartmentalizing code with subroutines

Defining and using subroutines, Understanding use strict

Common problems with variables

Clobbering variables: The phone_home script, Masking variables: The 4letter_word script, Tips on avoiding problems with variables

Controlling variable scoping

Declaring variables with my , Declaring variables with our , Declaring variables with local, Introducing the Variable Scoping Guidelines

Variable Scoping Guidelines for complex programs

Enable use strict, Declare user-defined variables and define their scopes, Pass data to subroutines using arguments, Localize temporary changes to built-in variables with local, Employ user-defined loop variables ,Applying the Guidelines: the phone_home2 script

Reusing a subroutine

Summary

Directions for further study

12 Modules and the CPAN

Creating modules

Using the Simple Module Template, Creating a module: Center.pm, Testing a new module

Managing modules

Identifying the modules that you want, Determining whether you have a certain module, Installing modules from the CPAN

Using modules

Business::UPS-the ups_shipping_price script, LWP::Simple-the check_links script, Shell::POSIX::Select-the menu_ls script, File::Find-the check_symlinks script, CGI-the survey.cgi script, Tips on using Object-Oriented modules

Summary

Directions for further study

epilogue 426
appendix A: Perl special variables cheatsheet 427
appendix B: Guidelines for parenthesizing code 430
glossary 432
index 443