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Perl Cookbook

Tips and Tricks for Perl Programmers

By Tom Christiansen, Nathan Torkington

Publisher: O'Reilly Media

Final Release Date: August 1998

Pages: 800

The Perl Cookbook is a comprehensive collection of problems, solutions, and practical examples for anyone programming in Perl. Topics range from beginner questions to techniques that even the most experienced of Perl programmers will learn from. More than just a collection of tips and tricks, the Perl Cookbook is the long-awaited companion volume to Programming Perl, filled with previously unpublished Perl arcana.The Perl Cookbook contains thousands upon thousands of examples ranging from brief one-liners to complete applications. Covered topic areas spread across nearly four hundred separate "recipes," including:

Manipulation of strings, numbers, dates, arrays, and hashes
Reading, writing, and updating text and binary files
Pattern matching and text substitutions
Subroutines, libraries, and modules
References, data structures, objects, and classes
Signals and exceptions
Accessing text, hashes, and SQL databases
Screen addressing, menus, and graphical applications
Managing other processes
Writing secure scripts
Client-server programming
Internet applications programming with mail, news, ftp, and telnet

These recipes were rigorously reviewed by scores of the best minds inside and outside Perl, foremost of which was Larry Wall, the creator of Perl himself.The Perl Cookbook is written by Tom Christiansen, Perl evangelist and coauthor of the bestselling Programming Perl and Learning Perl; and Nathan Torkington, Perl trainer and co-maintainer of the Perl Frequently Asked Questions list.

Chapter 1 Strings
1. Introduction
2. Accessing Substrings
3. Establishing a Default Value
4. Exchanging Values Without Using Temporary Variables
5. Converting Between ASCII Characters and Values
6. Processing a String One Character at a Time
7. Reversing a String by Word or Character
8. Expanding and Compressing Tabs
9. Expanding Variables in User Input
10. Controlling Case
11. Interpolating Functions and Expressions Within Strings
12. Indenting Here Documents
13. Reformatting Paragraphs
14. Escaping Characters
15. Trimming Blanks from the Ends of a String
16. Parsing Comma-Separated Data
17. Soundex Matching
18. Program: fixstyle
19. Program: psgrep
Chapter 2 Numbers
1. Introduction
2. Checking Whether a String Is a Valid Number
3. Comparing Floating-Point Numbers
4. Rounding Floating-Point Numbers
5. Converting Between Binary and Decimal
6. Operating on a Series of Integers
7. Working with Roman Numerals
8. Generating Random Numbers
9. Generating Different Random Numbers
10. Making Numbers Even More Random
11. Generating Biased Random Numbers
12. Doing Trigonometry in Degrees, not Radians
13. Calculating More Trigonometric Functions
14. Taking Logarithms
15. Multiplying Matrices
16. Using Complex Numbers
17. Converting Between Octal and Hexadecimal
18. Putting Commas in Numbers
19. Printing Correct Plurals
20. Program: Calculating Prime Factors
Chapter 3 Dates and Times
1. Introduction
2. Finding Today’s Date
3. Converting DMYHMS to Epoch Seconds
4. Converting Epoch Seconds to DMYHMS
5. Adding to or Subtracting from a Date
6. Difference of Two Dates
7. Day in a Week/Month/Year or Week Number
8. Parsing Dates and Times from Strings
9. Printing a Date
10. High-Resolution Timers
11. Short Sleeps
12. Program: hopdelta
Chapter 4 Arrays
1. Introduction
2. Specifying a List In Your Program
3. Printing a List with Commas
4. Changing Array Size
5. Doing Something with Every Element in a List
6. Iterating Over an Array by Reference
7. Extracting Unique Elements from a List
8. Finding Elements in One Array but Not Another
9. Computing Union, Intersection, or Difference of Unique Lists
10. Appending One Array to Another
11. Reversing an Array
12. Processing Multiple Elements of an Array
13. Finding the First List Element That Passes a Test
14. Finding All Elements in an Array Matching Certain Criteria
15. Sorting an Array Numerically
16. Sorting a List by Computable Field
17. Implementing a Circular List
18. Randomizing an Array
19. Program: words
20. Program: permute
Chapter 5 Hashes
1. Introduction
2. Adding an Element to a Hash
3. Testing for the Presence of a Key in a Hash
4. Deleting from a Hash
5. Traversing a Hash
6. Printing a Hash
7. Retrieving from a Hash in Insertion Order
8. Hashes with Multiple Values Per Key
9. Inverting a Hash
10. Sorting a Hash
11. Merging Hashes
12. Finding Common or Different Keys in Two Hashes
13. Hashing References
14. Presizing a Hash
15. Finding the Most Common Anything
16. Representing Relationships Between Data
17. Program: dutree
Chapter 6 Pattern Matching
1. Introduction
2. Copying and Substituting Simultaneously
3. Matching Letters
4. Matching Words
5. Commenting Regular Expressions
6. Finding the Nth Occurrence of a Match
7. Matching Multiple Lines
8. Reading Records with a Pattern Separator
9. Extracting a Range of Lines
10. Matching Shell Globs as Regular Expressions
11. Speeding Up Interpolated Matches
12. Testing for a Valid Pattern
13. Honoring Locale Settings in Regular Expressions
14. Approximate Matching
15. Matching from Where the Last Pattern Left Off
16. Greedy and Non-Greedy Matches
17. Detecting Duplicate Words
18. Expressing AND, OR, and NOT in a Single Pattern
19. Matching Multiple-Byte Characters
20. Matching a Valid Mail Address
21. Matching Abbreviations
22. Program: urlify
23. Program: tcgrep
24. Regular Expression Grabbag
Chapter 7 File Access
1. Introduction
2. Opening a File
3. Opening Files with Unusual Filenames
4. Expanding Tildes in Filenames
5. Making Perl Report Filenames in Errors
6. Creating Temporary Files
7. Storing Files Inside Your Program Text
8. Writing a Filter
9. Modifying a File in Place with Temporary File
10. Modifying a File in Place with -i Switch
11. Modifying a File in Place Without a Temporary File
12. Locking a File
13. Flushing Output
14. Reading from Many Filehandles Without Blocking
15. Doing Non-Blocking I/O
16. Determining the Number of Bytes to Read
17. Storing Filehandles in Variables
18. Caching Open Output Filehandles
19. Printing to Many Filehandles Simultaneously
20. Opening and Closing File Descriptors by Number
21. Copying Filehandles
22. Program: netlock
23. Program: lockarea
Chapter 8 File Contents
1. Introduction
2. Reading Lines with Continuation Characters
3. Counting Lines (or Paragraphs or Records) in a File
4. Processing Every Word in a File
5. Reading a File Backwards by Line or Paragraph
6. Trailing a Growing File
7. Picking a Random Line from a File
8. Randomizing All Lines
9. Reading a Particular Line in a File
10. Processing Variable-Length Text Fields
11. Removing the Last Line of a File
12. Processing Binary Files
13. Using Random-Access I/O
14. Updating a Random-Access File
15. Reading a String from a Binary File
16. Reading Fixed-Length Records
17. Reading Configuration Files
18. Testing a File for Trustworthiness
19. Program: tailwtmp
20. Program: tctee
21. Program: laston
Chapter 9 Directories
1. Introduction
2. Getting and Setting Timestamps
3. Deleting a File
4. Copying or Moving a File
5. Recognizing Two Names for the Same File
6. Processing All Files in a Directory
7. Globbing, or Getting a List of Filenames Matching a Pattern
8. Processing All Files in a Directory Recursively
9. Removing a Directory and Its Contents
10. Renaming Files
11. Splitting a Filename into Its Component Parts
12. Program: symirror
13. Program: lst
Chapter 10 Subroutines
1. Introduction
2. Accessing Subroutine Arguments
3. Making Variables Private to a Function
4. Creating Persistent Private Variables
5. Determining Current Function Name
6. Passing Arrays and Hashes by Reference
7. Detecting Return Context
8. Passing by Named Parameter
9. Skipping Selected Return Values
10. Returning More Than One Array or Hash
11. Returning Failure
12. Prototyping Functions
13. Handling Exceptions
14. Saving Global Values
15. Redefining a Function
16. Trapping Undefined Function Calls with AUTOLOAD
17. Nesting Subroutines
18. Program: Sorting Your Mail
Chapter 11 References and Records
1. Introduction
2. Taking References to Arrays
3. Making Hashes of Arrays
4. Taking References to Hashes
5. Taking References to Functions
6. Taking References to Scalars
7. Creating Arrays of Scalar References
8. Using Closures Instead of Objects
9. Creating References to Methods
10. Constructing Records
11. Reading and Writing Hash Records to Text Files
12. Printing Data Structures
13. Copying Data Structures
14. Storing Data Structures to Disk
15. Transparently Persistent Data Structures
16. Program: Binary Trees
Chapter 12 Packages, Libraries, and Modules
1. Introduction
2. Defining a Module’s Interface
3. Trapping Errors in require or use
4. Delaying use Until Run Time
5. Making Variables Private to a Module
6. Determining the Caller’s Package
7. Automating Module Clean-Up
8. Keeping Your Own Module Directory
9. Preparing a Module for Distribution
10. Speeding Module Loading with SelfLoader
11. Speeding Up Module Loading with Autoloader
12. Overriding Built-In Functions
13. Reporting Errors and Warnings Like Built-Ins
14. Referring to Packages Indirectly
15. Using h2ph to Translate C #include Files
16. Using h2xs to Make a Module with C Code
17. Documenting Your Module with Pod
18. Building and Installing a CPAN Module
19. Example: Module Template
20. Program: Finding Versions and Descriptions of Installed Modules
Chapter 13 Classes, Objects, and Ties
1. Introduction
2. Constructing an Object
3. Destroying an Object
4. Managing Instance Data
5. Managing Class Data
6. Using Classes as Structs
7. Cloning Objects
8. Calling Methods Indirectly
9. Determining Subclass Membership
10. Writing an Inheritable Class
11. Accessing Overridden Methods
12. Generating Attribute Methods Using AUTOLOAD
13. Solving the Data Inheritance Problem
14. Coping with Circular Data Structures
15. Overloading Operators
16. Creating Magic Variables with tie
Chapter 14 Database Access
1. Introduction
2. Making and Using a DBM File
3. Emptying a DBM File
4. Converting Between DBM Files
5. Merging DBM Files
6. Locking DBM Files
7. Sorting Large DBM Files
8. Treating a Text File as a Database Array
9. Storing Complex Data in a DBM File
10. Persistent Data
11. Executing an SQL Command Using DBI and DBD
12. Program: ggh—Grep Netscape Global History
Chapter 15 User Interfaces
1. Introduction
2. Parsing Program Arguments
3. Testing Whether a Program Is Running Interactively
4. Clearing the Screen
5. Determining Terminal or Window Size
6. Changing Text Color
7. Reading from the Keyboard
8. Ringing the Terminal Bell
9. Using POSIX termios
10. Checking for Waiting Input
11. Reading Passwords
12. Editing Input
13. Managing the Screen
14. Controlling Another Program with Expect
15. Creating Menus with Tk
16. Creating Dialog Boxes with Tk
17. Responding to Tk Resize Events
18. Removing the DOS Shell Window with Windows Perl/Tk
19. Program: Small termcap program
20. Program: tkshufflepod
Chapter 16 Process Management and Communication
1. Introduction
2. Gathering Output from a Program
3. Running Another Program
4. Replacing the Current Program with a Different One
5. Reading or Writing to Another Program
6. Filtering Your Own Output
7. Preprocessing Input
8. Reading STDERR from a Program
9. Controlling Input and Output of Another Program
10. Controlling the Input, Output, and Error of Another Program
11. Communicating Between Related Processes
12. Making a Process Look Like a File with Named Pipes
13. Sharing Variables in Different Processes
14. Listing Available Signals
15. Sending a Signal
16. Installing a Signal Handler
17. Temporarily Overriding a Signal Handler
18. Writing a Signal Handler
19. Catching Ctrl-C
20. Avoiding Zombie Processes
21. Blocking Signals
22. Timing Out an Operation
23. Program: sigrand
Chapter 17 Sockets
1. Introduction
2. Writing a TCP Client
3. Writing a TCP Server
4. Communicating over TCP
5. Setting Up a UDP Client
6. Setting Up a UDP Server
7. Using UNIX Domain Sockets
8. Identifying the Other End of a Socket
9. Finding Your Own Name and Address
10. Closing a Socket After Forking
11. Writing Bidirectional Clients
12. Forking Servers
13. Pre-Forking Servers
14. Non-Forking Servers
15. Writing a Multi-Homed Server
16. Making a Daemon Server
17. Restarting a Server on Demand
18. Program: backsniff
19. Program: fwdport
Chapter 18 Internet Services
1. Introduction
2. Simple DNS Lookups
3. Being an FTP Client
4. Sending Mail
5. Reading and Posting Usenet News Messages
6. Reading Mail with POP3
7. Simulating Telnet from a Program
8. Pinging a Machine
9. Using Whois to Retrieve Information from the InterNIC
10. Program: expn and vrfy
Chapter 19 CGI Programming
1. Introduction
2. Writing a CGI Script
3. Redirecting Error Messages
4. Fixing a 500 Server Error
5. Writing a Safe CGI Program
6. Making CGI Scripts Efficient
7. Executing Commands Without Shell Escapes
8. Formatting Lists and Tables with HTML Shortcuts
9. Redirecting to a Different Location
10. Debugging the Raw HTTP Exchange
11. Managing Cookies
12. Creating Sticky Widgets
13. Writing a Multiscreen CGI Script
14. Saving a Form to a File or Mail Pipe
15. Program: chemiserie
Chapter 20 Web Automation
1. Introduction
2. Fetching a URL from a Perl Script
3. Automating Form Submission
4. Extracting URLs
5. Converting ASCII to HTML
6. Converting HTML to ASCII
7. Extracting or Removing HTML Tags
8. Finding Stale Links
9. Finding Fresh Links
10. Creating HTML Templates
11. Mirroring Web Pages
12. Creating a Robot
13. Parsing a Web Server Log File
14. Processing Server Logs
15. Program: htmlsub
16. Program: hrefsub

Colophon

Title:

Perl Cookbook

By:

Tom Christiansen, Nathan Torkington

Publisher:

O'Reilly Media

Formats:

Print
Safari Books Online

Print:

August 1998

Pages:

800

Print ISBN:

978-1-56592-243-3

| ISBN 10:

1-56592-243-3

Tom Christiansen

Tom Christiansen is a freelance consultant specializing in Perl training and writing. After working for several years for TSR Hobbies (of Dungeons and Dragons fame), he set off for college where he spent a year in Spain and five in America, dabbling in music, linguistics, programming, and some half-dozen different spoken languages. Tom finally escaped UW-Madison with B.A.s in Spanish and computer science and an M.S. in computer science. He then spent five years at Convex as a jack-of-all-trades working on everything from system administration to utility and kernel development, with customer support and training thrown in for good measure. Tom also served two terms on the USENIX Association Board of directors. With over fifteen years' experience in UNIX system administration and programming, Tom presents seminars internationally. Living in the foothills above Boulder, Colorado, surrounded by mule deer, skunks, and the occasional mountain lion and black bear, Tom takes summers off for hiking, hacking, birding, music making, and gaming.

View Tom Christiansen's full profile page.
Nathan Torkington

Nathan Torkington is a banjo player, father, and husband. His crimes in the computing community include: coauthor of the Perl Cookbook, editor for O'Reilly and Associates, content coordinator for the Open Source Convention and Perl Conference, and project manager for perl6.

View Nathan Torkington's full profile page.

Colophon

Our look is the result of reader comments, our own experimentation, and feedback from distribution channels. Distinctive covers complement our distinctive approach to technical topics, breathing personality and life into potentially dry subjects. The animal featured on the cover of Perl Cookbook is a bighorn sheep. Bighorn sheep (Ovis canadensis) are wild sheep noted, not surprisingly, for their large, curved horns. Male bighorns grow to approximately 5 feet long and 40 inches tall to the shoulder and weigh up to 350 pounds. Their horns measure up to 18 inches in circumference and 4 feet long and can weigh up to 30 pounds. Despite their bulk, bighorns are adept at negotiating mountainous terrains. With their sharp, cloven hooves they can walk on ledges as thin as two inches. They have excellent eyesight that enables them to locate footholds and to accurately judge distances between ledges. They can jump as far as 20 feet from ledge to ledge.Competition for ewes is intense and often leads to fierce battles that can continue for a full day. During the battle two rams race at each other at speeds of up to 20 miles an hour, clashing their horns together. The skull of the bighorn sheep is double-layered to provide protection from these blows. Horn size is a significant factor in determining rank, and rams will only fight other rams with an equivalently sized horn. Mature males usually stay apart from the females and young. In these "bachelor flocks" the lower-ranking males often play the part of ewes and behave in a submissive manner toward the dominant males. The dominant male, in turn, behaves like a courting ram and mounts the lower-ranking male. This behavior is believed to enable the rams to live together without rank disputes that might otherwise drive the lower-ranking males out of the flock.Bighorns can be found in the Rocky Mountains from Canada to Colorado and in the desert from California to west Texas and Mexico. They are threatened with extinction as a result of disease, habitat reduction, and hunting. Clairemarie Fisher O'Leary was the production editor and project manager for this book. Steven Kleinedler copyedited, Kristin Barendsen and Kristine Simmons proofread, and Jane Ellin and Sheryl Avruch provided quality control reviews. Trisha Manoni, Sebastian Banker, and Kimo Carter provided production assistance. Seth Maislin wrote the index. The illustrations were created in Macromedia Freehand 7.0 by Robert Romano. Edie Freedman designed the cover, using a 19th-century engraving from the Dover Pictorial Archive. The cover layout was produced with Quark XPress 3.32 using the ITC Garamond font. The inside layout was designed by Edie Freedman and modified by Nancy Priest and implemented in FrameMaker by Mike Sierra. The text and heading fonts are ITC Garamond Light and Garamond Book. This colophon was written by Clairemarie Fisher O'Leary.

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Customer Reviews

REVIEW SNAPSHOT®

by PowerReviews

oreillyPerl Cookbook

4.4

(based on 12 reviews)

Reviewed by 12 customers

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6/22/2010

5.0

One of the best Perl books

By fdegir

from Stockholm

About Me Designer, Developer

Pros

Accurate
Concise
Easy to understand
Helpful examples
Well-written

Cons

Best Uses

Expert
Intermediate

Comments about oreilly Perl Cookbook:

This is one of the best Perl books I've ever had. It takes the problem, explains the solution and gives hints about the code itself.

Must have book.

6/10/2003

5.0

Perl Cookbook Review

By Wortwart

from Undisclosed

Comments about oreilly Perl Cookbook:

You work with Perl? You need this book - almost daily. It gives you well written explanations of code snippets for your everyday work. Indispensable!

2/26/2003

4.0

Perl Cookbook Review

By Al Rizo-Patron

from Undisclosed

Comments about oreilly Perl Cookbook:

A clarification to my previous comment: I said tctee.pl does not work for binary files. That is true only for Windows, not Unix. To make it work for Windows, it needs to use the binmode() function on the filehandles. Unix ignores binmode(), and then again, it already has 'tee'. Still, tctee example given can be *very* slow in Windows on binary files because any character picked as a record delimiter could occur literally millions of times. Therefore, the I/O is better done with sysread() and syswrite() with a reasonably sized block size, or something like $blksize = (stat $fh)[11] || 131072;

2/24/2003

(1 of 1 customers found this review helpful)

4.0

Perl Cookbook Review

By Al Rizo-Patron

from Undisclosed

Comments about oreilly Perl Cookbook:

Excellent, practical complement to the Camel book.

One comment though: In example 8.19 Program: tctee (pages 304-306) the author states this "tee" replacement is one of the many venerable Perl programs written nearly a decade ago that still runs perfectly well... But if it ain't broke..."

Unfortunately, tctee.pl is not a replacement for tee. While tctee.pl handles text files OK, it does not work for binary files, whereas "tee" does.

It's left as homework for the reader to work a more general solution that does subsume tee.

In spite of this "nit," this is definitely a book to have handy when you want to solve some practical problem in short order.

2/8/2002

4.0

Perl Cookbook Review

By Julio

from Undisclosed

Comments about oreilly Perl Cookbook:

Are you hungry for Perl then the CookBook provides the right menu of recipies.

Small samples of perl programs all over the book to solve particular problems.

I can always learn from any program example (you can get good Ideas to solve your own problems or maybe if you get lucky your problem solution is on the book) the good ones and the bad ones there is also a lot of information. If you are a novice or advance user you will be able to benefit from this book alike.

If you can only afford two perl books go for Programming Perl (Cammel Book ) and this one!.

4/1/2001

5.0

Perl Cookbook Review

By Pete Nelson

from Undisclosed

Comments about oreilly Perl Cookbook:

The Perl Cookbook is the most definative, useful programming book I have ever seen. Very well organized, a quick glance through the table of contents will usually point you to the answer to just about any How do I ... ? question.

I think the quality and organization of this book is a stunning example of how a good programming reference should be written. I only wish there was something comperable for Java!

If you use perl at all, this book belongs open on your desk! It will save you hours of digging!

3/19/2001

(1 of 1 customers found this review helpful)

5.0

Perl Cookbook Review

By John Powell

from Undisclosed

Comments about oreilly Perl Cookbook:

This is the book that takes you over the (Camel's) hump from "Perl student" to "Perl user". I had read the Camel book, thought I had some clue, but locked up when it came to actually doing something useful. The well documented recipes in this book got me past roadblocks and into the realm of productivity. Without it, I would probably still be wallowing in Excel and a text editor to parse log files.

I HIGHLY recommend this book to other Perl newbies trying to bridge the gap between knowing the basics and actually doing something with it. This book ROCKS!

3/2/2001

4.0

Perl Cookbook Review

By Ismo Kallioniemi

from Undisclosed

Comments about oreilly Perl Cookbook:

Quite excellent book. Having read the 'Lama' and 'Camel' this is actually the book that gets it all together. If you learn from examples of code, this is definetally the book you should have.

2/16/2001

4.0

Perl Cookbook Review

By Michael Turley

from Undisclosed

Comments about oreilly Perl Cookbook:

Re: Previous comment

Sorry, just remembered that you can 'use lib "/path/to/myperlmods/"' to include Perl modules not installed on your perl installation. Should have read chapter 12 before posting last comment!

2/16/2001

4.0

Perl Cookbook Review

By Michael Turley

from Undisclosed

Comments about oreilly Perl Cookbook:

Excellent practical book - the only problem I had is that alot of the examples seem to be based on modules which you may not have the rights to install or may make an application less portable. The book is still first-rate though.

Displaying reviews 1-10

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Chapter 1 Strings

Introduction

Accessing Substrings

Establishing a Default Value

Exchanging Values Without Using Temporary Variables

Converting Between ASCII Characters and Values

Processing a String One Character at a Time

Reversing a String by Word or Character

Expanding and Compressing Tabs

Expanding Variables in User Input

Controlling Case

Interpolating Functions and Expressions Within Strings

Indenting Here Documents

Reformatting Paragraphs

Escaping Characters

Trimming Blanks from the Ends of a String

Parsing Comma-Separated Data

Soundex Matching

Program: fixstyle

Program: psgrep

Chapter 2 Numbers

Introduction

Checking Whether a String Is a Valid Number

Comparing Floating-Point Numbers

Rounding Floating-Point Numbers

Converting Between Binary and Decimal

Operating on a Series of Integers

Working with Roman Numerals

Generating Random Numbers

Generating Different Random Numbers

Making Numbers Even More Random

Generating Biased Random Numbers

Doing Trigonometry in Degrees, not Radians

Calculating More Trigonometric Functions

Taking Logarithms

Multiplying Matrices

Using Complex Numbers

Converting Between Octal and Hexadecimal

Putting Commas in Numbers

Printing Correct Plurals

Program: Calculating Prime Factors

Chapter 3 Dates and Times

Introduction

Finding Today’s Date

Converting DMYHMS to Epoch Seconds

Converting Epoch Seconds to DMYHMS

Adding to or Subtracting from a Date

Difference of Two Dates

Day in a Week/Month/Year or Week Number

Parsing Dates and Times from Strings

Printing a Date

High-Resolution Timers

Short Sleeps

Program: hopdelta

Chapter 4 Arrays

Introduction

Specifying a List In Your Program

Printing a List with Commas

Changing Array Size

Doing Something with Every Element in a List

Iterating Over an Array by Reference

Extracting Unique Elements from a List

Finding Elements in One Array but Not Another

Computing Union, Intersection, or Difference of Unique Lists

Appending One Array to Another

Reversing an Array

Processing Multiple Elements of an Array

Finding the First List Element That Passes a Test

Finding All Elements in an Array Matching Certain Criteria

Sorting an Array Numerically

Sorting a List by Computable Field

Implementing a Circular List

Randomizing an Array

Program: words

Program: permute

Chapter 5 Hashes

Introduction

Adding an Element to a Hash

Testing for the Presence of a Key in a Hash

Deleting from a Hash