How To See If A Specific Record Exists - Perl

Welcome to the ninth installment in our look at working with hashes and lists in Perl. In our previous article we learned how to add records to a hash, replace them, and delete the values inside of them. In this article we will learn how to check whether records reside within our hashes, write the data within a hash to a file, and create multidimensional lists.

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By: James Payne

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May 12, 2008

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Checking whether a hash contains any data whatsoever is good, but what if we need something a little more specific? For that we could use our good old buddy the exist() function, which, as the name implies, checks to see if a specific key exists. Here it is in action, checking whether the “Champ” is in our hash:

#!/usr/bin/perl

%Wrestlers=(Chump => ' Chavo Guerrero ', OldSkool=> ' Big John Stud ',

Boof=> ' Brutus Beefcake ');

unless(exists($Wrestlers{Champ}))

{ print "Where is the champ?"}

Since the “Champ” key does not exist, the print function is triggered, resulting in:

Where is the champ?

And of course, just as before, we can use if to check if the value is in the hash and print a result if it is:

#!/usr/bin/perl

%Wrestlers=(Champ=> ' CM Punk ', Chump => ' Chavo Guerrero ',

OldSkool=> ' Big John Stud ', Boof=> ' Brutus Beefcake ');

if(exists($Wrestlers{Champ}))

{ print "I see the champ!"}

Giving us a very enthusiastic:

I see the champ!

We can also use an if-else to print something out if the value does not exist, or use the if statement and the unless to achieve the same effect. Here they both are in the following examples:

#!/usr/bin/perl

%Wrestlers=(Chump => ' Chavo Guerrero ', OldSkool=> ' Big John Stud ',

Boof=> ' Brutus Beefcake ');

if(exists($Wrestlers{Champ}))

{ print "I see the champ!"}

else {print "Has anyone seen the champ?"}

or, the same result but written differently:

#!/usr/bin/perl

%Wrestlers=(Chump => ' Chavo Guerrero ', OldSkool=> ' Big John Stud ',

Boof=> ' Brutus Beefcake ');

if(exists($Wrestlers{Champ}))

{ print "I see the champ!"}