perl] pack과 unpack을 왜 사용하는가?

사용법도 어렵지만 무엇보다 왜 쓰는지를 알아야 알아야 할지 말아야 할지를 선택할 것 아냐!!!! 헌데 정말이이 언제 어디서 무엇을 위해 사용하는것인지..생각해 봐야겠다.

참조: http://www.perlmonks.org/?node_id=224666

Pack/Unpack Tutorial

A recent conversation in the chatterbox gave me the idea to write this. A beginning programmer was trying to encode some information with pack and unpack but was having trouble coming to grips with exactly how they work. I have never had trouble with them but I came to programming from a hardware background and I'm very familiar with assembly and C programming. People who have come to programming recently have probably never dealt with things at such a low level and may not understand how a computer stores data. A little understanding at this level might make pack and unpack a little easier to figure out.

Why we need pack and unpack

Perl can handle strings, integers and floating point values. Occassionally a perl programmer will need to exchange data with programs written in other languages. These other languages have a much larger set of datatypes. They have integer values of different sizes. They may only be capable of dealing with fixed length strings (dare I say COBOL?). Sometimes, there may be a need to exchange binary data over a network with other machines. These machines may have different word sizes or even store values differently. Somehow, we need to get our data into a format that these other programs and machines can understand. We also need to be able to interpret the responses we get back.

Perl's pack and unpack functions allow us to read and write buffers of data according to a template string. The template string allows us to indicate specific byte orderings and word sizes or use the local system's default sizes and ordering. This gives us a great deal of flexibility when dealing with external programs.

In order to understand how all of this works, it helps to understand how computers store different types of information.