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Perl Language Reference Manual
by Larry Wall and others
Paperback (6"x9"), 724 pages
ISBN 9781906966027
RRP £29.95 ($39.95)

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29.8 H

Someone who is brilliantly persistent in solving technical problems, whether these involve golfing, fighting orcs, or programming. Hacker is a neutral term, morally speaking. Good hackers are not to be confused with evil crackers or clueless script kiddies. If you confuse them, we will presume that you are either evil or clueless.
A subroutine or method that is called by Perl when your program needs to respond to some internal event, such as a signal, or an encounter with an operator subject to operator overloading. See also callback.
hard reference
A scalar value containing the actual address of a referent, such that the referent's reference count accounts for it. (Some hard references are held internally, such as the implicit reference from one of a typeglob's variable slots to its corresponding referent.) A hard reference is different from a symbolic reference.
An unordered association of key/value pairs, stored such that you can easily use a string key to look up its associated data value. This glossary is like a hash, where the word to be defined is the key, and the definition is the value. A hash is also sometimes septisyllabically called an "associative array", which is a pretty good reason for simply calling it a "hash" instead.
hash table
A data structure used internally by Perl for implementing associative arrays (hashes) efficiently. See also bucket.
header file
A file containing certain required definitions that you must include "ahead" of the rest of your program to do certain obscure operations. A C header file has a .h extension. Perl doesn't really have header files, though historically Perl has sometimes used translated .h files with a .ph extension. See . (Header files have been superseded by the module mechanism.)
here document
So called because of a similar construct in shells that pretends that the lines following the command are a separate file to be fed to the command, up to some terminating string. In Perl, however, it's just a fancy form of quoting.
A number in base 16, "hex" for short. The digits for 10 through 16 are customarily represented by the letters a through f. Hexadecimal constants in Perl start with 0x. See also .
home directory
The directory you are put into when you log in. On a Unix system, the name is often placed into $ENV{HOME} or $ENV{LOGDIR} by login, but you can also find it with (getpwuid($<))[7]. (Some platforms do not have a concept of a home directory.)
The computer on which a program or other data resides.
Excessive pride, the sort of thing Zeus zaps you for. Also the quality that makes you write (and maintain) programs that other people won't want to say bad things about. Hence, the third great virtue of a programmer. See also laziness and impatience.
Short for a "hash value" typedef, which holds Perl's internal representation of a hash. The HV type is a subclass of SV.
ISBN 9781906966027Perl Language Reference ManualSee the print edition