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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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29.18 R

readable
With respect to files, one that has the proper permission bit set to let you access the file. With respect to computer programs, one that's written well enough that someone has a chance of figuring out what it's trying to do.
reaping
The last rites performed by a parent process on behalf of a deceased child process so that it doesn't remain a zombie. See the wait ( ) and waitpid ( ) function calls.
record
A set of related data values in a file or stream, often associated with a unique key field. In Unix, often commensurate with a line, or a blank-line-terminated set of lines (a "paragraph"). Each line of the /etc/passwd file is a record, keyed on login name, containing information about that user.
recursion
The art of defining something (at least partly) in terms of itself, which is a naughty no-no in dictionaries but often works out okay in computer programs if you're careful not to recurse forever, which is like an infinite loop with more spectacular failure modes.
reference
Where you look to find a pointer to information somewhere else. (See indirection.) References come in two flavors, symbolic references and hard references.
referent
Whatever a reference refers to, which may or may not have a name. Common types of referents include scalars, arrays, hashes, and subroutines.
regex
See regular expression.
regular expression
A single entity with various interpretations, like an elephant. To a computer scientist, it's a grammar for a little language in which some strings are legal and others aren't. To normal people, it's a pattern you can use to find what you're looking for when it varies from case to case. Perl's regular expressions are far from regular in the theoretical sense, but in regular use they work quite well. Here's a regular expression: /Oh s.*t./. This will match strings like "Oh say can you see by the dawn's early light" and "Oh sit!". See 11.
regular expression modifier
An option on a pattern or substitution, such as /i to render the pattern case insensitive. See also cloister.
regular file
A file that's not a directory, a device, a named pipe or socket, or a symbolic link. Perl uses the -f file test operator to identify regular files. Sometimes called a "plain" file.
relational operator
An operator that says whether a particular ordering relationship is true about a pair of operands. Perl has both numeric and string relational operators. See collating sequence.
reserved words
A word with a specific, built-in meaning to a compiler, such as if or delete ( ). In many languages (not Perl), it's illegal to use reserved words to name anything else. (Which is why they're reserved, after all.) In Perl, you just can't use them to name labels or filehandles. Also called "keywords".
return value
The value produced by a subroutine or expression when evaluated. In Perl, a return value may be either a list or a scalar.
RFC
Request For Comment, which despite the timid connotations is the name of a series of important standards documents.
right shift
A bit shift that divides a number by some power of 2.
root
The superuser (UID == 0). Also, the top-level directory of the filesystem.
RTFM
What you are told when someone thinks you should Read The Fine Manual.
run phase
Any time after Perl starts running your main program. See also compile phase. Run phase is mostly spent in run time but may also be spent in compile time when require ( ), do ( ) FILE, or eval ( ) STRING operators are executed or when a substitution uses the /ee modifier.
run time
The time when Perl is actually doing what your code says to do, as opposed to the earlier period of time when it was trying to figure out whether what you said made any sense whatsoever, which is compile time.
run-time pattern
A pattern that contains one or more variables to be interpolated before parsing the pattern as a regular expression, and that therefore cannot be analyzed at compile time, but must be re-analyzed each time the pattern match operator is evaluated. Run-time patterns are useful but expensive.
RV
A recreational vehicle, not to be confused with vehicular recreation. RV also means an internal Reference Value of the type a scalar can hold. See also IV and NV if you're not confused yet.
rvalue
A value that you might find on the right side of an assignment. See also lvalue.
ISBN 9781906966027Perl Language Reference ManualSee the print edition