gloss.htm

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<dt>export</dt>
<dd>
<p>
<a name="INDEX-"></a>
To make symbols from a <em class="emphasis">module</em> available for <em class="emphasis">import</em> by other modules.
</p>
</dd>
</dl>

<dl>
<dt>expression</dt>
<dd>
<p>
<a name="INDEX-"></a>
Anything you can legally say in a spot where a <em class="emphasis">value</em> is required.
Typically composed of <em class="emphasis">literals</em>, <em class="emphasis">variables</em>, <em class="emphasis">operators</em>,
<em class="emphasis">functions</em>, and <em class="emphasis">subroutine</em> calls, not necessarily in that order.
</p>
</dd>
</dl>

<dl>
<dt>extension</dt>
<dd>
<p>
<a name="INDEX-"></a>
A Perl module that also pulls in compiled C or C++ code.  More
generally, any experimental option that can be compiled into Perl, such
as multithreading.
</p>
</dd>
</dl>

<dl>
<dt>false</dt>
<dd>
<p>
<a name="INDEX-"></a><a name="INDEX-"></a>
In Perl, any value that would look like <tt class="literal">""</tt> or <tt class="literal">"0"</tt> if
evaluated in a string context.  Since undefined values evaluate to
<tt class="literal">""</tt>, all undefined values are false, but not all false values
are undefined.
</p>
</dd>
</dl>

<dl>
<dt>FAQ</dt>
<dd>
<p>
Frequently Asked Question (although not necessarily frequently
answered, especially if the answer appears in the Perl FAQ
shipped standard with Perl).
</p>
</dd>
</dl>

<dl>
<dt>fatal error</dt>
<dd>
<p>
<a name="INDEX-"></a><a name="INDEX-"></a><a name="INDEX-"></a>
An uncaught <em class="emphasis">exception</em>, which causes termination
of the <em class="emphasis">process</em> after printing a message on your
<em class="emphasis">standard error</em> stream.  Errors that happen inside
an <tt class="literal">eval</tt> are not fatal.  Instead, the
<tt class="literal">eval</tt> terminates after placing the exception message
in the <tt class="literal">$@</tt> (<tt class="literal">$EVAL_ERROR</tt>)
variable.  You can try to provoke a fatal error with the
<tt class="literal">die</tt>
operator (known as throwing or raising an exception), but this may be
caught by a dynamically enclosing <tt class="literal">eval</tt>.  If not
caught, the <tt class="literal">die</tt> becomes a fatal error.
</p>
</dd>
</dl>

<dl>
<dt>field</dt>
<dd>
<p>
<a name="INDEX-"></a><a name="INDEX-"></a><a name="INDEX-"></a>
A single piece of numeric or string data that is part of a longer
<em class="emphasis">string</em>, <em class="emphasis">record</em>, or <em class="emphasis">line</em>.  Variable-width fields are usually
split up by <em class="emphasis">separators</em> (so use <tt class="literal">split</tt> to extract the fields),
while fixed-width fields are usually at fixed positions (so use
<tt class="literal">unpack</tt>).  <em class="emphasis">Instance variables</em> are also known as "fields".
</p>
</dd>
</dl>

<dl>
<dt>FIFO</dt>
<dd>
<p>
<a name="INDEX-"></a>
First In, First Out.  See also <em class="emphasis">LIFO</em>.  Also,
a nickname for a <em class="emphasis">named pipe</em>.
</p>
</dd>
</dl>

<dl>
<dt>file</dt>
<dd>
<p>
<a name="INDEX-"></a><a name="INDEX-"></a>
A named collection of data, usually stored on disk in a
<em class="emphasis">directory</em> in a <em class="emphasis">filesystem</em>.
Roughly like a document, if you're into office metaphors.  In modern
filesystems, you can actually give a file more than one name.  Some
files have special properties, like directories and devices.
</p>
</dd>
</dl>

<dl>
<dt>file descriptor</dt>
<dd>
<p>
<a name="INDEX-"></a>
The little number the <em class="emphasis">operating system</em> uses to
keep track of which opened <em class="emphasis">file</em> you're talking
about.  Perl hides the file descriptor inside a <em class="emphasis">standard
I/O</em> stream and then attaches the stream to a
<em class="emphasis">filehandle</em>.
</p>
</dd>
</dl>

<dl>
<dt>file test operator</dt>
<dd>
<p>
<a name="INDEX-"></a>
A built-in unary operator that you use to determine whether something
is <em class="emphasis">true</em> about a file, such as <tt class="literal">-o $filename</tt> to test whether
you're the owner of the file.
</p>
</dd>
</dl>

<dl>
<dt>fileglob</dt>
<dd>
<p>
A "wildcard" match on <em class="emphasis">filenames</em>.  See the <tt class="literal">glob</tt> function.
</p>
</dd>
</dl>

<dl>
<dt>filehandle</dt>
<dd>
<p>
<a name="INDEX-"></a>
An identifier (not necessarily related to the real name of a file)
that represents a particular instance of opening a file until you
close it.  If you're going to open and close several different
files in succession, it's fine to open each of them with the
same filehandle, so you don't have to write out separate code to
process each file.
</p>
</dd>
</dl>

<dl>
<dt>filename</dt>
<dd>
<p>
<a name="INDEX-"></a>
One name for a file.  This name is listed in a <em class="emphasis">directory</em>, and
you can use it in an <tt class="literal">open</tt> to tell the <em class="emphasis">operating
system</em> exactly which file you want to open, and associate the
file with a <em class="emphasis">filehandle</em> which will carry the subsequent identity of
that file in your program, until you close it.
</p>
</dd>
</dl>

<dl>
<dt>filesystem</dt>
<dd>
<p>
<a name="INDEX-"></a>
A set of <em class="emphasis">directories</em> and <em class="emphasis">files</em> residing on a partition of the
disk.  Sometimes known as a "partition".  You can change the file's
name or even move a file around from directory to directory within
a filesystem without actually moving the file itself, at least under
Unix.
</p>
</dd>
</dl>

<dl>
<dt>filter</dt>
<dd>
<p>
<a name="INDEX-"></a>
A program designed to take a <em class="emphasis">stream</em> of input
and transform it into a stream of output.
</p>
</dd>
</dl>

<dl>
<dt>flag</dt>
<dd>
<p>
<a name="INDEX-"></a><a name="INDEX-"></a>
We tend to avoid this term because it means so many things.  It may
mean a command-line <em class="emphasis">switch</em> that takes no argument
itself (such as Perl's <span class="option">-n</span> and <span class="option">-p</span>
flags) or, less frequently, a single-bit indicator (such as the
<tt class="literal">O_CREAT</tt> and <tt class="literal">O_EXCL</tt> flags used in
<tt class="literal">sysopen</tt>).
</p>
</dd>
</dl>

<dl>
<dt>floating point</dt>
<dd>
<p>
<a name="INDEX-"></a><a name="INDEX-"></a>
A method of storing numbers in "scientific notation", such that the
precision of the number is independent of its magnitude (the decimal
point "floats").  Perl does its numeric work with floating-point
numbers (sometimes called "floats"), when it can't get away with
using <em class="emphasis">integers</em>.  Floating-point numbers are mere
approximations of real numbers.
</p>
</dd>
</dl>

<dl>
<dt>flush</dt>
<dd>
<p>
<a name="INDEX-"></a>
The act of emptying a <em class="emphasis">buffer</em>, often before it's full.
</p>
</dd>
</dl>

<dl>
<dt>FMTEYEWTK</dt>
<dd>
<p>
<a name="INDEX-"></a>
Far More Than Everything You Ever Wanted To Know.  An exhaustive
treatise on one narrow topic, something of a
super-<em class="emphasis">FAQ</em>.  See Tom for far more.
</p>
</dd>
</dl>

<dl>
<dt>fork</dt>
<dd>
<p>
<a name="INDEX-"></a>
To create a child <em class="emphasis">process</em> identical to the parent
process at its
moment of conception, at least until it gets ideas of its own.
A thread with protected memory.
</p>
</dd>
</dl>

<dl>
<dt>formal arguments</dt>
<dd>
<p>
<a name="INDEX-"></a><a name="INDEX-"></a><a name="INDEX-"></a>
The generic names by which a <em class="emphasis">subroutine</em> knows its
<em class="emphasis">arguments</em>.  In many languages, formal
arguments are always given individual names, but in Perl, the formal
arguments are just the elements of an array.  The formal arguments to
a Perl program are <tt class="literal">$ARGV[0]</tt>,
<tt class="literal">$ARGV[1]</tt>, and so on.  Similarly, the formal
arguments to a Perl subroutine are <tt class="literal">$_[0]</tt>,
<tt class="literal">$_[1]</tt>, and so on.  You may give the arguments
individual names by assigning the values to a 
<tt class="literal">my</tt> list.  See also <em class="emphasis">actual
arguments</em>.
</p>
</dd>
</dl>

<dl>
<dt>format</dt>
<dd>
<p>
<a name="INDEX-"></a>
A specification of how many spaces and digits and things to put somewhere
so that whatever you're printing comes out nice and pretty.
</p>
</dd>
</dl>

<dl>
<dt>freely available</dt>
<dd>
<p>
Means you don't have to pay money to get it, but the copyright on it may
still belong to someone else (like Larry).
</p>
</dd>
</dl>

<dl>
<dt>freely redistributable</dt>
<dd>
<p>
Means you're not in legal trouble if you give a bootleg copy of it to
your friends and we find out about it.  In fact, we'd rather you gave
a copy to all your friends.
</p>
</dd>
</dl>

<dl>
<dt>freeware</dt>
<dd>
<p>
<a name="INDEX-"></a>
Historically, any software that you give away, particularly if you make
the source code available as well.  Now often called <em class="emphasis">open source
software</em>.  Recently there has been a trend to use the term
in contradistinction to <em class="emphasis">open source software</em>, to refer only to free
software released under the Free Software Foundation's GPL (General
Public License), but this is difficult to justify etymologically.
</p>
</dd>
</dl>

<dl>
<dt>function</dt>
<dd>
<p>
<a name="INDEX-"></a>
Mathematically, a mapping of each of a set of input values to a particular
output value.  In computers, refers to a <em class="emphasis">subroutine</em> or
<em class="emphasis">operator</em> that returns a <em class="emphasis">value</em>.  It may or may not have
input values (called <em class="emphasis">arguments</em>).
</p>
</dd>
</dl>

<dl>
<dt>funny character</dt>
<dd>
<p>
<a name="INDEX-"></a><a name="INDEX-"></a>
Someone like Larry, or one of his peculiar friends.  Also refers to the
strange prefixes that Perl requires as noun markers on its variables.
</p>
</dd>
</dl>

<dl>
<dt>garbage collection</dt>
<dd>
<p>
<a name="INDEX-"></a>
A misnamed feature--it should be called, "expecting your mother to pick
up after you".  Strictly speaking, Perl doesn't do this, but it relies on
a reference-counting mechanism to keep things tidy.  However, we rarely
speak strictly and will often refer to the reference-counting scheme
as a form of garbage collection.  (If it's any comfort, when your
interpreter exits, a "real" garbage collector runs to make sure
everything is cleaned up if you've been messy with circular references
and such.)
</p>
</dd>
</dl>

<dl>
<dt>GID</dt>
<dd>
<p>
<a name="INDEX-"></a><a name="INDEX-"></a>
Group ID--in Unix, the numeric group ID that the <em class="emphasis">operating
system</em> uses to identify you and members of your <em class="emphasis">group</em>.
</p>
</dd>
</dl>

<dl>
<dt>glob</dt>
<dd>
<p>
<a name="INDEX-"></a>
Strictly, the shell's <tt class="literal">*</tt> character,
which will match a "glob" of
characters when you're trying to generate a list of filenames.  Loosely,
the act of using globs and similar symbols to do pattern matching.
See also <em class="emphasis">fileglob</em> and <em class="emphasis">typeglob</em>.
</p>
</dd>
</dl>

<dl>
<dt>global</dt>
<dd>
<p>
<a name="INDEX-"></a><a name="INDEX-"></a>
Something you can see from anywhere, usually used of
<em class="emphasis">variables</em> and
<em class="emphasis">subroutines</em> that are visible everywhere
in your program.  In Perl, only
certain special variables are truly global--most variables (and all
subroutines) exist only in the current
<em class="emphasis">package</em>.  Global variables
can be declared with <tt class="literal">our</tt>.  See 
"Global Declarations" in
<a href="ch04_01.htm">Chapter 4, "Statements and Declarations"</a>.
</p>
</dd>
</dl>

<dl>
<dt>global destruction</dt>
<dd>
<p>
The <em class="emphasis">garbage collection</em> of globals (and the running of any associated
object destructors) that takes place when a Perl <em class="emphasis">interpreter</em> is
being shut down.  Global destruction should not be confused with the
Apocalypse, except perhaps when it should.
</p>
</dd>
</dl>


<dl>
<dt>glue language</dt>
<dd>
<p>
<a name="INDEX-"></a>
A language such as Perl that is good at hooking things together
that weren't intended to be hooked together.
</p>
</dd>
</dl>


<dl>
<dt>granularity</dt>
<dd>
<p>
The size of the pieces you're dealing with, mentally speaking.
</p>
</dd>
</dl>


<dl>
<dt>greedy</dt>
<dd>
<p>
<a name="INDEX-"></a>
A <em class="emphasis">subpattern</em> whose <em class="emphasis">quantifier</em>
wants to match as many things as possible.
</p>
</dd>
</dl>

<dl>
<dt>grep</dt>
<dd>
<p>
<a name="INDEX-"></a>
Originally from the old Unix editor command for "Globally search for
a Regular Expression and Print it", now used in the general
sense of any kind of search, especially text searches.  Perl has a
built-in <tt class="literal">grep</tt> function that searches a list for
elements matching any given criterion, whereas the 
<em class="emphasis">grep</em>(1) program searches for lines
matching a <em class="emphasis">regular expression</em> in one or more files.
</p>
</dd>
</dl>

<dl>
<dt>group</dt>
<dd>
<p>
<a name="INDEX-"></a><a name="INDEX-"></a><a name="INDEX-"></a>
A set of users of which you are a member.  In some operating
systems (like Un