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metasyntactic variable: n. A name used in examples and understood to stand for whatever thing
is under discussion, or any random member of a class of things under
discussion. The word foo is the
canonical example. To avoid confusion, hackers
never (well, hardly ever) use ‘foo’ or other words like it as
permanent names for anything. In filenames, a common convention is that
any filename beginning with a metasyntactic-variable name is a
scratch file that may be deleted at any time. Metasyntactic variables are so called because (1) they are variables
in the metalanguage used to talk about programs etc; (2) they are variables
whose values are often variables (as in usages like “the value of
f(foo,bar) is the sum of foo and bar”). However, it has been
plausibly suggested that the real reason for the term “metasyntactic
variable” is that it sounds good. To some extent, the list of one's
preferred metasyntactic variables is a cultural signature. They occur both
in series (used for related groups of variables or objects) and as
singletons. Here are a few common signatures: Of all these,
only foo and bar are universal (and
baz nearly so). The compounds
foobar and foobaz also enjoy very wide currency. Some
jargon terms are also used as metasyntactic names;
barf and mumble, for example.
See also Commonwealth Hackish for discussion of
numerous metasyntactic variables found in Great Britain and the
Commonwealth.
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