Science Fair Project Encyclopedia
A metasyntactic variable is a placeholder name, or a kind of alias term, commonly used to denote the subject matter under discussion, or a random member of a class of things under discussion. The term originates from computer programming and other technical contexts, and is commonly used in examples by hackers and programmers. The use of a metasyntactic variable is helpful in freeing a programmer from creating a logically named variable, although the invented term may also become sufficiently popular and enter the language as a neologism. The word foo is the canonical example.
Metasyntactic variables are so called because:
- they are variables in the metalanguage used to talk about programs, etc. (see also pseudocode);
- 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 'cool': the term is an example of computer jargon.
Foo, Bar and Baz
Foo is the first metasyntactic variable, commonly used to represent an as-yet-unspecified term, value, process, function, destination or event but seldom a person (see Ned Baker, below). It is sometimes combined with bar to make foobar. This suggests that foo may have originated with the World War II slang term fubar, as an acronym for fucked/fouled up beyond all recognition, although the Jargon File makes a reasonably good case  that foo predates fubar. Foo was also used as a nonsense word in the surrealistic comic strip Smokey Stover that was popular in the 1940s and 1950s. It is used in irc as a form of mockery, often in the form F00, and sometimes explained as a shortening of fool. It appears to be unrelated to Kung fu. See also Foo fighter for more foo etymology, as well as RFC 3092.
Bar, the canonical second metasyntactic variable, typically follows foo.
Baz, the canonical third metasyntactic variable, is commonly used after foo and bar.
Quux is the canonical fourth metasyntactic variable, commonly used after baz. However more recently Qux has become more common as the fourth variable, displacing Quux as the fifth. A probable reason for this is that Quux is often followed by the series Quuux, Quuuux, Quuuuux etc. and Qux fits this pattern perfectly.
Bat is used by some programmers as an alternative to quux.
Spam and Eggs
Needle and Haystack
Needle and haystack are commonly used in computer programming to describe the syntax of functions that involve a search parameter and a search target, such as searching a substring within a string; with these two words, derived from the idiom "to find a needle in a haystack", it is clearer where the substring to search for goes, and where the string to search in goes. This can be seen, for instance, in the documentation for some functions in the computer language, PHP .
Other words used as metasyntactic variables include: test, mum, thud, beekeeper, hoge, corge, grault, garply, waldo, plugh, kalaa, puppu, dothestuff, temp, var, sub, glarb, blarg.
The number 23 is also commonly used as an integer example --particularly when the connotations associated with 42 are undesirable.
The number 42 is often a common initializer for integer variables, and acts as in the same vein as a "metasyntactic value". It is taken from Douglas Adams' The Hitchhiker's Guide to the Galaxy, where Deep Thought concluded that it was The Answer to Life, the Universe, and Everything.
69 is often used as an example number. Popular among hackers as an addition to metasyntactic variables (foo69, bar69), also used in all sorts of hacks. It is also a largest number whose factorial can be calculated by a pocket calculator limited to standard scientific notation with a 2 digit exponent.
0815 is used in German as either a random number or to reflect something normal or boring.
Stands for Leet, in Leetspeak, being, thus, commonly used.
6858 is the self-destruct code for the Star Generator in the game Space Quest. At least one programmer has been known to use this as a meta-syntactic or magic number.
Names of people
J. Random and Ned Baker
Alice and Bob
- Carol - a participant in three- and four-party protocols
- Dave - a participant in four-party protocols
- Ellen - a participant in five- and six-party protocols
- Frank - a participant in six-party protocols, and so on
- Eve or Oscar - an (evil) eavesdropper
- Mallory or Mallet - a malicious active attacker
- Trent - a trusted arbitrator
- Walter - a warden
- Peggy - a prover
- Victor - a verifier
- Sam - a trusted server (Uncle Sam)
- Charlie - a challenger or opponent
- Trudy - an intruder or malicious entity
Bob, Alice and Carol may have come from the 1969 movie Bob & Carol & Ted & Alice, or from the fact that they are common English names starting with A, B and C, the first letters of the alphabet. Dave, Ellen, and Frank are the next three letters. Some people continue this pattern, using Greg or another similar term for the seventh participant, and so on.
Fred and Barney
After the characters in the cartoon series The Flintstones. The most famous use of these is the example code in Learning Perl. Fred is also known to have been used simply because the keys are close together on the QWERTY keyboard.
Sometimes placeholders from other contexts will be used: John Doe, Jane Roe, Richard Roe, A. N. Other, John Q. Public, and Bloggs or Joe Bloggs. Other nonsense names come from swapping initials, e.g. J. Pennings .
Other languages sometimes have their own metasyntactic variables. For example:
- Jia, Yi, Bing, Ding - from Chinese
- flaf, giraf, boing - from Danish
- Aap, Noot, Mies - from Dutch
- pippo, pluto, paperino (Italian names of the Disney characters Goofy, Pluto and Donald Duck) - from Italian
- Maria Bernasconi - from Italian in Switzerland
- toto, tata, titi - from French
- koko, lala, malakia - from Greek
- hoge, hogehoge, moge - from Japanese
- peh, meh, shmeh - from Yiddish
- bla, la - from Portuguese
- huu, haa - from Finnish
- hahaa, hihii, hohoo - also from Finnish
- kalatehas (fish factory) - from Estonian
- muh, bla, blubb, schlurps, schnurz, Lieschen Mueller - from German
- bubu, mumu, zeze - from Romanian
- brol, prout - from French in Belgium
- filan, hede, hödö, zıvır, ıvır - from Turkish
- fulano, mengano, zutano, pepe (Joe), pp (phonetic equivalent), coso (in Argentina, "coso" can be anything, but usually refers to some physical object) - from Spanish
- Ploni (פלוני) in Hebrew (as a person's name)
- The Jargon File entry on Foo
- RFC 3092 - The IETF memo on Foo (note that this is an April Fool's Day RFC memo)
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