A metasyntactic variable can either be a placeholder name, 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.
The phenomenon is similar to the use in algebra of x, y and z for unknown variables, and a, b and c for unknown constants. "Widgets" are also used in business to indicate an as-yet-unspecified product and are frequently sold by the Acme company.
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").
- 1 Examples
- 1.1 Nonsense words
- 1.2 English words
- 1.3 Numbers
- 1.4 Names of people
- 1.5 Place names
- 1.6 Images
- 2 Other languages
- 3 See also
- 4 External links
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/repair, 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. See also Foo fighter for more foo etymology, as well as RFC 3092. Another usage of foo is as an abreviation of the phrase "forward observation officer" (or observer). Apparently FOOs used to go places well forward of normal troops in battle and leave a stylised chalk graffiti of a person looking over a wall with the words "foo was here".
The term "Kung foo" has come to mean skill in computer programming. This is actually used (though misspelled) in the movie The Core. This usage itself has spawned variants, such as the GIMP's "Script-Fu" plugin.
Bar, the canonical second metasyntactic variable, typically follows foo.
Baz, the canonical third metasyntactic variable, is commonly used after foo and bar.
Foo, bar, and baz are often compounded together to make such words as foobar, barbaz, and foobaz.
Gazonk is often used as an alternative for baz or as a fourth metasyntactic variable. Some early versions of the popular editor Emacs used gazonk.foo as a default filename.
Quux, introduced by Guy L. Steele, Jr., 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 quuux.
Infrequently used in various environments such as Berkeley, GeoWorks, Ingres, Quovadx. Pronounced /shmeh/ with a short /e/.
hukarz (pronounced who cares) is sometimes used by certain functional programmers, e.g., to initialise variables in untyped languages when the value assigned to the variable is immaterial but it is necessary to declare the variable.
RFC 3092 gives the "standard list of metasyntactic variables" as follows:
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 for which to search goes, and where the string in which to search goes. This can be seen, for instance, in the documentation for some functions in the computer language PHP, see  for an example.
Other words used as metasyntactic variables include: beekeeper, blah, blarg, bleh, corge, doip, dothestuff, garply, glarb, grault, hoge, kalaa, mum, plugh, puppu, stuff, sub, temp, test, thud, var, waldo, momo.
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 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. 69 is popular because of its reference to a sexual position. It is also because it is the largest number whose factorial can be calculated by a pocket calculator limited to standard scientific notation with a 2 digit exponent.
Stands for Leet, in Leetspeak, being, thus, commonly used.
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 Gloria or another similar term for the seventh participant, and so on (maintaining the pattern female, male, female, male...).
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.
Some names are most commonly used in military context.
- Private Snuffy
- Susie Rottencrotch or Jane Rottencrotch from the movie Full Metal Jacket
- GI Joe or GI Jane
- Beetle Bailey from the comic strip of the same name
- Gomer Pyle or Private Pyle from the television show of the same name, also popularized by the movie Full Metal Jacket
- Tommy Atkins, origin of the name "Tommy" for a British soldier
- Private Bloggins, used primarily within the Canadian Forces as an arbitrary person, much like John Smith.
Sometimes placeholders from other contexts will be used: John Doe, Jane Roe, Richard Roe, A. N. Other, John Q. Public, Bloggs or Joe Bloggs, Joe Soap and Tom, Dick and Harry. In some law schools, the generic case name Push v. Pull is used as a variable. Law or accounting firms are sometimes referred to with names like Dewey, Cheatem, and Howe ("Do we cheat 'em, and how!") Other nonsense names come from swapping initials, e.g. J. Pennings.
Smallville and Metropolis
Anywhere, Anytown and Nowhere
Anywhere, USA or Anytown, USA connotes genericness. Nowhere sometimes suggests that the entry is invalid.
Middle of Nowhere / In the Sticks / East Buttf-ck / East Boofu
Unlike Nowhere, these metasyntactic variables indicate extreme remoteness and suggest contempt.
This term is sometimes a placeholder for a generic university.
Y.U. Bum University
This term is sometimes a placeholder for a less generic university. Pronounced like "Why you bum, you."
Other languages sometimes have their own metasyntactic variables. For example:
- Jia, Yi, Bing, Ding - from Chinese
- flaf, giraf, boing - from Danish
- aap, noot, mies, Piet, Jan, Kees - from Dutch
- pippo, pluto, paperino, topolino (Italian names of the Disney characters Goofy, Pluto, Donald Duck and Mickey Mouse) - from Italian
- Maria Bernasconi - from Italian in Switzerland
- toto, tata, titi, prout, banane - from French
- koko, lala, malakia - from Greek
- hoge, hogehoge, moge, huga, piyo, chomechome, nyoronyoro, naninani - from Japanese
- peh, meh, shmeh - from Yiddish
- bla, nha, la, patati, patata, Fulano, Sicrano and Beltrano (the last three as placeholders for persons' names) - from Portuguese
- huu, haa - from Finnish
- hahaa, hihii, hohoo - also from Finnish
- kala (fish), kalatehas (fish factory), oxe (misspelled vomit) - from Estonian
- muh, bla, blubb, schlurps, schnurz, Lieschen Mueller, Hinz & Kunz, Otto Normalverbraucher - from German
- bubu, mumu, zeze - from Romanian
- brol, prout - from French in Belgium
- filan, hede, hödö, zıvır, ıvır, bok, püsür, ali, veli, deli - from Turkish
- fulano, mengano, zutano (the three used to denote a supposed or fictional person), sultano (variant of the previously mentioned "zutano"), pepe (Joe), pp (phonetic equivalent to "pepe"), vaina, (vulgar) cosa (in Spanish, "cosa" can be anything, but usually refers to some physical object), pirola (has no meaning) pirolita (literally, "small pirola"; has no meaning) - from Spanish
- Ploni (פלוני) as a person's name; Reuven (ראובן) and Shim'on (שמעון) as two persons (after Jacob's Sons)- from Hebrew
- Kuppuswamy, Ramaswamy - from Tamil
- Gipsz Jakab; alma, körte, barack, lófasz - from Hungarian
- Phalaan Phalaan - from Hindi
- Vasya Pupkin, Private Pupkin (Вася Пупкин, рядовой Пупкин), meaning abstract person, but generally a soldier or a programmer - from Russian
- bla, blahuj, ugg, ugga, blargh, gunk, tjo, bork; Kalle, Olle, Pelle, Nisse (the diminutives of Karl, Olof, Per and Nils respectively) - Swedish
- duvelacky can be used for widget - Australian English
It may also be interesting to note that lazy programmers who run out of nonsense words simply append numbers when they need more variables.
- The Jargon File entry on Foo, and also the entry on Commonwealth Hackish for non-US English words such as "wombat".
- RFC 3092 - The IETF memo on Foo (note that this is an April Fool's Day RFC memo)
- Acme::MetaSyntactic A Perl module providing metasyntactic variable names. Updated weekly.