Vertical bar
| Punctuation marks |
|---|
|
apostrophe (' ) |
|
ampersand ( & ) |
Vertical bar, 'Verticon', or pipe is the name of the ASCII character at position 124 (decimal). The character is depicted as either a solid vertical bar ("|") or a vertical bar with a break in the middle (broken bar "¦"). The character is usually depicted as a broken bar on IBM PC keyboards to distinguish it from other characters. However, today the "broken bar" is a separate character, U+00A6 (¦).
Usage:
Mathematics
The vertical bar is used as a mathematical symbol in
- absolute value: <math>|x|<math>, read "the absolute value of x".
- norms: <math>||(x_1,x_2)||<math>, read "the norm of x sub one, x sub two".
- set definition <math>\{x|x<2\}<math>, read "the set of x such that x is less than two". Often sets are written with a colon ':' rather than a vertical bar.
- conditional probability: <math>P(X|Y)<math>, read "the probability of X given Y".
Cursors
In text that cannot be edited but can be selected, for example, on a web page, the cursor can also be a vertical bar, possibly with little cross bars at the top and bottom.
Wiki markup
The vertical bar is used in internal links to separate a link from the displayed text. E.g., [[c programming language|C]] displays as C.
Backus-Naur form
In BNF the expression consists of sequences of symbols and/or sequences separated by '|', indicating a choice, the whole being a possible substitution for the symbol on the left.
- <personal-name> ::= <name> | <initial>
Unix
A pipe is an operating system mechanism originating in Unix which allows the output of one process to be used as input to another. Used in a shell command, this is represented by the vertical bar character. See Pipe (Unix).
Regular Expression
In regular expressions, the verticon indicates alternation. E.g., grep 'foo|bar' matches lines containing 'foo' or 'bar'.
Disjunction
In the C, perl, and many others, it is used to designate bitwise or a|b or doubled up logical or a||b.
Delimiter
Although not as common as commas or tabs, the vertical bar/pipe symbol can be used as delimiter in a flat file. An example of a pipe-delimited standard data format is LEDES 1998B.
Etymology
The name pipe for the character "|" came into common usage due to the fact that it is used in unix to pipe the output of one program into another program.