Editing Vertical bar (section)

===Computing===

==== Pipe ====
{{Main|Pipeline (Unix)}}

A [[pipe (Unix)|pipe]] is an [[inter-process communication]] mechanism originating in [[Unix]], which directs the output (standard out and, optionally, standard error) of one process to the input (standard in) of another. In this way, a series of commands can be "piped" together, giving users the ability to quickly perform complex multi-stage processing from the [[Command-line interface|command line]] or as part of a [[UNIX shell script|Unix shell script]] ("bash file"). In most [[Unix shell]]s (command interpreters), this is represented by the vertical bar character. For example:

<code> [[grep]] -i 'blair' filename.log | [[More (command)#Unix|more]] </code>

where the output from the <kbd>grep</kbd> process (all lines containing 'blair') is piped to the <kbd>more</kbd> process (which allows a command line user to read through results one page at a time).

The same "pipe" feature is also found in later versions of [[DOS]] and Microsoft Windows.

This usage has led to the character itself being called "pipe".

====Disjunction====
In many programming languages, the vertical bar is used to designate the [[Logical disjunction|logic operation ''or'']], either [[Bitwise operation|bitwise]] ''or'' or [[Boolean data type|logical]] ''or''.

Specifically, in [[C (programming language)|C]] and other languages following [[C syntax]] conventions, such as [[C++]], [[Perl]], [[Java (programming language)|Java]] and [[C Sharp (programming language)|C#]], <code>a | b</code> denotes a [[Bitwise operation#OR|bitwise ''or'']]; whereas a double vertical bar <code>a || b</code> denotes a ([[Minimal evaluation|short-circuited]]) [[logical disjunction|logical ''or'']]. Since the character was originally not available in all [[code page]]s and keyboard layouts, [[ANSI C]] can transcribe it in form of the [[C trigraph|trigraph]] <code>??!</code>, which, outside string literals, is equivalent to the <code>|</code> character.

In [[regular expression]] syntax, the vertical bar again indicates logical ''or'' ([[alternation (formal language theory)|alternation]]). For example: the Unix command <code>[[grep]] -E 'fu|bar'</code> matches lines containing 'fu' or 'bar'.

====Concatenation====
The double vertical bar operator "||" denotes [[string (computer science)|string]] [[concatenation]] in [[PL/I]], [[Rexx|REXX]], [[Object REXX|ooRexx]], standard [[ANSI SQL]], and theoretical computer science (particularly [[cryptography]]).

====Delimiter====
Although not as common as commas or tabs, the vertical bar can be used as a [[delimiter]] in a [[flat file]]. Examples of a [[pipe delimited|pipe-delimited]] standard data format are [[LEDES]] 1998B and [[HL7]]. It is frequently used because vertical bars are typically uncommon in the data itself.

Similarly, the vertical bar may see use as a delimiter for [[regular expression]] operations (e.g. in [[sed]]). This is useful when the regular expression contains instances of the more common forward slash (<code>/</code>) delimiter; using a vertical bar eliminates the need to escape all instances of the forward slash. However, this makes the bar unusable as the regular expression "alternative" operator.

====Backus–Naur form====
In [[Backus–Naur form]], an expression consists of sequences of symbols and/or sequences separated by '|', indicating a [[Alternation (formal language theory)|choice]], the whole being a possible substitution for the symbol on the left.
{{sxhl|2=bnf|1=<personal-name> ::= <name> {{!}} <initial>}}

====Concurrency operator====
In calculi of communicating processes (like [[pi-calculus]]), the vertical bar is used to indicate that processes execute in parallel.

====APL====
The pipe in [[APL (programming language)|APL]] is the modulo or ''residue'' function between two operands and the absolute value function next to one operand.

====List comprehensions====
{{Main|List comprehensions}}

The vertical bar is used for list comprehensions in some functional languages, e.g. [[Haskell (programming language)|Haskell]] and [[Erlang (programming language)|Erlang]]. Compare [[#Mathematics|set-builder notation]].

====Text markup====

The vertical bar is used as a special character in [[lightweight markup language]]s, notably [[MediaWiki]]'s [[Wikitext]] (in the templates and internal links).

In LaTeX text mode, the vertical bar produces an [[em dash]] (—). The <code>\textbar</code> command can be used to produce a vertical bar.