Editing File descriptor (section)

{{Short description|System resource identifier in operating systems}}
In [[Unix]] and [[Unix-like]] computer operating systems, a '''file descriptor''' ('''FD''', less frequently '''fildes''') is a process-unique identifier ([[Handle (computing)|handle]]) for a [[file (computing)|file]] or other [[input/output]] [[System resource|resource]], such as a [[pipe (Unix)|pipe]] or [[network socket]]. 

File descriptors typically have non-negative [[Integer (computer science)|integer]] values, with negative values being reserved to indicate "no value" or error conditions.

File descriptors are a part of the [[POSIX]] [[application programming interface|API]].  Each Unix [[process (computing)|process]] (except perhaps [[daemon (computer software)|daemons]]) should have three standard POSIX file descriptors, corresponding to the three [[standard streams]]:

{| class="wikitable"
!Integer value
!Name
!{{mono|&lt;[[unistd.h]]&gt;}} symbolic constant<ref>{{cite web
 | url        = http://pubs.opengroup.org/onlinepubs/9699919799/basedefs/unistd.h.html
 | title      = The Open Group Base Specifications Issue 7, IEEE Std 1003.1-2008, 2016 Edition
 | author     = The Open Group
 | access-date = 2017-09-21
 | author-link = The Open Group
 }}</ref>
!{{mono|&lt;[[stdio.h]]&gt;}} file stream<ref>{{cite web
 | url        = http://pubs.opengroup.org/onlinepubs/9699919799/basedefs/stdio.h.html
 | id         = <stdio.h>
 | title      = The Open Group Base Specifications Issue 7, IEEE Std 1003.1-2008, 2016 Edition
 | author     = The Open Group
 | access-date = 2017-09-21
 }}</ref>
|-
|0
|[[stdin|Standard input]]
|{{mono|STDIN_FILENO}}
|{{mono|stdin}}
|-
|1
|[[stdout|Standard output]]
|{{mono|STDOUT_FILENO}}
|{{mono|stdout}}
|-
|2
|[[stderr|Standard error]]
|{{mono|STDERR_FILENO}}
|{{mono|stderr}}
|}