Editing Cd (command) (section)

== Implementations ==
Generally, a computer system that provides access to a [[hierarchical file system]], provides a change directory command to set the working directory. As this applies to most operating system shells, most support a change directory command, including [[Unix]] and [[Unix-like]] (i.e. [[Linux]]) [[Unix shell|shells]], and [[Microsoft]] shells including [[Command Prompt]] and [[PowerShell]].

Other operating systems with shells supporting the command include [[OS/2]],<ref>{{cite web|url=http://www.jatomes.com/Help/Os2Cmd.php#CD|title=JaTomes Help – OS/2 Commands|website=www.jatomes.com|access-date=2019-08-11|archive-date=2019-04-14|archive-url=https://web.archive.org/web/20190414130029/http://www.jatomes.com/Help/Os2Cmd.php#CD|url-status=dead}}</ref> [[TRIPOS]],<ref>{{cite web|url=https://www.pagetable.com/docs/amigados_tripos/tripos_manuals.pdf |title=Introduction to Tripos |access-date=2020-05-01}}</ref> [[AmigaOS]]<ref>{{cite book|url=http://archive.org/details/1988-rugheimer-spanik-amigados-quick-reference|title=AmigaDOS quick reference|first1=Hannes|last1=Rügheimer|first2=Christian|last2=Spanik|date=May 1, 1988|publisher=Grand Rapids, Mi : Abacus|isbn=9781557550491|via=Internet Archive}}</ref> (where the command is implied for an input [[Path (computing)|path]]), [[ReactOS]],<ref>{{cite web|url=https://github.com/reactos/reactos/blob/master/base/shell/cmd/internal.c|title=Reactos/reactos|website=GitHub|date=3 January 2022}}</ref> [[DOSBox]], and [[Unified Extensible Firmware Interface|UEFI]].<ref name="EFI-Shells-and-Scripting">{{cite web
 | url = http://software.intel.com/en-us/articles/efi-shells-and-scripting/
 | title = EFI Shells and Scripting
 | publisher = [[Intel]]
 | access-date = 2013-09-25
}}</ref> 

* On [[MS-DOS]], the command is available in version 2 and later<ref name="RUNNINGMSDOS">{{Cite book|author-last=Wolverton|author-first=Van|title=Running MS-DOS Version 6.22 (20th Anniversary Edition), 6th Revised edition|date=2003|publisher=[[Microsoft Press]]|isbn=0-7356-1812-7}}</ref> 
* [[DR DOS 6.0]] includes the command as both {{code|cd}} and {{code|chdir}}<ref name="drdos6userguide">{{Cite web |url=https://www.4corn.co.uk/archive/docs/DR%20DOS%206.0%20User%20Guide-opt.pdf |title=DR DOS 6.0 User Guide Optimisation and Configuration Tips |access-date=2019-08-13 |archive-url=https://web.archive.org/web/20190930135943/http://www.4corn.co.uk/archive/docs/DR%20DOS%206.0%20User%20Guide-opt.pdf |archive-date=2019-09-30 |url-status=dead }}</ref>
* On [[Hewlett-Packard|HP]] [[HP Multi-Programming Executive|MPE/iX]] the command is {{code|chdir}}<ref>{{Cite web|url=http://www.teamnaconsulting.com/compresources/pdfs/c01687363.pdf|title=MPE/iX Command Reference Manual|access-date=2018-10-21|archive-date=2018-10-21|archive-url=https://web.archive.org/web/20181021232213/http://www.teamnaconsulting.com/compresources/pdfs/c01687363.pdf|url-status=dead}}</ref> 
* On [[Stratus VOS|OpenVOS]], the command is {{code|change_current_dir}}<ref>{{cite web |url=http://stratadoc.stratus.com/vos/19.1.0/r098-19/wwhelp/wwhimpl/common/html/r098-19.pdf |title= OpenVOS Commands Reference Manual |website=stratadoc.stratus.com |access-date=2020-09-12}}</ref>

Unlike many shell commands that are implemented as separate [[application software|applications]], change directory is often built-in to the shell because it affects the [[State (computer science)|state]] of the shell whereas other commands modify system state outside the shell. If the command was implemented as a separate application, then the [[child process]] would need to modify state in the [[parent process]], but this is often prevented for safety. The command is built-in for most Unix shells ([[Bourne shell|Bourne]], [[tcsh]], [[Bash (Unix shell)|Bash]], etc.), Windows [[Command Prompt]] and [[PowerShell]], and MS-DOS [[COMMAND.COM]].

In a shell, the change directory command is typically implemented via a [[system call]] which on Unix and Unix-like systems is typically [[POSIX]] {{code|chdir()}} and on Windows is in the [[Windows API]]. 

The command is also provided in many programs other than shells. In the [[File Transfer Protocol]], the control stream command is {{code|CWD}}, but the functionality is available as {{code|cd}} in most command-line [[client (computing)|clients]] and some also provide {{code|lcd}} for changing the <u>l</u>ocal working directory vs. the remote setting. The [[numerical analysis|numerical computing]] environments [[MATLAB]] and [[GNU Octave]] include a
change directory command as <code>cd</code>.<ref>{{cite web|url=https://www.mathworks.com/help/matlab/ref/cd.html|title=Change current folder – MATLAB cd|website=www.mathworks.com}}</ref><ref>{{cite web|url=https://octave.sourceforge.io/octave/function/cd.html|title=Function Reference: cd|website=octave.sourceforge.io}}</ref>