Editing Echo (command)

{{Short description|Shell command for writing to standard output}}
{{otheruses|Echo (disambiguation)}}
{{lowercase}}
{{Infobox software
| name                   = echo
| logo                   = 
| screenshot             = Sleepunix.png
| screenshot size        = 
| caption                = The {{code|echo}} command on [[Unix]]
| author                 = [[Douglas McIlroy]]<br />([[AT&T Bell Laboratories]])
| developer              = Various [[open-source software|open-source]] and [[commercial software|commercial]] developers
| released               = 
| latest release version = 
| latest release date    = 
| operating system       = [[Multics]], [[Unix]], [[Unix-like]], [[V (operating system)|V]], [[Plan 9 from Bell Labs|Plan 9]], [[Inferno (operating system)|Inferno]], [[FLEX (operating system)|FLEX]], [[TRIPOS]], [[AmigaDOS]], [[Z80-RIO]], [[OS-9]], [[DOS]], [[MSX-DOS]], [[Panos (operating system)|Panos]], [[FlexOS]], [[SISNE plus]], [[OS/2]], [[Microsoft Windows|Windows]], [[ReactOS]], [[HP Multi-Programming Executive|MPE/iX]], [[KolibriOS]], [[SymbOS]]
| platform               = [[Cross-platform]]
| genre                  = [[Command (computing)|Command]]
| license                = 
| website                = 
}}
'''<code>echo</code>''' is [[shell (computing)|shell]] [[command (computing)|command]] that writes input text to [[standard output]]. It is available in many [[operating system]] and [[shell (computing)|shells]]. It is often used in a [[shell script]] to [[Logging (computing)|log]] status, provide feedback to the user and for [[debugging]]. For an interactive session, output by default displays on the [[computer terminal|terminal]] screen, but output can be [[Redirection (computing)|re-directed]] to a [[computer file|file]] or [[Pipeline (Unix)|piped]] to another process.<ref name="rugheimer-spanik-amigados" />

Many shells implement <code>echo</code> as a [[shell builtin|builtin command]] rather than an external [[application software|application]] as are many other commands.

Multiple, incompatible implementations of <code>echo</code> exist in different shells. Some expand escape sequences by default; some do not; some accept options; some do not. The [[POSIX]] specification<ref>{{man|cu|echo|SUS|write arguments to standard output}}</ref> leaves the behavior unspecified if the first argument is <code>-n</code> or any argument contains backslash characters while the Unix specification (XSI option in POSIX) mandates the expansion of some sequences and does not allow any option processing. In practice, many <code>echo</code> implementations are not compliant in the default environment. Because of these variations, <code>echo</code> is considered a non-portable command<ref name="echo limitations" /> and the [[printf (Unix)|<code>printf</code> command]] (introduced in Ninth Edition Unix) is preferred instead.

==Implementations==
The command is available the following shells or at least one shell of a listed operating system:
* [[Unix]] and [[Unix-like]] shells
* [[Windows]]<ref name="windows-commands" />
* [[Multics]]<ref name="multics" />
* [[OS/2]]<ref name="jatomes" />
* [[DOS]]
* [[Technical Systems Consultants|TSC]] [[FLEX (operating system)|FLEX]]<ref name="flexusergroup" />
* [[MetaComCo]] [[TRIPOS]]<ref name="tripos" />
* [[Zilog]] [[Z80-RIO]]<ref name="z80 user guide" />
* [[OS-9]]<ref name="os-9 guru" />
* [[Panos (operating system)|Panos]]<ref name="computinghistory" />
* [[FlexOS]]<ref name="flexos user guide" />
* [[ReactOS]]<ref name="reactos" />
* [[HP Multi-Programming Executive|MPE/iX]]<ref name="teamnaconsulting" />
* [[KolibriOS]]<ref name="kolibrios" />
* [[SymbOS]]
* [[Unified Extensible Firmware Interface|EFI shell]].<ref name="EFI-Shells-and-Scripting" />

==History==
<code>echo</code> began within [[Multics]]. After it was programmed in [[C (programming language)|C]] by [[Douglas McIlroy|Doug McIlroy]] as a "finger exercise" and proved to be useful, it became part of [[Version 2 Unix]]. <code>echo -n</code> in [[Version 7 Unix|Version 7]] replaced <code>prompt</code>, (which behaved like <code>echo</code> but without terminating its output with a line delimiter).<ref name="reader" />

On [[PWB/UNIX]] and later [[Unix System III]], <code>echo</code> started expanding [[Escape sequences in C|C escape sequences]] such as <code>\n</code> with the notable difference that octal escape sequences were expressed as <code>\0ooo</code> instead of <code>\ooo</code> in C.<ref name="mascheck-echo" />

[[Research Unix|Eighth Edition Unix]] <code>echo</code> only did the escape expansion when passed a <code>-e</code> option,<ref name="man echo" /> and that behaviour was copied by a few other implementations such as the builtin <code>echo</code> command of [[Bash (Unix shell)|Bash]] or [[zsh]] and GNU <code>echo</code>.

On [[MS-DOS]], the command is available in versions 2 and later.<ref name="RUNNINGMSDOS" />

==Examples==
<syntaxhighlight lang="doscon">
C:\>echo Hello world
Hello world
</syntaxhighlight>

Using [[ANSI escape code]] ''SGR'' sequences, compatible terminals can print out colored text.

Using a [[UNIX System III]]-style implementation:

<syntaxhighlight lang="bash">
BGRED=`echo "\033[41m"`
FGBLUE=`echo "\033[35m"`
BGGREEN=`echo "\033[42m"`
NORMAL=`echo "\033[m"`
</syntaxhighlight>

Or a Unix Version 8-style implementation (such as Bash when not in Unix-conformance mode):

<syntaxhighlight lang="bash">
BGRED=`echo -e "\033[41m"`
FGBLUE=`echo -e "\033[35m"`
BGGREEN=`echo -e "\033[42m"`
NORMAL=`echo -e "\033[m"`
</syntaxhighlight>

and after:

<syntaxhighlight lang="bash">
echo "${FGBLUE} Text in blue ${NORMAL}"
echo "Text normal"
echo "${BGRED} Background in red"
echo "${BGGREEN} Background in Green and back to Normal ${NORMAL}"
</syntaxhighlight>

Portably with <code>printf</code>:

<syntaxhighlight lang="bash">
BGRED=`printf '\33[41m'`
NORMAL=`printf '\33[m'`
printf '%s\n' "${BGRED}Text on red background${NORMAL}"
</syntaxhighlight>

==See also==
* {{Annotated link|List of DOS commands}}
* {{Annotated link|List of POSIX commands}}

==References==
{{Reflist|refs=
<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>

<ref name="mascheck-echo">{{cite web|last1=Mascheck|first1=Sven|title=echo and printf behaviour|url=http://www.in-ulm.de/~mascheck/various/echo+printf/|access-date=24 July 2016}}</ref>

<ref name="man echo">{{cite web|title=8th Edition Unix echo man page|url=http://man.cat-v.org/unix_8th/1/echo|access-date=24 July 2016}}</ref>

<ref name="echo limitations">{{cite web|title=Autoconf documentation on echo portability|url=https://www.gnu.org/software/autoconf/manual/autoconf-2.66/html_node/Limitations-of-Builtins.html#echo|publisher=Free Software Foundation|access-date=24 July 2016}}</ref>

<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>

<ref name="jatomes">{{Cite web |url=http://www.jatomes.com/Help/Os2Bat.php |title=OS/2 Batch File Commands |archive-url=https://web.archive.org/web/20190414130026/http://www.jatomes.com/Help/Os2Bat.php |archive-date=2019-04-14 |url-status=dead}}</ref>

<ref name="flexos user guide">{{Cite web |url=http://www.bitsavers.org/pdf/digitalResearch/flexos/1073-2003_FlexOS_Users_Guide_V1.3_Nov86.pdf |title=FlexOS™ User's Guide |archive-url=https://web.archive.org/web/20180914132130/http://www.bitsavers.org/pdf/digitalResearch/flexos/1073-2003_FlexOS_Users_Guide_V1.3_Nov86.pdf |archive-date=2018-09-14 |url-status=dead}}</ref>

<ref name="tripos">{{cite web |url=https://www.pagetable.com/docs/amigados_tripos/tripos_manuals.pdf |title= Manual |website=www.pagetable.com|access-date=2020-09-12}}</ref>

<ref name="z80 user guide">{{Cite web |url=https://www.z80cpu.eu/mirrors/oldcomputers.dyndns.org/public/pub/rechner/zilog/zds/z80-rio_os_userman.pdf |title=Z80-RIO OPERATING SYSTEM USER'S MANUAL}}</ref>

<ref name="os-9 guru">{{cite book|author=Paul S. Dayan|year=1992|title=The OS-9 Guru - 1 : The Facts|publisher=Galactic Industrial Limited|isbn=0-9519228-0-7}}</ref>

<ref name="reader">{{cite tech report |first1=M. D. |last1=McIlroy |author-link1=Doug McIlroy |year=1987 |url=http://www.cs.dartmouth.edu/~doug/reader.pdf |title=A Research Unix reader: annotated excerpts from the Programmer's Manual, 1971–1986 |series=CSTR |number=139 |institution=Bell Labs}}</ref>

<ref name="rugheimer-spanik-amigados">{{Cite book|url=https://archive.org/details/1988-rugheimer-spanik-amigados-quick-reference|title=AmigaDOS quick reference|first1=Hannes|last1=Rügheimer|first2=Christian|last2=Spanik|date=September 12, 1988|publisher=Grand Rapids, Mi : Abacus|isbn=9781557550491|via=Internet Archive}}</ref>

<ref name="computinghistory">{{Cite web|url=http://chrisacorns.computinghistory.org.uk/Panos.html#CL|title=Chris's Acorns: Panos|website=chrisacorns.computinghistory.org.uk}}</ref>

<ref name="windows-commands">{{Cite web|url=https://docs.microsoft.com/en-us/windows-server/administration/windows-commands/echo|title=echo|website=docs.microsoft.com|date=2 October 2023 }}</ref>

<ref name="flexusergroup">{{Cite web|url=http://www.flexusergroup.com/flexusergroup/pdfs/swflexum.pdf|title=FLEX 9.0 User's Manual}}</ref>

<ref name="teamnaconsulting">{{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>

<ref name="reactos">{{Cite web|url=https://github.com/reactos/reactos|title=reactos/reactos|website=GitHub|date=3 January 2022}}</ref>

<ref name="kolibrios">{{Cite web|url=http://wiki.kolibrios.org/wiki/Shell|title=Shell - KolibriOS wiki|website=wiki.kolibrios.org}}</ref>

<ref name="multics">{{Cite web|url=https://www.multicians.org/multics-commands.html|title=Multics Commands|website=www.multicians.org}}</ref>
}}

==Further reading==
*{{Cite book|author-last=Wolverton|author-first=Van|title=MS-DOS Commands: Microsoft Quick Reference, 4th Revised edition|date=1990|publisher=[[Microsoft Press]]|isbn=978-1556152894}}
*{{Cite book|author1=Kathy Ivens|author2=Brian Proffit|year=1993|title=OS/2 Inside & Out|publisher=[[Osborne McGraw-Hill]]|isbn=978-0078818714}}
*{{Cite book|first=Æleen|last=Frisch|year=2001|title=Windows 2000 Commands Pocket Reference|publisher=[[O'Reilly Media|O'Reilly]]|isbn=978-0-596-00148-3}}

==External links==
{{Wikibooks|Guide to Windows Commands}}
{{Wikibooks|Guide to Unix|Commands}}
*{{man|cu|echo|SUS|write arguments to standard output}}
*{{man|1|echo|Plan 9}}
*{{man|1|echo|Inferno}}
*[https://technet.microsoft.com/en-us/library/bb490897.aspx Microsoft TechNet Echo article]

{{Unix commands}}
{{Plan 9 commands}}
{{Core Utilities commands}}
{{Windows commands}}

[[Category:Internal DOS commands]]
[[Category:MSX-DOS commands]]
[[Category:OS/2 commands]]
[[Category:ReactOS commands]]
[[Category:Windows commands]]
[[Category:Multics commands]]
[[Category:Standard Unix programs]]
[[Category:Unix SUS2008 utilities]]
[[Category:Plan 9 commands]]
[[Category:Inferno (operating system) commands]]
[[Category:IBM i Qshell commands]]