Editing Echo (command) (section)

{{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.