<s>
In	O
computing	O
,	O
echo	B-Application
is	O
a	O
command	B-Application
that	O
outputs	O
the	O
strings	O
that	O
are	O
passed	O
to	O
it	O
as	O
arguments	O
.	O
</s>
<s>
It	O
is	O
a	O
command	B-Application
available	O
in	O
various	O
operating	B-Operating_System
system	I-Operating_System
shells	I-Operating_System
and	O
typically	O
used	O
in	O
shell	B-Language
scripts	I-Language
and	O
batch	O
files	O
to	O
output	O
status	O
text	O
to	O
the	O
screen	O
or	O
a	O
computer	B-Operating_System
file	I-Operating_System
,	O
or	O
as	O
a	O
source	O
part	O
of	O
a	O
pipeline	B-Operating_System
.	O
</s>
<s>
The	O
command	B-Application
is	O
available	O
in	O
the	O
following	O
operating	B-General_Concept
systems	I-General_Concept
:	O
</s>
<s>
Many	O
shells	B-Operating_System
,	O
including	O
all	O
Bourne-like	O
(	O
such	O
as	O
Bash	B-Operating_System
or	O
zsh	B-Application
)	O
and	O
Csh-like	O
shells	B-Operating_System
as	O
well	O
as	O
COMMAND.COM	B-Operating_System
and	O
cmd.exe	B-Device
implement	O
echo	B-Application
as	O
a	O
builtin	O
command	B-Application
.	O
</s>
<s>
The	O
command	B-Application
is	O
also	O
available	O
in	O
the	O
EFI	B-Architecture
shell	I-Architecture
.	O
</s>
<s>
echo	B-Application
began	O
within	O
Multics	B-Application
.	O
</s>
<s>
After	O
it	O
was	O
programmed	O
in	O
C	B-Language
by	O
Doug	O
McIlroy	O
as	O
a	O
"	O
finger	O
exercise	O
"	O
and	O
proved	O
to	O
be	O
useful	O
,	O
it	O
became	O
part	O
of	O
Version	B-Operating_System
2	I-Operating_System
Unix	I-Operating_System
.	O
</s>
<s>
echo	B-Application
-n	O
in	O
Version	B-Operating_System
7	I-Operating_System
replaced	O
prompt	O
,	O
(	O
which	O
behaved	O
like	O
echo	B-Application
but	O
without	O
terminating	O
its	O
output	O
with	O
a	O
line	O
delimiter	O
)	O
.	O
</s>
<s>
On	O
PWB/UNIX	B-Operating_System
and	O
later	O
Unix	B-Operating_System
System	I-Operating_System
III	I-Operating_System
,	O
echo	B-Application
started	O
expanding	O
C	B-Language
escape	I-Language
sequences	I-Language
such	O
as	O
\n	O
with	O
the	O
notable	O
difference	O
that	O
octal	O
escape	O
sequences	O
were	O
expressed	O
as	O
\0ooo	O
instead	O
of	O
\ooo	O
in	O
C	B-Language
.	O
</s>
<s>
Eighth	B-Operating_System
Edition	I-Operating_System
Unix	I-Operating_System
echo	B-Application
only	O
did	O
the	O
escape	O
expansion	O
when	O
passed	O
a	O
-e	O
option	O
,	O
and	O
that	O
behaviour	O
was	O
copied	O
by	O
a	O
few	O
other	O
implementations	O
such	O
as	O
the	O
builtin	O
echo	B-Application
command	I-Application
of	O
Bash	B-Operating_System
or	O
zsh	B-Application
and	O
GNU	O
echo	B-Application
.	O
</s>
<s>
On	O
MS-DOS	B-Application
,	O
the	O
command	B-Application
is	O
available	O
in	O
versions	O
2	O
and	O
later	O
.	O
</s>
<s>
Nowadays	O
,	O
several	O
incompatible	O
implementations	O
of	O
echo	B-Application
exist	O
on	O
different	O
operating	B-General_Concept
systems	I-General_Concept
(	O
often	O
several	O
on	O
the	O
same	O
system	O
)	O
,	O
some	O
of	O
them	O
expanding	O
escape	O
sequences	O
by	O
default	O
,	O
some	O
of	O
them	O
not	O
,	O
some	O
of	O
them	O
accepting	O
options	O
(	O
the	O
list	O
of	O
which	O
varying	O
with	O
implementations	O
)	O
,	O
some	O
of	O
them	O
not	O
.	O
</s>
<s>
The	O
POSIX	O
specification	O
of	O
echo	B-Application
leaves	O
the	O
behaviour	O
unspecified	O
if	O
the	O
first	O
argument	O
is	O
-n	O
or	O
any	O
argument	O
contain	O
backslash	O
characters	O
while	O
the	O
Unix	B-Application
specification	O
(	O
XSI	O
option	O
in	O
POSIX	O
)	O
mandates	O
the	O
expansion	O
of	O
(	O
some	O
)	O
sequences	O
and	O
does	O
not	O
allow	O
any	O
option	O
processing	O
.	O
</s>
<s>
In	O
practice	O
,	O
many	O
echo	B-Application
implementations	O
are	O
not	O
compliant	O
in	O
the	O
default	O
environment	O
.	O
</s>
<s>
Because	O
of	O
these	O
variations	O
in	O
behaviour	O
,	O
echo	B-Application
is	O
considered	O
a	O
non-portable	O
command	B-Application
on	O
Unix-like	B-Operating_System
systems	I-Operating_System
and	O
the	O
printf	B-Device
command	B-Application
(	O
where	O
available	O
,	O
introduced	O
by	O
Ninth	O
Edition	O
Unix	B-Application
)	O
is	O
preferred	O
instead	O
.	O
</s>
<s>
Or	O
a	O
Unix	B-Application
Version	O
8-style	O
implementation	O
(	O
such	O
as	O
Bash	B-Operating_System
when	O
not	O
in	O
Unix-conformance	O
mode	O
)	O
:	O
</s>
<s>
Portably	O
with	O
printf	B-Device
:	O
</s>
