<s>
fish	O
is	O
a	O
Unix	B-Application
shell	I-Application
with	O
a	O
focus	O
on	O
interactivity	O
and	O
usability	O
.	O
</s>
<s>
Fish	O
is	O
considered	O
an	O
exotic	O
shell	B-Operating_System
since	O
it	O
does	O
not	O
rigorously	O
adhere	O
to	O
POSIX	O
shell	B-Operating_System
standards	O
,	O
at	O
the	O
discretion	O
of	O
the	O
maintainers	O
.	O
</s>
<s>
Fish	O
has	O
"	O
search	B-Application
as	I-Application
you	I-Application
type	I-Application
"	O
automatic	O
suggestions	O
based	O
on	O
history	O
and	O
current	O
directory	O
.	O
</s>
<s>
Tab-completion	O
is	O
feature-rich	O
,	O
expanding	O
file	O
paths	O
(	O
with	O
wildcards	B-Algorithm
and	O
brace	O
expansion	O
)	O
,	O
variables	O
,	O
and	O
many	O
command	O
specific	O
completions	O
.	O
</s>
<s>
Command-specific	O
completions	O
,	O
including	O
options	O
with	O
descriptions	O
,	O
can	O
to	O
some	O
extent	O
be	O
generated	O
from	O
the	O
commands	O
 '	O
man	B-Protocol
pages	I-Protocol
.	O
</s>
<s>
A	O
special	O
help	O
command	O
gives	O
access	O
to	O
all	O
the	O
fish	O
documentation	O
in	O
the	O
user	O
's	O
web	B-Application
browser	I-Application
.	O
</s>
<s>
The	O
syntax	O
resembles	O
a	O
POSIX	O
compatible	O
shell	B-Operating_System
(	O
such	O
as	O
Bash	O
)	O
,	O
but	O
deviates	O
in	O
important	O
ways	O
where	O
the	O
creators	O
believe	O
the	O
POSIX	O
shell	B-Operating_System
was	O
badly	O
designed	O
.	O
</s>
<s>
Some	O
language	O
constructs	O
,	O
like	O
pipelines	B-Operating_System
,	O
functions	O
and	O
loops	O
,	O
have	O
been	O
implemented	O
using	O
so	O
called	O
subshells	O
in	O
other	O
shell	B-Operating_System
languages	O
.	O
</s>
<s>
Subshells	O
are	O
child	O
programs	O
that	O
run	O
a	O
few	O
commands	O
for	O
the	O
shell	B-Operating_System
and	O
then	O
exit	O
.	O
</s>
<s>
This	O
implementation	O
detail	O
typically	O
has	O
the	O
side	O
effect	O
that	O
any	O
state	O
changes	O
made	O
in	O
the	O
subshell	O
,	O
such	O
as	O
variable	O
assignments	O
,	O
do	O
not	O
propagate	O
to	O
the	O
main	O
shell	B-Operating_System
.	O
</s>
<s>
Fish	O
has	O
a	O
feature	O
known	O
as	O
universal	O
variables	O
,	O
which	O
allow	O
a	O
user	O
to	O
permanently	O
assign	O
a	O
value	O
to	O
a	O
variable	O
across	O
all	O
the	O
user	O
's	O
running	O
fish	B-Language
shells	I-Language
.	O
</s>
<s>
Support	O
for	O
the	O
X	B-Operating_System
clipboard	O
.	O
</s>
<s>
Smart	O
terminal	B-General_Concept
handling	O
based	O
on	O
terminfo	B-Device
.	O
</s>
<s>
Searchable	O
command	B-Application
history	I-Application
.	O
</s>
<s>
${var[*]}	O
Identified	O
as	O
a	O
primary	O
cause	O
of	O
bugs	O
in	O
posix	O
compatible	O
shell	B-Operating_System
languages	O
variable	O
expansion:scalar	O
"	O
$var	O
"	O
Every	O
variable	O
is	O
an	O
array	O
variable	O
expansion:array	O
"${var[@]}"	O
$var	O
Quoting	O
not	O
necessary	O
to	O
suppress	O
word	O
splitting	O
and	O
glob	B-Language
interpretation	O
.	O
</s>
<s>
LANG	O
=	O
C.UTF-8	O
python3	O
env	O
LANG	O
=	O
C.UTF-8	O
python3	O
env	O
LANG	O
=	O
C.UTF-8	O
python3	O
works	O
in	O
any	O
shell	B-Operating_System
,	O
as	O
env	O
is	O
a	O
standalone	O
program	O
.	O
</s>
<s>
$( ( 	O
10/3	O
)	O
)	O
math	O
'	O
10/3	O
'	O
expr	O
10	O
/	O
3	O
works	O
in	O
any	O
shell	B-Operating_System
,	O
as	O
expr	O
is	O
a	O
standalone	O
program	O
.	O
</s>
