<s>
Bash	B-Operating_System
is	O
a	O
Unix	B-Application
shell	I-Application
and	O
command	B-Language
language	I-Language
written	O
by	O
Brian	O
Fox	O
for	O
the	B-Application
GNU	I-Application
Project	I-Application
as	O
a	O
free	B-Application
software	I-Application
replacement	O
for	O
the	B-Device
Bourne	I-Device
shell	I-Device
.	O
</s>
<s>
First	O
released	O
in	O
1989	O
,	O
it	O
has	O
been	O
used	O
as	O
the	O
default	O
login	B-General_Concept
shell	O
for	O
most	O
Linux	B-Application
distributions	O
.	O
</s>
<s>
Bash	B-Operating_System
was	O
one	O
of	O
the	O
first	O
programs	O
Linus	O
Torvalds	O
ported	O
to	O
Linux	B-Application
,	O
alongside	O
GCC	B-Application
.	O
</s>
<s>
A	O
version	O
is	O
also	O
available	O
for	O
Windows	B-Operating_System
10	I-Operating_System
and	O
Windows	B-Application
11	I-Application
via	O
the	O
Windows	O
Subsystem	O
for	O
Linux	B-Application
.	O
</s>
<s>
It	O
is	O
also	O
the	O
default	O
user	O
shell	O
in	O
Solaris	B-Application
11	I-Application
.	O
</s>
<s>
Bash	B-Operating_System
was	O
also	O
the	O
default	O
shell	O
in	O
versions	O
of	O
Apple	B-Application
macOS	I-Application
from	O
10.3	O
(	O
originally	O
,	O
the	O
default	O
shell	O
was	O
tcsh	B-Language
)	O
to	O
10.15	O
(	O
macOS	B-Device
Catalina	I-Device
)	O
,	O
which	O
changed	O
the	O
default	O
shell	O
to	O
zsh	B-Application
,	O
although	O
Bash	B-Operating_System
remains	O
available	O
as	O
an	O
alternative	O
shell	O
.	O
</s>
<s>
Bash	B-Operating_System
is	O
a	O
command	B-Application
processor	O
that	O
typically	O
runs	O
in	O
a	O
text	B-Application
window	I-Application
where	O
the	O
user	O
types	O
commands	O
that	O
cause	O
actions	O
.	O
</s>
<s>
Bash	B-Operating_System
can	O
also	O
read	O
and	O
execute	O
commands	O
from	O
a	O
file	O
,	O
called	O
a	O
shell	B-Language
script	I-Language
.	O
</s>
<s>
Like	O
most	O
Unix	B-Application
shells	I-Application
,	O
it	O
supports	O
filename	O
globbing	B-Language
(	O
wildcard	O
matching	O
)	O
,	O
piping	B-Operating_System
,	O
here	O
documents	O
,	O
command	B-Device
substitution	I-Device
,	O
variables	O
,	O
and	O
control	O
structures	O
for	O
condition-testing	B-Language
and	O
iteration	B-Algorithm
.	O
</s>
<s>
The	O
keywords	O
,	O
syntax	O
,	O
dynamically	O
scoped	O
variables	O
and	O
other	O
basic	O
features	O
of	O
the	O
language	O
are	O
all	O
copied	O
from	O
sh	B-Device
.	O
</s>
<s>
Other	O
features	O
,	O
e.g.	O
,	O
history	O
,	O
are	O
copied	O
from	O
csh	B-Operating_System
and	O
ksh	B-Language
.	O
</s>
<s>
Bash	B-Operating_System
is	O
a	O
POSIX-compliant	O
shell	O
,	O
but	O
with	O
a	O
number	O
of	O
extensions	O
.	O
</s>
<s>
The	O
shell	O
's	O
name	O
is	O
an	O
acronym	O
for	O
Bourne	B-Operating_System
Again	I-Operating_System
Shell	I-Operating_System
,	O
a	O
pun	B-Application
on	O
the	O
name	O
of	O
the	B-Device
Bourne	I-Device
shell	I-Device
that	O
it	O
replaces	O
and	O
the	O
notion	O
of	O
being	O
"	O
born	O
again	O
"	O
.	O
</s>
<s>
A	O
security	O
hole	O
in	O
Bash	B-Operating_System
dating	O
from	O
version	O
1.03	O
(	O
August	O
1989	O
)	O
,	O
dubbed	O
Shellshock	O
,	O
was	O
discovered	O
in	O
early	O
September	O
2014	O
and	O
quickly	O
led	O
to	O
a	O
range	O
of	O
attacks	O
across	O
the	O
Internet	O
.	O
</s>
<s>
Brian	O
Fox	O
began	O
coding	B-General_Concept
Bash	B-Operating_System
on	O
January	O
10	O
,	O
1988	O
,	O
after	O
Richard	O
Stallman	O
became	O
dissatisfied	O
with	O
the	O
lack	O
of	O
progress	O
being	O
made	O
by	O
a	O
prior	O
developer	O
.	O
</s>
<s>
Stallman	O
and	O
the	B-Operating_System
Free	I-Operating_System
Software	I-Operating_System
Foundation	I-Operating_System
(	O
FSF	O
)	O
considered	O
a	O
free	O
shell	O
that	O
could	O
run	O
existing	O
shell	B-Language
scripts	I-Language
so	O
strategic	O
to	O
a	O
completely	O
free	O
system	O
built	O
from	O
BSD	O
and	O
GNU	B-Operating_System
code	O
that	O
this	O
was	O
one	O
of	O
the	O
few	O
projects	O
they	O
funded	O
themselves	O
,	O
with	O
Fox	O
undertaking	O
the	O
work	O
as	O
an	O
employee	O
of	O
FSF	O
.	O
</s>
<s>
Fox	O
released	O
Bash	B-Operating_System
as	O
a	O
beta	O
,	O
version	O
.99	O
,	O
on	O
June	O
8	O
,	O
1989	O
,	O
and	O
remained	O
the	O
primary	O
maintainer	O
until	O
sometime	O
between	O
mid-1992	O
and	O
mid-1994	O
,	O
when	O
he	O
was	O
laid	O
off	O
from	O
FSF	O
and	O
his	O
responsibility	O
was	O
transitioned	O
to	O
another	O
early	O
contributor	O
,	O
Chet	O
Ramey	O
.	O
</s>
<s>
Since	O
then	O
,	O
Bash	B-Operating_System
has	O
become	O
by	O
far	O
the	O
most	O
popular	O
shell	O
among	O
users	O
of	O
Linux	B-Application
,	O
becoming	O
the	O
default	O
interactive	O
shell	O
on	O
that	O
operating	O
system	O
's	O
various	O
distributions	O
(	O
although	O
Almquist	B-Operating_System
shell	I-Operating_System
may	O
be	O
the	O
default	O
scripting	O
shell	O
)	O
and	O
on	O
Apple	O
's	O
macOS	B-Application
releases	O
before	O
Catalina	B-Device
in	O
October	O
2019	O
.	O
</s>
<s>
Bash	B-Operating_System
has	O
also	O
been	O
ported	O
to	O
Microsoft	B-Application
Windows	I-Application
and	O
distributed	O
with	O
Cygwin	B-Language
and	O
MinGW	B-Application
,	O
to	O
DOS	B-Device
by	O
the	O
DJGPP	B-Application
project	O
,	O
to	O
Novell	B-Operating_System
NetWare	I-Operating_System
,	O
to	O
OpenVMS	B-Operating_System
by	O
the	O
GNV	O
project	O
,	O
to	O
ArcaOS	B-Device
,	O
and	O
to	O
Android	B-Application
via	O
various	O
terminal	B-Application
emulation	I-Application
applications	O
.	O
</s>
<s>
In	O
September	O
2014	O
,	O
Stéphane	O
Chazelas	O
,	O
a	O
Unix/Linux	O
specialist	O
,	O
discovered	O
a	O
security	O
bug	O
in	O
the	O
program	O
.	O
</s>
<s>
The	O
bug	O
was	O
regarded	O
as	O
severe	O
,	O
since	O
CGI	B-Language
scripts	I-Language
using	O
Bash	B-Operating_System
could	O
be	O
vulnerable	O
,	O
enabling	O
arbitrary	O
code	O
execution	O
.	O
</s>
<s>
The	O
bug	O
was	O
related	O
to	O
how	O
Bash	B-Operating_System
passes	O
function	O
definitions	O
to	O
subshells	O
through	O
environment	O
variables	O
.	O
</s>
<s>
The	O
Bash	B-Operating_System
command	B-Application
syntax	O
is	O
a	O
superset	O
of	O
the	B-Device
Bourne	I-Device
shell	I-Device
command	B-Application
syntax	O
.	O
</s>
<s>
Bash	B-Operating_System
supports	O
brace	O
expansion	O
,	O
command	B-Application
line	O
completion	O
(	O
Programmable	O
Completion	O
)	O
,	O
basic	O
debugging	O
and	O
signal	B-Operating_System
handling	I-Operating_System
(	O
using	O
trap	O
)	O
since	O
bash	B-Operating_System
2.05a	O
among	O
other	O
features	O
.	O
</s>
<s>
Bash	B-Operating_System
can	O
execute	O
the	O
vast	O
majority	O
of	O
Bourne	B-Device
shell	I-Device
scripts	O
without	O
modification	O
,	O
with	O
the	O
exception	O
of	O
Bourne	B-Device
shell	I-Device
scripts	O
stumbling	O
into	O
fringe	O
syntax	O
behavior	O
interpreted	O
differently	O
in	O
Bash	B-Operating_System
or	O
attempting	O
to	O
run	O
a	O
system	B-Application
command	I-Application
matching	O
a	O
newer	O
Bash	B-Operating_System
builtin	O
,	O
etc	O
.	O
</s>
<s>
Bash	B-Operating_System
command	B-Application
syntax	O
includes	O
ideas	O
drawn	O
from	O
the	O
KornShell	B-Language
(	O
ksh	B-Language
)	O
and	O
the	O
C	B-Operating_System
shell	I-Operating_System
(	O
csh	B-Operating_System
)	O
such	O
as	O
command	B-Application
line	O
editing	O
,	O
command	B-Application
history	I-Application
(	O
history	O
command	B-Application
)	O
,	O
the	O
directory	O
stack	O
,	O
the	O
$RANDOM	O
and	O
$PPID	O
variables	O
,	O
and	O
POSIX	O
command	B-Device
substitution	I-Device
syntax	O
$( 	O
…	O
)	O
.	O
</s>
<s>
When	O
a	O
user	O
presses	O
the	O
tab	O
key	O
within	O
an	O
interactive	O
command-shell	O
,	O
Bash	B-Operating_System
automatically	O
uses	O
command	B-Application
line	O
completion	O
,	O
since	O
beta	O
version	O
2.04	O
,	O
to	O
match	O
partly	O
typed	O
program	O
names	O
,	O
filenames	O
and	O
variable	O
names	O
.	O
</s>
<s>
The	O
Bash	B-Operating_System
command-line	O
completion	O
system	O
is	O
very	O
flexible	O
and	O
customizable	O
,	O
and	O
is	O
often	O
packaged	O
with	O
functions	O
that	O
complete	O
arguments	O
and	O
filenames	O
for	O
specific	O
programs	O
and	O
tasks	O
.	O
</s>
<s>
Bash	B-Operating_System
's	O
syntax	O
has	O
many	O
extensions	O
lacking	O
in	O
the	B-Device
Bourne	I-Device
shell	I-Device
.	O
</s>
<s>
Bash	B-Operating_System
can	O
perform	O
integer	O
calculations	O
(	O
"	O
arithmetic	O
evaluation	O
"	O
)	O
without	O
spawning	O
external	O
processes	O
.	O
</s>
<s>
It	O
uses	O
the	O
( ( 	O
…	O
)	O
)	O
command	B-Application
and	O
the	O
$( ( 	O
…	O
)	O
)	O
variable	O
syntax	O
for	O
this	O
purpose	O
.	O
</s>
<s>
Its	O
syntax	O
simplifies	O
I/O	B-Device
redirection	I-Device
.	O
</s>
<s>
This	O
is	O
simpler	O
to	O
type	O
than	O
the	B-Device
Bourne	I-Device
shell	I-Device
equivalent	O
'	O
command	B-Application
>	O
file	O
2>	O
&1	O
 '	O
.	O
</s>
<s>
Bash	B-Operating_System
supports	O
process	B-Device
substitution	I-Device
using	O
the	O
xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx1( command	O
)	O
syntax	O
,	O
which	O
substitutes	O
the	O
output	O
of	O
(	O
or	O
input	O
to	O
)	O
a	O
command	B-Application
where	O
a	O
filename	O
is	O
normally	O
used	O
.	O
</s>
<s>
(	O
This	O
is	O
implemented	O
through	O
/proc/fd/	O
unnamed	O
pipes	B-Operating_System
on	O
systems	O
that	O
support	O
that	O
,	O
or	O
via	O
temporary	O
named	B-Operating_System
pipes	I-Operating_System
where	O
necessary	O
)	O
.	O
</s>
<s>
When	O
using	O
the	O
'	O
function	O
 '	O
keyword	O
,	O
Bash	B-Operating_System
function	O
declarations	O
are	O
not	O
compatible	O
with	O
Bourne/Korn/POSIX	O
scripts	O
(	O
the	O
KornShell	B-Language
has	O
the	O
same	O
problem	O
when	O
using	O
'	O
function	O
 '	O
)	O
,	O
but	O
Bash	B-Operating_System
accepts	O
the	O
same	O
function	O
declaration	O
syntax	O
as	O
the	O
Bourne	O
and	O
Korn	B-Language
shells	I-Language
,	O
and	O
is	O
POSIX-conformant	O
.	O
</s>
<s>
Because	O
of	O
these	O
and	O
other	O
differences	O
,	O
Bash	B-Operating_System
shell	I-Operating_System
scripts	O
are	O
rarely	O
runnable	O
under	O
the	O
Bourne	O
or	O
Korn	B-Language
shell	I-Language
interpreters	O
unless	O
deliberately	O
written	O
with	O
that	O
compatibility	O
in	O
mind	O
,	O
which	O
is	O
becoming	O
less	O
common	O
as	O
Linux	B-Application
becomes	O
more	O
widespread	O
.	O
</s>
<s>
But	O
in	O
POSIX	O
mode	O
,	O
Bash	B-Operating_System
conforms	O
with	O
POSIX	O
more	O
closely	O
.	O
</s>
<s>
Bash	B-Operating_System
supports	O
here	O
documents	O
.	O
</s>
<s>
Since	O
version	O
2.05b	O
Bash	B-Operating_System
can	O
redirect	O
standard	O
input	O
(	O
stdin	O
)	O
from	O
a	O
"	O
here	O
string	O
"	O
using	O
the	O
<<<	O
operator	O
.	O
</s>
<s>
Bash	B-Operating_System
3.0	O
supports	O
in-process	O
regular	B-Language
expression	I-Language
matching	O
using	O
a	O
syntax	O
reminiscent	O
of	O
Perl	B-Language
.	O
</s>
<s>
In	O
February	O
2009	O
,	O
Bash	B-Operating_System
4.0	O
introduced	O
support	O
for	O
associative	B-Application
arrays	I-Application
.	O
</s>
<s>
Associative	B-Application
array	I-Application
indices	O
are	O
strings	O
,	O
in	O
a	O
manner	O
similar	O
to	O
AWK	B-Application
or	O
Tcl	B-Operating_System
.	O
</s>
<s>
Bash	B-Operating_System
4	O
also	O
switches	O
its	O
license	O
to	O
GPL-3.0-or-later	O
;	O
some	O
users	O
suspect	O
this	O
licensing	O
change	O
is	O
why	O
MacOS	B-Application
continues	O
to	O
use	O
older	O
versions	O
.	O
</s>
<s>
Apple	O
finally	O
stopped	O
using	O
Bash	B-Operating_System
in	O
their	O
operating	O
systems	O
as	O
default	O
shell	O
with	O
the	O
release	O
of	O
MacOS	B-Device
Catalina	I-Device
in	O
2019	O
.	O
</s>
<s>
Brace	O
expansion	O
,	O
also	O
called	O
alternation	O
,	O
is	O
a	O
feature	O
copied	O
from	O
the	O
C	B-Operating_System
shell	I-Operating_System
.	O
</s>
<s>
Users	O
should	O
not	O
use	O
brace	O
expansions	O
in	O
portable	O
shell	B-Language
scripts	I-Language
,	O
because	O
the	B-Device
Bourne	I-Device
shell	I-Device
does	O
not	O
produce	O
the	O
same	O
output	O
.	O
</s>
<s>
Newer	O
versions	O
of	O
Bash	B-Operating_System
allow	O
a	O
third	O
integer	O
to	O
specify	O
the	O
increment	O
.	O
</s>
<s>
When	O
Bash	B-Operating_System
starts	O
,	O
it	O
executes	O
the	O
commands	O
in	O
a	O
variety	O
of	O
dot	O
files	O
.	O
</s>
<s>
Unlike	O
Bash	B-Operating_System
shell	I-Operating_System
scripts	O
,	O
dot	O
files	O
do	O
not	O
typically	O
have	O
execute	O
permission	O
enabled	O
nor	O
an	O
interpreter	B-Operating_System
directive	I-Operating_System
like	O
#	O
!	O
/bin/bash	B-Operating_System
.	O
</s>
<s>
The	O
skeleton	O
~	O
/.bash_profile	O
below	O
is	O
compatible	O
with	O
the	B-Device
Bourne	I-Device
shell	I-Device
and	O
gives	O
semantics	O
similar	O
to	O
csh	B-Operating_System
for	O
the	O
~	O
/.bashrc	O
and	O
~	O
/.bash_login	O
.	O
</s>
<s>
Some	O
versions	O
of	O
Unix	B-Application
and	O
Linux	B-Application
contain	O
Bash	B-Operating_System
system	O
startup	O
scripts	O
,	O
generally	O
under	O
the	O
/etc	O
directories	O
.	O
</s>
<s>
Bash	B-Operating_System
calls	O
these	O
as	O
part	O
of	O
its	O
standard	O
initialization	O
,	O
but	O
other	O
startup	O
files	O
can	O
read	O
them	O
in	O
a	O
different	O
order	O
than	O
the	O
documented	O
Bash	B-Operating_System
startup	O
sequence	O
.	O
</s>
<s>
The	O
startup	O
scripts	O
that	O
launch	O
the	O
X	B-Operating_System
window	I-Operating_System
system	I-Operating_System
may	O
also	O
do	O
surprising	O
things	O
with	O
the	O
user	O
's	O
Bash	B-Operating_System
startup	O
scripts	O
in	O
an	O
attempt	O
to	O
set	O
up	O
user-environment	O
variables	O
before	O
launching	O
the	O
window	B-Application
manager	I-Application
.	O
</s>
<s>
These	O
issues	O
can	O
often	O
be	O
addressed	O
using	O
a	O
~	O
/.xsession	O
or	O
~	O
/.xprofile	O
file	O
to	O
read	O
the	O
~	O
/.profile	O
—	O
which	O
provides	O
the	O
environment	O
variables	O
that	O
Bash	B-Operating_System
shell	I-Operating_System
windows	O
spawned	O
from	O
the	O
window	B-Application
manager	I-Application
need	O
,	O
such	O
as	O
xterm	B-Language
or	O
Gnome	B-Language
Terminal	I-Language
.	O
</s>
<s>
Invoking	O
Bash	B-Operating_System
with	O
the	O
--posix	O
option	O
or	O
stating	O
set	O
-o	O
posix	O
in	O
a	O
script	O
causes	O
Bash	B-Operating_System
to	O
conform	O
very	O
closely	O
to	O
the	O
POSIX	O
1003.2	O
standard	O
.	O
</s>
<s>
Bash	B-Operating_System
shell	I-Operating_System
scripts	O
intended	O
for	O
portability	O
should	O
take	O
into	O
account	O
at	O
least	O
the	O
POSIX	O
shell	O
standard	O
.	O
</s>
<s>
Some	O
bash	B-Operating_System
features	O
not	O
found	O
in	O
POSIX	O
are	O
:	O
</s>
<s>
The	O
list	O
varies	O
depending	O
on	O
the	O
actual	O
target	O
shell	O
:	O
Debian	O
's	O
policy	O
allows	O
some	O
extensions	O
in	O
their	O
scripts	O
(	O
as	O
they	O
are	O
in	O
the	O
dash	O
shell	O
)	O
,	O
while	O
a	O
script	O
intending	O
to	O
support	O
pre-POSIX	O
Bourne	B-Device
shells	I-Device
,	O
like	O
autoconf	B-Application
's	O
,	O
are	O
even	O
more	O
limited	O
in	O
the	O
features	O
they	O
can	O
use	O
.	O
</s>
<s>
Bash	B-Operating_System
uses	O
readline	B-Application
to	O
provide	O
keyboard	O
shortcuts	O
for	O
command	B-Application
line	O
editing	O
using	O
the	O
default	O
(	O
Emacs	B-Application
)	O
key	O
bindings	O
.	O
</s>
<s>
The	O
Bash	B-Operating_System
shell	I-Operating_System
has	O
two	O
modes	O
of	O
execution	O
for	O
commands	O
:	O
batch	B-Device
,	O
and	O
concurrent	O
mode	O
.	O
</s>
<s>
To	O
execute	O
commands	O
in	O
batch	B-Device
(	O
i.e.	O
,	O
in	O
sequence	O
)	O
they	O
must	O
be	O
separated	O
by	O
the	O
character	O
"	O
;	O
"	O
,	O
or	O
on	O
separate	O
lines	O
:	O
</s>
<s>
A	O
background	B-Operating_System
execution	I-Operating_System
of	O
command1	O
can	O
occur	O
using	O
(	O
symbol	O
&	O
)	O
at	O
the	O
end	O
of	O
an	O
execution	O
command	B-Application
,	O
and	O
process	O
will	O
be	O
executed	O
in	O
background	O
returning	O
immediately	O
control	O
to	O
the	O
shell	O
and	O
allowing	O
continued	O
execution	O
of	O
commands	O
.	O
</s>
<s>
Or	O
to	O
have	O
a	O
concurrent	O
execution	O
of	O
two	O
command1	O
and	O
command2	O
,	O
they	O
must	O
be	O
executed	O
in	O
the	O
Bash	B-Operating_System
shell	I-Operating_System
in	O
the	O
following	O
way	O
:	O
</s>
<s>
A	O
process	O
can	O
be	O
stopped	O
and	O
control	O
returned	O
to	O
bash	B-Operating_System
by	O
typing	O
while	O
the	O
process	O
is	O
running	O
in	O
the	O
foreground	O
.	O
</s>
<s>
The	O
text	O
"	O
Running	O
"	O
and	O
"	O
Stopped	O
"	O
refer	O
to	O
the	O
process	B-Operating_System
state	I-Operating_System
.	O
</s>
<s>
The	O
last	O
string	O
is	O
the	O
command	B-Application
that	O
started	O
the	O
process	O
.	O
</s>
<s>
The	O
fg	O
command	B-Application
brings	O
a	O
process	O
to	O
the	O
foreground	O
,	O
while	O
bg	O
sets	O
a	O
stopped	O
process	O
running	O
in	O
the	O
background	O
.	O
</s>
<s>
The	O
kill	O
command	B-Application
can	O
be	O
used	O
to	O
end	O
a	O
process	O
prematurely	O
,	O
by	O
sending	O
it	O
a	O
signal	B-Operating_System
.	O
</s>
<s>
Bash	B-Operating_System
supplies	O
"	O
conditional	B-Language
execution	O
"	O
command	B-Application
separators	O
that	O
make	O
execution	O
of	O
a	O
command	B-Application
contingent	O
on	O
the	O
exit	B-Operating_System
code	I-Operating_System
set	O
by	O
a	O
precedent	O
command	B-Application
.	O
</s>
<s>
Where	O
./do_something	O
is	O
only	O
executed	O
if	O
the	O
cd	O
(	O
change	O
directory	O
)	O
command	B-Application
was	O
"	O
successful	O
"	O
(	O
returned	O
an	O
exit	B-Operating_System
status	I-Operating_System
of	O
zero	O
)	O
and	O
the	O
echo	O
command	B-Application
would	O
only	O
be	O
executed	O
if	O
either	O
the	O
cd	O
or	O
the	O
./do_something	O
command	B-Application
return	O
an	O
"	O
error	O
"	O
(	O
non-zero	O
exit	B-Operating_System
status	I-Operating_System
)	O
.	O
</s>
<s>
For	O
all	O
commands	O
the	O
exit	B-Operating_System
status	I-Operating_System
is	O
stored	O
in	O
the	O
special	O
variable	O
$	O
?	O
.	O
</s>
<s>
Bash	B-Operating_System
also	O
supports	O
and	O
forms	O
of	O
conditional	B-Language
command	B-Application
evaluation	O
.	O
</s>
<s>
An	O
external	O
command	B-Application
called	O
bashbug	O
reports	O
Bash	B-Operating_System
shell	I-Operating_System
bugs	O
.	O
</s>
<s>
When	O
the	O
command	B-Application
is	O
invoked	O
,	O
it	O
brings	O
up	O
the	O
user	O
's	O
default	O
editor	O
with	O
a	O
form	O
to	O
fill	O
in	O
.	O
</s>
<s>
The	O
form	O
is	O
mailed	O
to	O
the	O
Bash	B-Operating_System
maintainers	O
(	O
or	O
optionally	O
to	O
other	O
email	O
addresses	O
)	O
.	O
</s>
<s>
Bash	B-Operating_System
supports	O
programmable	O
completion	O
via	O
built-in	O
complete	O
,	O
,	O
and	O
compgen	O
commands	O
.	O
</s>
<s>
The	O
complete	O
and	O
two	O
commands	O
specify	O
how	O
arguments	O
of	O
some	O
available	O
commands	O
or	O
options	O
are	O
going	O
to	O
be	O
listed	O
in	O
the	O
readline	B-Application
input	O
.	O
</s>
<s>
As	O
of	O
version	O
5.1	O
completion	O
of	O
the	O
command	B-Application
or	O
the	O
option	O
is	O
usually	O
activated	O
by	O
the	O
keystroke	O
after	O
typing	O
its	O
name	O
.	O
</s>
