bash 本身内置了一些命令，所谓内置（内部）命令就是Bash本身就集成支持的命令，大约有60来个。

bash
:
.
[
alias
bg
bind
break
builtin
caller 
command
compgen
complete
compopt
continue
declare
dirs
disown
echo
enable
eval
exec
exit
export
false
fc
fg
getopts
hash
help
history
jobs
kill
let
local
logout
mapfile
popd
printf
pushd
pwd
read
readonly
return
set
shift
shopt
source
suspend
test
times
trap
true
type
typeset
ulimit
umask
unalias
unset
wait