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$ help
$ help | less
$ help | grep read 

GNU bash, version 4.1.5(1)-release (x86_64-pc-linux-gnu)
These shell commands are defined internally. Type `help' to see this list.
Type `help name' to find out more about the function `name'.
Use `info bash' to find out more about the shell in general.
Use `man -k' or `info' to find out more about commands not in this list.
 
A star (*) next to a name means that the command is disabled.
 
 job_spec [&]              history [-c] [-d offset] [n] or hist>
 (( expression ))            if COMMANDS; then COMMANDS; [ elif C>
 . filename [arguments]         jobs [-lnprs] [jobspec ...] or jobs >
 :                    kill [-s sigspec | -n signum | -sigs>
 [ arg... ]               let arg [arg ...]
 [[ expression ]]            local [option] name[=value] ...
 alias [-p] [name[=value] ... ]     logout [n]
 bg [job_spec ...]            mapfile [-n count] [-O origin] [-s c>
 bind [-lpvsPVS] [-m keymap] [-f filen> popd [-n] [+N | -N]
 break [n]                printf [-v var] format [arguments]
 builtin [shell-builtin [arg ...]]    pushd [-n] [+N | -N | dir]
 caller [expr]              pwd [-LP]
 case WORD in [PATTERN [| PATTERN]...)> read [-ers] [-a array] [-d delim] [->
 cd [-L|-P] [dir]            readarray [-n count] [-O origin] [-s>
 command [-pVv] command [arg ...]    readonly [-af] [name[=value] ...] or>
 compgen [-abcdefgjksuv] [-o option] > return [n]
 complete [-abcdefgjksuv] [-pr] [-DE] > select NAME [in WORDS ... ;] do COMM>
 compopt [-o|+o option] [-DE] [name ..> set [--abefhkmnptuvxBCHP] [-o option>
 continue [n]              shift [n]
 coproc [NAME] command [redirections]  shopt [-pqsu] [-o] [optname ...]
 declare [-aAfFilrtux] [-p] [name[=val> source filename [arguments]
 dirs [-clpv] [+N] [-N]         suspend [-f]
 disown [-h] [-ar] [jobspec ...]     test [expr]
 echo [-neE] [arg ...]          time [-p] pipeline
 enable [-a] [-dnps] [-f filename] [na> times
 eval [arg ...]             trap [-lp] [[arg] signal_spec ...]
 exec [-cl] [-a name] [command [argume> true
 exit [n]                type [-afptP] name [name ...]
 export [-fn] [name[=value] ...] or ex> typeset [-aAfFilrtux] [-p] name[=val>
 false                  ulimit [-SHacdefilmnpqrstuvx] [limit>
 fc [-e ename] [-lnr] [first] [last] o> umask [-p] [-S] [mode]
 fg [job_spec]              unalias [-a] name [name ...]
 for NAME [in WORDS ... ] ; do COMMAND> unset [-f] [-v] [name ...]
 for (( exp1; exp2; exp3 )); do COMMAN> until COMMANDS; do COMMANDS; done
 function name { COMMANDS ; } or name > variables - Names and meanings of so>
 getopts optstring name [arg]      wait [id]
 hash [-lr] [-p pathname] [-dt] [name > while COMMANDS; do COMMANDS; done
 help [-dms] [pattern ...]        { COMMANDS ; }

compgen -b
compgen -b | more

help command
help read

$ help -d

help name 
help cd 
help fg 
help for 
help read 
help :

:: :
 Null command.
 
 No effect; the command does nothing.
 
 Exit Status:
 Always succeeds

type -a command-name-here 
type -a cd 
type -a uname 
type -a : 
type -a ls

type -a cd uname : ls uname

cd is a shell builtin
uname is /bin/uname
: is a shell builtin
ls is aliased to `ls --color=auto'
ls is /bin/ls
l is a function
l ()
{
 ls --color=auto
}

command -V ls 
command -V cd 
command -V foo