$ type foo >/dev/null 2>&1 || { echo >&2 "I require foo but it's not installed.  Aborting."; exit 1; }

[root@new55 ~]#?type -a type?
type is a shell builtin
[root@new55 ~]#?help type?
type: type [-afptP] name [name ...]
??? For each NAME, indicate how it would be interpreted if used as a
??? command name.
??? If the -t option is used, `type' outputs a single word which is one of
??? `alias', `keyword', `function', `builtin', `file' or `', if NAME is an
??? alias, shell reserved word, shell function, shell builtin, disk file,
??? or unfound, respectively.
??? If the -p flag is used, `type' either returns the name of the disk
??? file that would be executed, or nothing if `type -t NAME' would not
??? return `file'.
??? If the -a flag is used, `type' displays all of the places that contain
??? an executable named `file'.? This includes aliases, builtins, and
??? functions, if and only if the -p flag is not also used.
??? The -f flag suppresses shell function lookup.
??? The -P flag forces a PATH search for each NAME, even if it is an alias,
??? builtin, or function, and returns the name of the disk file that would
??? be executed.
typeset: typeset [-afFirtx] [-p] name[=value] ...
??? Obsolete.? See `declare'.
[root@new55 ~]#

[root@new55 ~]#?type -a cd?
cd is a shell builtin
[root@new55 ~]#?type -a pwd?
pwd is a shell builtin
pwd is /bin/pwd
[root@new55 ~]#?type -a time?
time is a shell keyword
time is /usr/bin/time
[root@new55 ~]#?type -a date?
date is /bin/date
[root@new55 ~]#?type -a which?
which is aliased to `alias | /usr/bin/which --tty-only --read-alias --show-dot --show-tilde'
which is /usr/bin/which
[root@new55 ~]#?type -a whereis?
whereis is /usr/bin/whereis
[root@new55 ~]#?type -a whatis?
whatis is /usr/bin/whatis
[root@new55 ~]#?type -a function?
function is a shell keyword
[root@new55 ~]#?type -a ls?
ls is aliased to `ls --color=tty'
ls is /bin/ls
[root@new55 ~]#?type -a ll?
ll is aliased to `ls -l --color=tty'
[root@new55 ~]#?type -a echo?
echo is a shell builtin
echo is /bin/echo
[root@new55 ~]#?type -a bulitin?
-bash: type: bulitin: not found
[root@new55 ~]#?type -a builtin?
builtin is a shell builtin
[root@new55 ~]#?type -a keyword?
-bash: type: keyword: not found
[root@new55 ~]#?type -a command?
command is a shell builtin
[root@new55 ~]#?type -a alias?
alias is a shell builtin
[root@new55 ~]#?type -a grep?
grep is /bin/grep