type - Writing shell scripts

I've started skimming through the lovely Writing shell scripts tutorial and even though I'm just in the beginning of it I've already learnt one very useful thing: the type program. With it you can find out "what type of command it is". This is useful because sometimes you want to know where some command is coming from. I'll let this example explain its usage:

peterbe@trillian:~ $ type jed
jed is /usr/bin/jed
peterbe@trillian:~ $ type cvs_commit 
cvs_commit is /home/peterbe/bin/cvs_commit
peterbe@trillian:~ $ type alias
alias is a shell builtin
peterbe@trillian:~ $ type sjed
sjed is aliased to `sudo jed'

I'll read more of this after the weekend.