A traditional spell command will spellcheck one or more
files given on the command line (or stdin if there are no
files given on the command line), and misspelled words will
only be given once.

 The 'spell' script included in the ispell RPM will only
spellcheck standard input and will repeat misspelled words
as many times as they occur in the input.

Reproduction:
$ echo This spel command is awful at catchng spel mistakes
>/tmp/spelltest
$ spell </dev/null /tmp/spelltest
[no output]
$ spell </tmp/spelltest
spel
catchng
spel

 The simple fix appears to be to replace spell with the
following shell script:
	#!/bin/sh
	cat "$@" | ispell -l | sort -u

(This bug report is applicable to RedHat 6.1 unless the
behavior of 'ispell -l' has changed, which the manpage
claims it has not.)

 There is also no manpage for the spell command.