Challenge (Tina Wood)

'whatis commandname' - a command that returns the header line (and
section number) of the manual page for commandname.  You can then look up
the entirety of the manual page using 'man commandname'.  If >1 section
is given, specify the section you're interested in looking up using 'man
-s sectionnumber commandname'.

'man commandname' - a command that returns the reference manual page for
commandname.  'man -a commandname' returns all sections appended together
if >1 section exists.  'man -s sectionnumber commandname' allows you to
specify the section number you're interested in if >1 section exists. 
'xman' allows you to see a list of commands organized by section, and
search the man pages for the key word as the command name or in the
header line.

'apropos keyword' - a command that returns the command name, section
number, and header line of the manual page for every command whose header
line contains the keyword.  Apropos will find the desired keyword if it
is a substring of a larger word in the header line as well.


Use these tools to find a command to determine the type of a random file:
> whatis file
file            file (n)        - Manipulate file names and attributes
file            file (1)        - determine file type
file            file (1b)       - determine the type of a file by
examining its contents
file            file (1)        - determine file type
file            file (1b)       - determine the type of a file by
examining its contents

> apropos file | grep type | grep determine
(excerpt)
file            file (1)        - determine file type
file            file (1b)       - determine the type of a file by
examining its contents

'file filename' tests filename to identify its type, including directory,
character special, programming language, or empty file.


Try it on the files in the tarball:
> file mystery_file1
mystery_file1:  ELF 32-bit LSB dynamic lib 80386 Version 1, dynamically
linked, stripped

> file mystery_file2
mystery_file2:  ELF 32-bit LSB executable 80386 Version 1, dynamically
linked, stripped

> file mystery_file3
mystery_file3:  ELF 32-bit LSB core file 80386 Version 1, from 'Š'

Results:
mystery_file1 is an ELF DLL
mystery_file2 is an ELF executable
mystery_file3 is an ELF core file

Puzzler (Kevin Arhelger)

See file upi.sh.gz. There are a few improvements that could
be made... First of all, always write scripts for the Bourne shell unless you
need interactive features.  

Secondly, exit after printing the usage.  

Finally, although this is not a mistake, it is often more convenient to make
your scripts read in from standard input and output to standard output.  It's
almost always easier to deal with un-named pipes that using the named variety.

Other than that, great answer!