Error in setup script (which: command not found)

When I try to run the ISPConfig install script, I get an error when it checks for MTA. I am running CentOS 5.2 and have followed the entire "Perfect Server" tutorial, everything went OK as far as I can see, but when I try to install ISPConfig, it goes wrong. This is the error I get:

Code:

########## MAIL SERVER ##########

Checking for MTA...
./setup2: line 438: which: command not found
./setup2: line 438: which: command not found
ERROR: Your system configuration is not compatible with ISPConfig! The installation routine stops here!

This is the code itself:

Code:

while [ "$index" -lt "$element_count" ]
  do
    which ${array[$index]}
    if [ $? == 0 ]; then
      server=${array[$index]}
      echo OK
      let check=1
      break
    fi
    let "index = $index + 1"
  done

So it stops at the 'which' on the 3rd line of the above snippet. Does anybody have a clue why it goes wrong? Maybe I am missing a package?

 

Ah never mind, a simple yum install which did the trick Sorry to be wasting your time.