#!/bin/sh
# VALIDATOR - Checks to ensure that all environment variables are valid
#   looks at SHELL, HOME, PATH, EDITOR, MAIL, and PAGER

errors=0

in_path()
{
  # given a command and the PATH, try to find the command. Returns
  # 1 if found, 0 if not.  Note that this temporarily modifies the
  # the IFS input field seperator, but restores it upon completion.
  cmd=$1    path=$2    retval=0

  oldIFS=$IFS; IFS=":"

  for directory in $path 
  do
    if [ -x $directory/$cmd ] ; then
      retval=1      # if we're here, we found $cmd in $directory
    fi
  done
  IFS=$oldIFS
  return $retval
}

validate()
{
  varname=$1    varvalue=$2
  
  if [ ! -z $varvalue ] ; then
    if [ "${varvalue%${varvalue#?}}" = "/" ] ; then
      if [ ! -x $varvalue ] ; then
        echo "** $varname set to $varvalue, but I cannot find executable."
        errors=$(( $errors + 1 ))
      fi
    else
      if in_path $varvalue $PATH ; then 
        echo "** $varname set to $varvalue, but I cannot find it in PATH."
        errors=$(( $errors + 1 ))
      fi
    fi 
  fi
}

####### Beginning of actual shell script #######

if [ ! -x ${SHELL:?"Cannot proceed without SHELL being defined."} ] ; then
  echo "** SHELL set to $SHELL, but I cannot find that executable."
  errors=$(( $errors + 1 ))
fi

if [ ! -d ${HOME:?"You need to have your HOME set to your home directory"} ]
then
  echo "** HOME set to $HOME, but it's not a directory."
  errors=$(( $errors + 1 ))
fi

# Our first interesting test: are all the paths in PATH valid?

oldIFS=$IFS; IFS=":"     # IFS is the field separator. We'll change to ':'

for directory in $PATH
do
  if [ ! -d $directory ] ; then
      echo "** PATH contains invalid directory $directory"
      errors=$(( $errors + 1 ))
  fi
done

IFS=$oldIFS             # restore value for rest of script

# The following can be undefined, and they can also be a progname, rather
# than a fully qualified path.  Add additional variables as necessary for
# your site and user community.

validate "EDITOR" $EDITOR
validate "MAILER" $MAILER
validate "PAGER"  $PAGER

# and, finally, a different ending depending on whether errors > 0

if [ $errors -gt 0 ] ; then
  echo "Errors encountered. Please notify sysadmin for help."
else
  echo "Your environment checks out fine."
fi

exit 0