#!/bin/bash   

#the shebang, or some call it the hashpling! For it to work, the shebang (#!) must be the first two bytes in the file. 
              #then anything following it will be considered the path to the interpreter (bash, perl, tcl or whatever.)
              #Speaking of whatever, bash stands for Bourne Again Shell, and is a bourne shell(sh) variant. Another family of shells
	      #in unix are based on the C shell (csh). Bash is the default shell in linux.
	      #also, remember that a user must have at least read and execute permissions on the script in order
	      #to run it.


RPMDIR="/opt/rh7.1/redhat/RPMS"               #no spaces allowed in shell variable assignments
NEWRPMDIR="/opt/rh7.1/redhat/newrpms"
OLDRPMDIR="/opt/rh7.1/redhat/oldrpms"
TMPDIR="/opt/rh7.1/redhat/tmp"

export RPMDIR NEWRPMDIR OLDRPMDIR  #exporting the values makes them available to subshells - eg all of the commands we call in this script. 

for i in $(ls $NEWRPMDIR)     #yikes, a variable, for loop and command substitution in a single line! 
  do                          #there are for, while, and until loops - all use the do-done grammar.

  t=$(echo $i |  sed 's/-[0-9]\././g' | cut -f1 -d.)   #another command substitution to set the value of $t. notice a couple of things here.
                                                       #first, we don't use the $ notation when assigning the value of a variable,
                                                       #only when calling it - as when we echo $i from within the command substitution.
                                                       #also this syntax for command substitution - $(command) is the same as the
                                                       #old-fashioned bourne shell syntax `command`. what is command substitution?
                                                       #the output of the command in the parenthesis will be substituted for the
                                                       #command itself. So the line 'echo "$(date)"' will run as 'echo "Thu Aug 9 14:27:30 PDT 2001"'
                                                       #and produce the output 'Thu Aug 9 14:27:30 PDT 2001'. On this line we also see
                                                       #a classic unix pipeline, where the standard out from one command becomes the 
                                                       #standard in for the next.
 
                                                       
  echo $t >> $TMPDIR/names.tmp                         #redirection.  >> redirects STDOUT to a file by concatenating to the end of the file.
                                                       # > redirects STDOUT to file by overwriting the file.


  mv $RPMDIR/$t[-][0-9]*i386.rpm $OLDRPMDIR/ 2>>$TMPDIR/baddies.tmp   #more redirection; this time we are redirecting STDERR, standard
                                                                      #error or any error messages that result from this command to
                                                                      #a file. It's important to use >> while you're in a loop
                                                                      #because otherwise you'll overwrite the contents of the file
                                                                      #on every iteration of the loop! The special variables 0 1 2
                                                                      #are STDIN STDOUT and STDERR. By default they are your keyboard/mouse,
                                                                      #the screen, and the screen. But you can redirect them at will.
								        


done                       #closes the loop



#checking for discrepencies
ourold=$(ls $OLDRPMDIR | wc -l)         #more command substitution
ournew=$(ls $NEWRPMDIR | wc -l)

if [ -s $TMPDIR/baddies.tmp ] || [ $ourold != $ournew ]                 #at last some logic! the if statement takes the basic form of 
                                                                        #if (condition) then (commands) else (commands) fi (closes the if)  
                                                                        #we also have the test command, which takes the form of
                                                                        # "test statement" or "[ statement ]" the space after the
                                                                        #square bracket is mandatory because the [ is considered a command.
									#read the test man page for lots of fun.
									#also notice the logical or (||) between two tests. If one OR
									# the other is true, the commands following 'then' will run.
 									#there is also an optional elif.

   then
      mail -s "RPM update is screwed up!" brenda < $TMPDIR/baddies.tmp  #redirecting STDIN with <. the standard in for the mail command 
                                                                           #will be the contents of our baddies.tmp file
      mv $OLDRPMDIR/* $RPMDIR
      exit				#bail out of the script now.

    else
       mv $NEWRPMDIR/* $RPMDIR
       mv $OLDRPMDIR $OLDRPMDIR$(date +\%y\%m\%d) ; rm -f $TMPDIR/*.tmp     #commands can be seperated by  ;
       mkdir $OLDRPMDIR

fi		#closes the if statement