Please find code as below. I'm a bit of a noob, so it should all either be easy enough or commented. RSVP if there's anything needs explanation.

#!usr/bin/perl    -w-T

#ABOUT
# Objective: renames all .csv files (from MS Excel) in a given
#directory to <StationNumber><Parameter>.csv where <StationNumber> and
#<Parameter> are taken from the file contents.

#DETAIL
# Abstracts relevant information from a file, re-names the file to
#(typically):
#<GaugeRefNo>REev.csv for tipping-bucket rainfall gauges.
#<GaugeRefNo>RSst.csv for storage rainfall gauges.

#CODE
use strict;
use diagnostics;
use Cwd;

my %renamefiles=();
my $renamefiles;
my @keys=();
my $key;

{
my $files;
my @files=<c:/Storage/*.csv>;    #Reads all csv files

foreach(@files)
    {    my $open=$_;    #Read current file to process from array
        my $string;    #Slurp file line by line
        my $gaugeref;
        my $gaugeparam;
        my $currentdir;
        my $newdir;
        my $chaff;
        my $result;
        my $newname;
        my $oldname;
######TODO - Read $param from file contents
#        my $param="REev";    #For tipping bucket raingauges
        my $param="RSst";    #For storage raingauges
#        my $param="SG";        #For stage (level)
######
        my $extension="csv";

        #Strip filename to "/" in path
        $newdir=$_;$chaff=chop($newdir) while substr($newdir,length($n
+ewdir)-1)!~/\//;
        chdir $newdir;
                
        #PARSE IN
        open(INFILE,"<", $open) or die "Couldn't open $open $!";
        print "Opened $open \n";
        while(<INFILE>)    #Loop through lines
            {    $string=$_;
                # GET STATION NUMBER
                if (lc($string)=~ /(gauge ref|station number)/)
                    {    my $station=$string;    
                        chomp $station;
                        $chaff=chop($station) while substr($station,le
+ngth($station)-1)=~/\D/;    #drop chaff
                        $result.=chop($station) while substr($station,
+length($station)-1)=~/\d/;    #append hits
                        $gaugeref=reverse($result);
                        next;
                    };
            };
        close $open;
        $result="";#Clear
        $result.=chop($open) while substr($open,length($open)-1)!~/\//
+;#read filename from path until encounters /
        $oldname=reverse($result);
        $newname="$gaugeref$param.$extension";
        print "Old:$oldname\nNew: $newname\n";
        %renamefiles=($oldname=>$newname);

        @keys=sort keys %renamefiles;
        foreach $key(sort keys %renamefiles)
            {
            if (!(-w $oldname))
                {print "$oldname is not writeable\n";}
            else{
                use Stat::lsMode;
                my $mode = file_mode($oldname);
                print "Filemode is $mode\n";
                renamefile("$key","$renamefiles{$key}");
                };
            };
        };
};
    
######SUBS######
    sub renamefile{
        my $oldname=shift;
        my $newname=shift;
        my $success="";
        
        print qq{Attempting to rename $oldname to $newname\n};
        $success=rename $oldname, $newname;
        if ($success){print "Changed $oldname to $newname\n"}
        else
        {print "Failed to rename $oldname to $newname $!\n";exit};
    };
[download]

Thanks in for any help.