Thanks for your help and suggestions. I have read up on subroutines now and come up with the code below. I think this addresses a lot of the points and appears to work quite well but I don't see all of my data file (prev.txt) on screen. Have I still got something wrong? TIA S.

#!/usr/bin/perl -w
use strict;

my(@DATAFILE);

@DATAFILE=&readdata();

&testcode1(@DATAFILE);

&writedata(@DATAFILE);

#
# Subroutine for reading prev.txt into an array
#

sub readdata {
    open (PH, "prev.txt") || die "Cannot open prev.txt: $!";
    my(@DATA)=<PH>;
    chomp @DATA;
    close (PH);
    return(@DATA);
}

#
# Subroutine for writing array into prev.txt
#

sub writedata {
    my(@DATA)=@_;
    open (PH, ">prev.txt") || die "Cannot open prev.txt: $!";
    foreach(@DATA) {
        print PH "$_\n";
    }
    close (PH);
}

#
# Subroutines for various tests on the code
#

sub testcode1 {
    print "@_";
}
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