I need the output in following way in perl - perl

Question

# File-
# a,b,c,d,e,f
# 1,2,3,4,3,2
# 9,8,7,6,5,0
# 2,3,4,6,7,8
# i need output like this:-
# a=1,d=4,c=3,a=9,d=6,c=7,a=2,d=6,c=4
# but my program gives this:-
# a=1,d=4,c=3a=9,d=6,c=7a=2,d=6,c=4 (there is no , after c and a)
my script is :-
open ($fh, 'parse.txt');
my #arr;
my $dummy=<$fh>;
while (<$fh>) {
chomp;
$a = substr $_, 0,1;
$b = substr $_, 6,1;
$c = substr $_, 4,1;
print "a=$a,d=$b,c=$c";
}
close (IN);

Answer 1

my $prefix = '';
while (<$fh>) {
chomp;
my #fields = split /,/;
print $prefix."a=$fields[0],d=$fields[3],c=$fields[2]";
$prefix = ',';
}
print("\n");
or
my #recs;
while (<$fh>) {
chomp;
my #fields = split /,/;
push #recs, "a=$fields[0],d=$fields[3],c=$fields[2]";
}
print(join(',', #recs), "\n");

Answer 2

Instead of printing out the values you could append them to a string and include a comma after the "c" value. Then at the end of the loop, erase the final comma from the string and print it out. There are some scalability problems if your input file is too large. But if it's a reasonable size there shouldn't be any substantial issue.
my $output;
my $dummy=<$fh>;
while (<$fh>) {
chomp;
$a = substr $_, 0,1;
$b = substr $_, 6,1;
$c = substr $_, 4,1;
$output .= "a=$a,d=$b,c=$c,";
}
chop $output;
print $output;

Answer 3

If you have fields with separators split the line and collect needed elements
use warnings;
use strict;
use feature 'say';
my $file = 'parse.txt';
open my $fh, '<', $file or die "Can't open $file: $!";
my $dummy = <$fh>;
my #res;
while (<$fh>)
{
my ($a, $d, $c) = (split /,/)[0,3,2];
push #res, "a=$a,d=$d,c=$c";
}
say join ',', #res;
or pick the order in the assignment
my ($a, $c, $d) = (split /,/)[0,2,3];