Hi Vijay8l,
Am trying to read directory/subdirectories and for files from a path recursively

Why not use File::Find instead of doing all the jobs yourself.

..reading file content(usually just 1 line in a file) and substituting space with comma from the line.
Are you trying to create a Comma-separated values files? If yes then see Text::CSV.

Just to give a head up, using File::Find and substitution function, I did something very close to what you wanted.

#!/usr/bin/perl
use warnings;
use strict;
use File::Find;

my $base_dir = '...';  # put in your base directory

find( \&wanted, $base_dir );

sub wanted {
    return if $_ eq '.' or $_ eq '..';
    if (-d) {
        print " >>> dive into: $_\n" if -d;
    }
    else {
        readout_file($_);  ## call subroutine readout_file
    }
}

sub readout_file {
    my ($filename) = @_;
    open my $fh, '<', $filename or die "can't open file:$!";
    while (<$fh>) {
        chomp;
        s/ /,/;        ## OR s/ /,/g; if you want 
        print $_, $/;  ## OR any other subroutine you want 
    }
 }
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