Add null to the columns which are empty - perl

Question

I am trying to put null to the columns which are empty using perl or awk, to find the number of column , header's column count can be used. I tried to perform the solution using perl and some regex. However, the output looks very close to the desired output but if noticed carefully row number one is showing incorrect data.
Input data:
id name type foo-id zoo-id loo-id-1 moo-id-2
----- --------------- ----------- ------ ------ ------ ------
0 zoo123 soozoo 8 31 32
51 zoo213 soozoo 48 51
52 asz123 soozoo 47 52
53 asw122 soozoo 1003 53
54 fff123 soozoo 68 54
55 sss123 soozoo 75 55
56 ssd123 soozoo 76 56
Expected Output:
0 zoo123 soozoo 8 null 31 32
51 zoo213 soozoo 48 51 null null
52 asz123 soozoo 47 52 null null
53 asw122 soozoo 1003 53 null null
54 fff123 soozoo 68 54 null null
55 sss123 soozoo 75 55 null null
56 ssd123 soozoo 76 56 null null
Very close to solution but row-1 is showing incorrect data:
echo "$x"|grep -E '^[0-9]+' |perl -ne 'm/^([\d]+)(?:\s+([\w]+))?(?:\s+([-\w]+))?(?:\s+([\d]+))?(?:\s+([\d]+))?(?:\s+([\d]+))?(?:\s+([\d]+))?/;printf "%s %s %s %s %s %s %s\n", $1, $2//"null", $3//"null",$4//"null",$5//"null",$6//"null",$7//"null"' |column -t
0 zoo123 soozoo 8 31 32 null
51 zoo213 soozoo 48 51 null null
52 asz123 soozoo 47 52 null null
53 asw122 soozoo 1003 53 null null
54 fff123 soozoo 68 54 null null
55 sss123 soozoo 75 55 null null
56 ssd123 soozoo 76 56 null null

Answer 1

When you have a fixed-width string to parse, you'll find that unpack() is a better tool than regexes.
This should demonstrate how to do it. I'll leave it to you to convert it to a one-liner.
#!/usr/bin/perl
use strict;
use warnings;
use feature 'say';
use Data::Dumper;
while (<DATA>) {
next if /^\D/; # Skip lines that don't start with a digit
# I worked out the unpack() template by counting columns.
my #data = map { /\S/ ? $_ : 'null' } unpack('A7A14A16A8A8A8A8');
say join ' ', #data;
}
__DATA__
id name type foo-id zoo-id loo-id-1 moo-id-2
----- --------------- ----------- ------ ------ ------ ------
0 zoo123 soozoo 8 31 32
51 zoo213 soozoo 48 51
52 asz123 soozoo 47 52
53 asw122 soozoo 1003 53
54 fff123 soozoo 68 54
55 sss123 soozoo 75 55
56 ssd123 soozoo 76 56
Output:
$ perl unpack | column -t
0 zoo123 soozoo 8 null 31 32
51 zoo213 soozoo 48 51 null null
52 asz123 soozoo 47 52 null null
53 asw122 soozoo 1003 53 null null
54 fff123 soozoo 68 54 null null
55 sss123 soozoo 75 55 null null
56 ssd123 soozoo 76 56 null null

Answer 2

With GNU awk:
awk 'NR>2{ # ignore first and second row
NF=7 # fix number of columns
for(i=1; i<=NF; i++) # loop with all columns
if($i ~ /^ *$/){ # if empty or only spaces
$i="null"
}
print $0}' FIELDWIDTHS='7 14 16 8 8 10 8' OFS='|' file | column -s '|' -t
As one line:
awk 'NR>2{NF=7; for(i=1;i<=NF;i++) if($i ~ /^ *$/){$i="null"} print $0}' FIELDWIDTHS='7 14 16 8 8 10 8' OFS='|' file | column -s '|' -t
Output:
0 zoo123 soozoo 8 null 31 32
51 zoo213 soozoo 48 51 null null
52 asz123 soozoo 47 52 null null
53 asw122 soozoo 1003 53 null null
54 fff123 soozoo 68 54 null null
55 sss123 soozoo 75 55 null null
56 ssd123 soozoo 76 56 null null
See: 8 Powerful Awk Built-in Variables – FS, OFS, RS, ORS, NR, NF, FILENAME, FNR