Carrying a variable through a series of script steps to print that variable's value in the script output

Another homework assignment for me ...
man export was no help at all; nor sudo apt-get install export

Online I found https://linuxconfig.org/learning-linux-commands-export
which introduced the concept of BUILTINS, and man BUILTINS provides
assurance that export and a lot of other commands, some of which I've taken for
granted, are real.

My first script has an obviously misplaced apostrophe [']:
sudo nmap -Pn -sn -T2 --max-retries 8 -iL Listed-IPv4[']s.txt -oG - | grep "Host:" '-' | awk '{print $2,$3}' '-' | sed 's/()/(No_DNS)/g' | tr -d '()' | grep -v "No_DNS" '-' > nMap-I-Listed-IPv4s.txt

The second script in the original posting wasn't quite right, as nmap expects only
one input variable; here's the correction:
awk '{print $2}' nMap-I-Listed-IPv4s.txt | sudo nmap -Pn -sn -T2 --max-retries 8 -iL '-' -oG - | grep "Host:" '-' | awk '{print $2,$3}' '-' | sed 's/()/(No_DNS)/g' | tr -d '()' > nMap-II-Listed-IPv4s.txt

Applying Lloyd's constructive suggestion depends on syntax which I haven't yet worked out.

My intent is, at each step in the script, to assign the $1 variable to a name called IPv4
and the $2 variable to the name PTR and then to place PTR in the -iL PTR position in the
arguments of nmap and IPv4 in the awk statement printing the outputs: awk '{print IPv4,$2,$3}' '-'

Here's my attempt to apply the declare command in my context:
awk '{print $1,$2}' nMap-I-Listed-IPv4s.txt | declare -x IPv4=$1 | declare -x PTR=$2 | awk '{print $2}' nMap-I-Listed-IPv4s.txt | sudo nmap -Pn -sn -T2 --max-retries 8 -iL '-' -oG - | grep "Host:" '-' | sed 's/()/(No_DNS)/g' | tr -d '()' | awk '{print IPv4,PTR,$2,$3}' '-' | awk '{print IPv4,PTR,$2,$3}' '-'|more

The first part of the script extracts the variables IPv4 ($1) and PTR ($2)
from the file (nMap-I-Listed-IPv4s.txt) created by the first script in my
original posting and uses the declare command to assign those two values:
awk '{print $1,$2}' nMap-I-Listed-IPv4s.txt | declare -x IPv4=$1 | declare -x PTR=$2

The second part of my proposed script initiates the nmap command which uses only
the current value of the $2 column in the source file to look up its IPv4 address:
awk '{print $2}' nMap-I-Listed-IPv4s.txt | sudo nmap -Pn -sn -T2 --max-retries 8 -iL '-' -oG -
which has two outputs: The newly retrieved IPv4 address and the value of $2 being
looked up with some extraneous text that is removed with grep, sed, and tr:
grep "Host:" '-' | sed 's/()/(No_DNS)/g' | tr -d '()'

Following the grep command I attempt to retrieve the stored values of IPv4 and PTR:
awk '{print IPv4,PTR,$2,$3}' '-'

Alas, this script runs, but fails to deliver.
I could make a set of 5,672 individual scripts, print a list of all 5,672 pairs, then
hand the variables one-at-a-time to the nmap command, print out another list of 5,672 new
pairs, and then match the lists side-by-side ...

Magic Banana infers from my scripting attempts that only paste may work.

Paste is handy for building multi-line scripts ...

Here's another attempt:
export PTR | awk -v PTR=$2 '{print $PTR}' nMap-I-Listed-IPv4s.test.txt | sudo nmap -Pn -sn -T2 --max-retries 8 -iL '-' -oG - | grep "Host:" '-' | sed 's/()/(No_DNS)/g' | tr -d '()' | sed 's/Host://g' | sed 's/Status://g' | sed 's/Up//g' | awk '{print $0,declare -p PTR}' '-' |more
and some selected output:
40.77.178.124 msnbot-40-77-178-124.search.msn.com 0
40.77.178.124 msnbot-40-77-178-124.search.msn.com 0
40.77.178.223 msnbot-40-77-178-223.search.msn.com 0
40.77.178.223 msnbot-40-77-178-223.search.msn.com 0
40.77.178.235 msnbot-40-77-178-235.search.msn.com 0
40.77.178.235 msnbot-40-77-178-235.search.msn.com 0
40.77.179.86 msnbot-40-77-179-86.search.msn.com 0
40.77.179.86 msnbot-40-77-179-86.search.msn.com 0
40.77.181.110 msnbot-40-77-181-110.search.msn.com 0
40.77.181.110 msnbot-40-77-181-110.search.msn.com 0
40.77.188.24 msnbot-40-77-188-24.search.msn.com 0
40.77.188.24 msnbot-40-77-188-24.search.msn.com 0
40.77.188.7 msnbot-40-77-188-7.search.msn.com 0
40.77.188.7 msnbot-40-77-188-7.search.msn.com 0
40.77.189.28 msnbot-40-77-189-28.search.msn.com 0
40.77.189.28 msnbot-40-77-189-28.search.msn.com 0

42.236.10.100 hn.kd.ny.adsl 0
92.242.140.21 unallocated.barefruit.co.uk 0
42.236.10.103 hn.kd.ny.adsl 0
92.242.140.21 unallocated.barefruit.co.uk 0
...
42.236.99.86 hn.kd.ny.adsl 0
92.242.140.21 unallocated.barefruit.co.uk 0

The identical pairs represent resolvable PTR's;
the non-identical pairs generally represent unresolvable PTR's.
The ...vodacom pair were somehow missed by barefruit error handling.

This script is on the right track:
Nmap was fed two variables (IPv4 and PTR) but only responded to the exported PTR variable.
However, awk's print function responds with both the 1st & 2nd columns (all that remain
after all those sed & tr commands) without regard to which one(s) are explicitly requested.

Without use of the export command, here's what happens:
awk '{print $2}' nMap-I-Listed-IPv4s.test.txt | sudo nmap -Pn -sn -T2 --max-retries 8 -iL '-' -oG - | grep "Host:" '-' | sed 's/()/(No_DNS)/g' | tr -d '()' | sed 's/Host://g' | sed 's/Status://g' | sed 's/Up//g' | awk '{print $1,$2}' '-' |more
and the condensed output:
40.77.178.124 msnbot-40-77-178-124.search.msn.com
40.77.178.223 msnbot-40-77-178-223.search.msn.com
40.77.178.235 msnbot-40-77-178-235.search.msn.com
40.77.179.86 msnbot-40-77-179-86.search.msn.com
40.77.181.110 msnbot-40-77-181-110.search.msn.com
40.77.188.24 msnbot-40-77-188-24.search.msn.com
40.77.188.7 msnbot-40-77-188-7.search.msn.com
40.77.189.28 msnbot-40-77-189-28.search.msn.com
... two missing rows where the ...
... vodacom entries once were ...
41.146.154.95 8ta-146-154-95.telkomadsl.co.za
92.242.140.21 unallocated.barefruit.co.uk
92.242.140.21 unallocated.barefruit.co.uk
4.14.17.198 COLORADO-SP.ear1.Dallas1.Level3.net
42.156.138.3 shenmaspider-42-156-138-3.crawl.sm.cn
92.242.140.21 unallocated.barefruit.co.uk
92.242.140.21 unallocated.barefruit.co.uk
92.242.140.21 unallocated.barefruit.co.uk
92.242.140.21 unallocated.barefruit.co.uk
...
92.242.140.21 unallocated.barefruit.co.uk
Without any of the subsequent text processing:
awk '{print $2}' nMap-I-Listed-IPv4s.test.txt | sudo nmap -Pn -sn -T2 --max-retries 8 -iL '-' -oG - | awk '{print $0}' '-' |more
The script finishes, having skipped the two vodacom entries, with the statement that 42 entries
(of 44 in the source file) were scanned, and all were "up" which is a rare occurrence in my experience.

Lloyd suggested that I substitute
awk -v "variable=$PTR" '{print $0, variable}'
for
awk '{print $0,declare -p PTR}'
at the end of my trial script:
export PTR | awk -v PTR=$2 '{print $PTR}' nMap-I-Listed-IPv4s.test.txt | sudo nmap -Pn -sn -T2 --max-retries 8 -iL '-' -oG - | grep "Host:" '-' | sed 's/()/(No_DNS)/g' | tr -d '()' | sed 's/Host://g' | sed 's/Status://g' | sed 's/Up//g' | awk -v "variable=$PTR" '{print $0, variable}' '-' |more
producing the exact same output without the trailing zero's,
but there should have been three columns, the first two for the outputs of the nmap script
and one for the input (?) value of variable=$PTR, which would have satisfied the original
posting's intent. In my other [rejected] attempts at the script, both columns of the original
file are printed whichever way I preface the script (exporting PTR or IPv4). The most recent two
scripts (Lloyd's and mine) at least produce two lines, an input pair of IPv4 and PTR, followed
by an output pair (nmap's IPv4 and the PTR) not always matching the inputs, except for the two
different vodacom rows, unfortunately.

At present, even placing the input file next to nmap's outputs without any use of export
or awk's -v argument would have almost done the trick, but for nmap's ignoring of the vodacom
inputs, as otherwise nmap's outputs are in the same sequence as the inputs.

This is progress, as there is a comparison between inputs and outputs.

Noted in some exasperation:
For example:
vc-gp-n-41-13-200-206.umts.vodacom.co.za
Can be almost trivially resolved by stripping the letters,
replacing the dashes (-) with dots (.) and then
using dig -x:
Start with: vc-gp-n-41-13-200-206.umts.vodacom.co.za
Strip out the letters:-41-13-200-206.
Replace the dashes with dots and remove leading & trailing punctuation: 41.13.200.206
dig -x 41.13.200.206:
ANSWER SECTION:
206.200.13.41.in-addr.arpa. 4670 IN PTR vc-gp-n-41-13-200-206.umts.vodacom.co.za
They're not all this straightforward; the octets are often rearranged to hinder resolution,
and there are two dozen permutations of the 1234 octet sequence.

It turns out that the following script:
grep -E -o "([0-9]{1,3}[\.]){3}[0-9]{1,3}" <(awk '{print $2}' nMap-I-Listed-IPv4s.test.txt)
Extracts only two IPv4 addresses from the target file, nMap-I-Listed-IPv4s.test.txt:
41.189.45.31
41.236.190.247
And these aren't the two vodacom PTRs' addresses, because the script isn't designed
to handle octets separated by dashes instead of dots.

Another script does gather the eleven dash-separated octets after a single change:
grep -E -o "([0-9]{1,3}[\-]){3}[0-9]{1,3}" <(awk '{print $2}' nMap-I-Listed-IPv4s.test.txt)
40-77-178-124
40-77-178-223
40-77-178-235
40-77-179-86
40-77-181-110
40-77-188-24
40-77-188-7
40-77-189-28
41-13-200-206
41-13-20-163
42-156-138-3

Sed can then be used to change those dashes to dots: sed 's/\-/\./g'
grep -E -o "([0-9]{1,3}[\-]){3}[0-9]{1,3}" <(awk '{print $2}' nMap-I-Listed-IPv4s.test.txt) | sed 's/\-/\./g'
40.77.178.124
40.77.178.223
40.77.178.235
40.77.179.86
40.77.181.110
40.77.188.24
40.77.188.7
40.77.189.28
41.13.200.206
41.13.20.163
42.156.138.3

But those nice-looking IPv4 addresses may still not resolve without being put back in their original order.

There are two or more forms of exasperation at play ...
Magic Banana's exasperation is over my age-related difficulty in remembering what I did last week ...
Mine is over the slow response of software developers in updating the dig command to deal with
"advances" in the methods of obfuscating server/Pointer names.

With apologies to Magic Banana, I'm not going to get any younger; I'm concentrating my efforts
on getting older.

Apache servers have been allowing their deprecated gratuitous hostname lookups to continue, though
I've noticed that the Webalizer data published online is increasingly free of those alphanumeric
abominations. That's not the main issue, though: the raw addresses too often resolve to untraceable
pointer names, and it would benefit the honest users of the Internet if the maliciously named
pointers were detected [and then flagged] by double lookups.

Here's my current way of dealing with those buried addresses:
grep -E -o "([0-9]{1,3}[\.\-]){3}[0-9]{1,3}" <(awk '{print $2}' nMap-I-Listed-IPv4s.txt) | sed 's/\-/\./g' | sort -u
Combining the field separators (.) and (-) in a single script increases the number of addresses
extracted from 434 using just (.) or 3,825 using just (-) to 4,366 using both at once.

I notice on further reflection that reversing the order of [\.\-] to [\-\.] yields only 434 addresses:
wc -l <(grep -E -o "([0-9]{1,3}[\-\.]){3}[0-9]{1,3}" <(awk '{print $2}' nMap-I-Listed-IPv4s.txt) | sed 's/\-/\./g' |sort -u)
Magic Banana will not like this ad hoc approach ...

The following twenty-four-step script looks up the PTR's of the permutations of the sequences of
four octets of the extracted IPv4 addresses:
awk '{print $0}' nMap-I-Extracted-IPv4s.test.txt | sed 's/\./\t/g' | awk '{print $1"."$2"."$3"."$4}' '-' | sudo nmap -Pn -sn -T2 --max-retries 8 -iL '-' oG - | grep "Nmap scan report for " '-' | awk '{print $6,$5}' '-' | sed 's/()/(No_DNS)/g' | tr -d '()' > nMap-I-Extracted-IPv4s.1234-oGnMap.test.txt ;
awk '{print $0}' nMap-I-Extracted-IPv4s.test.txt | sed 's/\./\t/g' | awk '{print $1"."$2"."$4"."$3}' '-' | sudo nmap -Pn -sn -T2 --max-retries 8 -iL '-' oG - | grep "Nmap scan report for " '-' | awk '{print $6,$5}' '-' | sed 's/()/(No_DNS)/g' | tr -d '()' > nMap-I-Extracted-IPv4s.1243-oGnMap.test.txt ;
...
awk '{print $0}' nMap-I-Extracted-IPv4s.test.txt | sed 's/\./\t/g' | awk '{print $4"."$3"."$2"."$1}' '-' | sudo nmap -Pn -sn -T2 --max-retries 8 -iL '-' oG - | grep "Nmap scan report for " '-' | awk '{print $6,$5}' '-' | sed 's/()/(No_DNS)/g' | tr -d '()' > nMap-I-Extracted-IPv4s.4321-oGnMap.test.txt ;
Saved as nMap-I-Extracted-IPv4s.4321.test.txt (attached) and made executable, it produces a
collected output consisting of mixed unresolved IPv4 addresses and resolved ones, separated
with the script:
cat nMap-I-Extracted-IPv4s.????-oGnMap.test.txt | sort -u | awk '{print $2}' '-' | sed '/^$/d' '-' > nMap-I-Extracted-IPv4s-to-Candidate-PTRs.test.txt
Which when joined with Col$2 of the original list in nMap-I-Listed-IPv4s.txt:
join -1 1 -2 2 <(sort nMap-I-Extracted-IPv4s-to-Candidate-PTRs.test.txt) <(sort -k 2,2 nMap-I-Listed-IPv4s.test.txt) | awk '{print $2,$1}' '-' > nMap-II-Resolved-PTRs.test.txt
Lists thirteen of the fourteen original address-containing PTR's.
The unresolved one looks as though it's further obfuscated with a numeral adjacent to a letter:
8ta-146-154-95.telkomadsl.co.za
But that PTR is directly resolved with dig.
The other thirteen are all in the 1234 category of the 24 permutations; I'll run the same series
of scripts on the main 5,672-row list of nMap-I-Listed-IPv4s.txt and report back later.

To no one's surprise, Magic Banana's script both works better and looks better than mine,
though I did modify it a little for my application:
BEGIN {
if (sep == "")
sep = " "
FS = "[^0-9]+"
OFS = "." }
{
k = 0
for (i = 0; k < 4 && ++i <= NF; )
if ($i != "" && $i < 256)
a[++k] = $i
else
k = 0 }
k == 4 {
print a[1], a[2], a[3], a[4] sep a[1], a[2], a[4], a[3] sep a[1], a[3], a[2], a[4] sep a[1], a[3], a[4], a[2] sep a[1], a[4], a[2], a[3] sep a[1], a[4], a[3], a[2] sep a[2], a[1], a[3], a[4] sep a[2], a[1], a[4], a[3] sep a[2], a[3], a[1], a[4] sep a[2], a[3], a[4], a[1] sep a[2], a[4], a[1], a[3] sep a[2], a[4], a[3], a[1] sep a[3], a[1], a[2], a[4] sep a[3], a[1], a[4], a[2] sep a[3], a[2], a[1], a[4] sep a[3], a[2], a[4], a[1] sep a[3], a[4], a[1], a[2] sep a[3], a[4], a[2], a[1] sep a[4], a[1], a[2], a[3] sep a[4], a[1], a[3], a[2] sep a[4], a[2], a[1], a[3] sep a[4], a[2], a[3], a[1] sep a[4], a[3], a[1], a[2] sep a[4], a[3], a[2], a[1] }
And so the execution becomes:
awk -f ./Script-MB-4321-permutations -v sep='\n' <(awk '{print $2}' nMap-I-Listed-IPv4s.txt) | sudo nmap -Pn -sn -T2 --max-retries 8 -iL '-' oG - | grep "Nmap scan report for " '-' | awk '{print $6,$5}' '-' | sed 's/()/(No_DNS)/g' | tr -d '()' > nMap-I-MB-Extracted-IPv4s.Permutations-oGnMap.txt

Followed by a join to the PTR column of the source file:
join -1 2 -2 1 <(sort -k 2,2 nMap-I-MB-Extracted-IPv4s.Permutations-oGnMap.txt) <(awk '{print $2}' nMap-I-Listed-IPv4s.txt | sort -k 1,1) | awk '{print $2,$1}' '-' | sort -u > nMap-II-Resolved-PTRs-MB.txt
Capturing 5096 of 5672 original rows, with many inseparable PTR's brought in by association:
awk -f ./Script-MB-1234-Followup -v sep=' ' <( awk '{print $2}' nMap-II-Resolved-PTRs-MB.txt) > nMap-II-Separable-4321-PTRs-MB.txt
Where 4432 rows out of the original 5096 rows are separable.
Magic Banana's original script can be further modified to test the output file for separability:
BEGIN {
if (sep == "")
sep = " "
FS = "[^0-9]+"
OFS = "." }
{
k = 0
for (i = 0; k < 4 && ++i <= NF; )
if ($i != "" && $i < 256)
a[++k] = $i
else
k = 0 }
k == 4 {
print a[1], a[2], a[3], a[4] sep $0 }
Comm will find the inseparable ones:
comm -23 <(awk '{print $2}' nMap-II-Resolved-PTRs-MB.txt | sort) <(awk '{print $2}' nMap-II-Separable-4321-PTRs-MB.txt | sort) | uniq -c '-' > nMap-II-Inseparable-4321-PTRs-MB.txt
These may be associated with other servers of other PTR's; that will take a little more work; see attachment.