awk command fails with command substitution - bash

Question

Running this command fails:
$(printf "awk '{%sprint}'" $(tail -n +2 file.txt | cut -f2 | sort | uniq | awk 'BEGIN{a=1}{printf "gsub(\"%s\",%i);", $1,a++}')) file.txt
It gives the following error:
awk: '
awk: ^ invalid char ''' in expression
However, if I run the substituted command, I get this:
awk '{gsub("ACB",1);gsub("ASW",2);gsub("BEB",3);gsub("CDX",4);gsub("CEU",5);gsub("CHB",6);gsub("CHS",7);gsub("CLM",8);gsub("ESN",9);gsub("FIN",10);gsub("GBR",11);gsub("GIH",12);gsub("GWD",13);gsub("IBS",14);gsub("ITU",15);gsub("JPT",16);gsub("KHV",17);gsub("LWK",18);gsub("MSL",19);gsub("MXL",20);gsub("PEL",21);gsub("PJL",22);gsub("PUR",23);gsub("STU",24);gsub("TSI",25);gsub("YRI",26);print}'
which I can run like so:
awk '{gsub("ACB",1);gsub("ASW",2);gsub("BEB",3);gsub("CDX",4);gsub("CEU",5);gsub("CHB",6);gsub("CHS",7);gsub("CLM",8);gsub("ESN",9);gsub("FIN",10);gsub("GBR",11);gsub("GIH",12);gsub("GWD",13);gsub("IBS",14);gsub("ITU",15);gsub("JPT",16);gsub("KHV",17);gsub("LWK",18);gsub("MSL",19);gsub("MXL",20);gsub("PEL",21);gsub("PJL",22);gsub("PUR",23);gsub("STU",24);gsub("TSI",25);gsub("YRI",26);print}' file.txt
And it works perfectly. What am I doing wrong?
#ChrisLear gave me a working solution, but I still don't quite understand what the command solution is doing. Here's the working code:
$(printf "awk {%sprint}" $(tail -n +2 file.txt | cut -f2 | sort | uniq | awk 'BEGIN{a=1}{printf "gsub(\"%s\",%i);", $1,a++}')) file.txt
The single quotes around {%sprint} are removed. Why do those single quotes break the command substitution?
edit: changed backtick to $(...) notation. Also added solution I don't understand.

Answer 1

Try removing the quotes from the command being generated.
`printf "awk {%sprint}" $(tail -n +2 file.txt | cut -f2 | sort | uniq | awk 'BEGIN{a=1}{printf "gsub(\"%s\",%i);", $1,a++}')` file.txt
For an explanation, see the accepted answer at Why does command substitution change how quoted arguments work?

Answer 2

It looks like you're trying to take a bunch of unique 2nd fields from a file starting at line 2 and map those to numbers based on their alphabetic ordering, then apply the change to the same file. If so then with GNU awk for sorted_in and inplace editing that'd be:
awk -i inplace '
NR==FNR {
if (NR>1) {
map[$2]
}
next
}
FNR==1 {
PROCINFO["sorted_in"] = "#ind_str_asc"
for (str in map) {
map[str] = ++i
}
}
{
$2 = map[$2]
print
}
' file.txt
If that's not what you need then edit your question to show concise, testable sample input and expected output.