Compare two files and matched line send to new file

Question

I have two files

file1.txt

a|1|cd
a|2|cd
a|4|cd

file2.txt

a|0001|hj|df
a|0002|ed|nb
a|0003|vf|za
a|0004|er|ns
a|0005|oi|lk

I need a create new file with the lines matched by de second column of the files, I try by then next code

awk -F"|" 'NR==FNR{a[$2]++;next} a[$2] ' file1.txt file2.txt

but no found records, because file1.txt in second column doesn't contain 0 at the left I have the instruction

awk -F"|" 'NR==FNR{a[$(printf("%09d\n", $2))]++;next} a[$2]'

but doesn't work.

The result must be:

file3.txt

a|0001|hj|df
a|0002|ed|nb
a|0004|er|ns

Answer 1

Adding zero to field forces awk to treat it as a number, not a string:

$ awk -F"|" 'NR==FNR{a[$2+0]++;next} a[$2+0] ' file1.txt file2.txt
a|0001|hj|df
a|0002|ed|nb
a|0004|er|ns

As a string 0001 is different from 1. By adding zero to each, we convert them to numbers which results in the comparison that you want.