awk how to set the format output filename for multiple output

Question

I have a file (file.csv) which looks like this:

abc 123
abc 001
abc 014
bos 011
bos 034
bos 079
bos 004
...

PS: column 1 of file.csv has 27297 unique words in total, and file.csv has 789234 rows in total

I want to split it into multiple files basing on the first column. and I use awk to deal with it:

awk '{x=++i}{print $2 > "HG"x".txt"}' file.csv

however, the name of the output was HG1.txt, HG2.txt,..., HG27297.txt. what I want is that the file name of output should be formated, they should look like HG000001.txt, HG000002.txt,..., HG027297.txt.

Answer 1

{x=++i} would result in 2 variables, x and i, which both have the same value as the builtin variable NR (and FNR).

print $2 > "HG"x".txt" is undefined behavior due to no parens around the expression on the right side of >.

Not closing output files as you go would result in a "too many open files" error once you get past a threshold when using all but GNU awk.

Assuming your input is grouped by the first field values as shown in your example (if not, run sort on the input first):

awk '$1!=prev{close(out); out=sprintf("HG%06d.txt",++c); prev=$1} {print > out}' file.csv

Obviously change print > out to print $2 > out if you truly only want the 2nd column printed as in your code.