What does this awk command do? - awk

Question

What does this awk command do?
awk 'NR > 1 {for(x=1;x<=NF;x++) if(x == 1 || (x >= 4 && x % 2 == 0))
printf "%s", $x (x == NF || x == (NF-1) ? "\n":"\t")}' depth.txt
> depth_concoct.txt
I think
NR > 1 means it starts from second line,
for(x=1;x<=NF;x++) means for every fields,
if(x == 1 || (x >= 4 && x % 2 == 0)) means if x equals 1 or (I don' understand the codes from this part and so on)
and I know that the input file for awk is depth.txt and the output of awk will be saved to depth_concoct.txt.
What does the codes in the middle mean?

Answer 1

$ awk '
NR > 1 { # starting from the second record
for(x=1;x<=NF;x++) # iterate every field
if(x == 1 || (x >= 4 && x % 2 == 0)) # for 1st, 4th and every even-numbered field after 4th
printf "%s", # print the field and after it
$x (x == NF || x == (NF-1) ? "\n":"\t") # a tab or a newline if its the last field
}' depth.txt > depth_concoct.txt
(x == NF || x == (NF-1) ? "\n":"\t") is called conditional operator, in this context it's basically streamlined version of:
if( x == NF || x == (NF-1) ) # if this is the last field to be printed
printf "\n" # finish the record with a newline
else # else
printf "\t"` # print a tab after the field

Answer 2

you can rewrite it as below, which should be trivial to read.
$ awk `NR>1 {printf "%s", $1;
for(x=4;x<=NF;x+=2) printf "\t%s", $x;
print ""}' inputfile > outputfile
the complexity of the code is sometimes just an implementation detail.
prints first and every second field starting from the 4th.
Assume your file has 8 fields, this is equivalent to
$ awk -v OFS='\t' 'NR>1{print $1,$4,$6,$8}' inputfile > outputfile