Nrthugu

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?

$ 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

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