Print a comma except on the last line in Awk

Question

I have the following script

awk \'{printf \"%s\", $1\"-\"$2\", \"}\' $a >> positions;

where $a stores the name of the fi

Answer 1

Enjoy this one:

awk '{printf t $1"-"$2} {t=", "}' $a >> positions

Yeh, looks a bit tricky at first sight. So I'll explain, first of all let's change printf onto print for clarity:

awk '{print t $1"-"$2} {t=", "}' file

and have a look what it does, for example, for file with this simple content:

1 A
2 B
3 C
4 D

so it will produce the following:

 1-A
 , 2-B
 , 3-C
 , 4-D

The trick is the preceding t variable which is empty at the beginning. The variable will be set {t=...} only on the next step of processing after it was shown {print t ...}. So if we (awk) continue iterating we will got the desired sequence.