Question

I’m reading The UNIX Programming Environment and in Section 4.4, about awk, there is this sample code:

    awk '
    FILENAME != prevfile {   # new file
        NR = 1               # reset line number
        prevfile = FILENAME
    }
    NF > 0 {
        if ($1 == lastword)
            printf "double %s, file %s, line %d\n",$1,FILENAME,NR
        for (i = 2; i <= NF; i++)
            if ($i == $(i-1))
                printf "double %s, file %s, line %d\n",$i,FILENAME,NR
        if (NF > 0)
            lastword = $NF
    }' $*

Why is NF > 0 tested inside the block which already had a NF > 0 as a pattern?

Answer 1

Contained within the errata notes for this book:

Page 121, first program: test "if (NF > 0)" is unnecessary.

So it was a mistake made by the publisher and/or copy editor.