11.3.4 Printing Mailing Labels

Here is a “real-world”⁷⁹ program. This script reads lists of names and addresses and generates mailing labels. Each page of labels has 20 labels on it, two across and 10 down. The addresses are guaranteed to be no more than five lines of data. Each address is separated from the next by a blank line.

The basic idea is to read 20 labels’ worth of data. Each line of each label is stored in the line array. The single rule takes care of filling the line array and printing the page when 20 labels have been read.

The BEGIN rule simply sets RS to the empty string, so that awk splits records at blank lines (see section How Input Is Split into Records). It sets MAXLINES to 100, because 100 is the maximum number of lines on the page (20 * 5 = 100).

Most of the work is done in the printpage() function. The label lines are stored sequentially in the line array. But they have to print horizontally: line[1] next to line[6], line[2] next to line[7], and so on. Two loops accomplish this. The outer loop, controlled by i, steps through every 10 lines of data; this is each row of labels. The inner loop, controlled by j, goes through the lines within the row. As j goes from 0 to 4, ‘i+j’ is the jth line in the row, and ‘i+j+5’ is the entry next to it. The output ends up looking something like this:

line 1          line 6
line 2          line 7
line 3          line 8
line 4          line 9
line 5          line 10
…

The printf format string ‘%-41s’ left-aligns the data and prints it within a fixed-width field.

As a final note, an extra blank line is printed at lines 21 and 61, to keep the output lined up on the labels. This is dependent on the particular brand of labels in use when the program was written. You will also note that there are two blank lines at the top and two blank lines at the bottom.

The END rule arranges to flush the final page of labels; there may not have been an even multiple of 20 labels in the data:

# labels.awk --- print mailing labels

# Each label is 5 lines of data that may have blank lines.
# The label sheets have 2 blank lines at the top and 2 at
# the bottom.

BEGIN    { RS = "" ; MAXLINES = 100 }

function printpage(    i, j)
{
    if (Nlines <= 0)
        return

    printf "\n\n"        # header

    for (i = 1; i <= Nlines; i += 10) {
        if (i == 21 || i == 61)
            print ""
        for (j = 0; j < 5; j++) {
            if (i + j > MAXLINES)
                break
            printf "   %-41s %s\n", line[i+j], line[i+j+5]
        }
        print ""
    }

    printf "\n\n"        # footer

    delete line
}

# main rule
{
    if (Count >= 20) {
        printpage()
        Count = 0
        Nlines = 0
    }
    n = split($0, a, "\n")
    for (i = 1; i <= n; i++)
        line[++Nlines] = a[i]
    for (; i <= 5; i++)
        line[++Nlines] = ""
    Count++
}

END {
    printpage()
}