|
|
BEGIN and END are two special patterns that give you a way to control initialization and wrap-up in an awk program. BEGIN matches before the first input record is read, so any statements in the action part of a BEGIN are done once, before the awk command starts to read its first input record. The pattern END matches the end of the input, after the last record has been processed.
The following awk program uses BEGIN to set the field separator to tab (\t) and to put column headings on the output. The field separator is stored in a built-in variable called FS. Although FS can be reset at any time, usually the only sensible place is in a BEGIN section, before any input has been read. The second printf statement of the program which is executed for each input line, formats the output into a table, neatly aligned under the column headings. The END action prints the totals. (Notice that a long line can be continued after a comma.)
BEGIN { FS = "\t"
printf "%10s %6s %5s %s\n",
"COUNTRY", "AREA", "POP", "CONTINENT" }
{ printf "%10s %6d %5d %s\n", $1, $2, $3, $4
area = area + $2; pop = pop + $3 }
END { printf "\n%10s %6d %5d\n", "TOTAL", area, pop }
With the file
countries
as input,
this program produces
COUNTRY AREA POP CONTINENT
USSR 8650 262 Asia
Canada 3852 24 North America
China 3692 866 Asia
USA 3615 219 North America
Brazil 3286 116 South America
Australia 2968 14 Australia
India 1269 637 Asia
Argentina 1072 26 South America
Sudan 968 19 Africa
Algeria 920 18 Africa
TOTAL 30292 2201