Shantanu's Blog

October 27, 2023

awk Case Study - 1

 # cat countries.txt

USSR    8649    275     Asia
Canada  3852    25      North America
China   3705    1032    Asia
USA     3615    237     North America
Brazil  3286    134     South America
India   1267    746     Asia
Mexico  762     78      North America
France  211     55      Europe
Japan   144     120     Asia
Germany 96      61      Europe
England 94      56      Europe

awk 'BEGIN { FS = "\t" # make tab the field separator
                 printf("%10s %6s %5s %s\n\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) } ' countries.txt

# check if country name starts ith Japa

awk '$1 ~ /Japa/' countries.txt

# & is special. It echoes the original string change to aba

awk '{ gsub(/a/, "&b&"); print }' countries.txt

# Change country names

awk '{ gsub(/North America/, "NA"); print }' countries.txt

# Change country names

awk 'BEGIN {FS = OFS = "\t"}

$4 == "North America" {$4 = "NA" }

$4 == "South America" {$4 = "SA" }

{print }' countries.txt

# add a column for computation

awk 'BEGIN { FS = OFS = "\t" }

{ $5 = 1000 * $3 / $2; print }' countries.txt

# conditional expression 

awk '{ print ($2 < 100 ? "less than 100" : "$2 greater than 100 " NR) }' countries.txt

# Assignment Operators

awk '$4 == "Asia" { pop = pop + $3; n = n + 1 }

END { print "Total population of the", n,

"Asian countries is", pop, "million."}' countries.txt

awk '$3 > maxpop { maxpop = $3; country = $1 }

END {print "country with largest population:",

country, maxpop }' countries.txt

# second field is a string of digits

awk 'BEGIN { digits = "^[0-9]+$" } $2 ~ digits' countries.txt

# regular expression built up from components

awk 'BEGIN {

sign = "[+-]?"

decimal= "[0-9]+[.]?[0-9]*"

fraction= "[.][0-9]+"

exponent= "([eE]" sign "[0-9]+)?"

number= "^" sign "(" decimal "!" fraction ")" exponent "$"

}

$1 ~ number' countries.txt

# Setting $1 forces awk to recompute $0 

# the fields are now separated by a blank 

# (the default value of OFS), no longer by a tab

awk '{ $1 = substr($1, 1, 3); print $0 }' countries.txt

# print first 3 chars of first column in a line

awk '{ s = s substr ( $1 , 1 , 3 ) " " } END { print substr(s, 1, length(s)-1) }' countries.txt

# group by sum

awk '/Asia/ { pop["Asia"] += $3 }

/Europe/ { pop["Europe"] += $3}

END {

print "Asian population is", pop["Asia"], "million."

print "European population is", pop["Europe"], "million."}' countries.txt

# group by sum SQL like query

awk 'BEGIN { FS = "\t" }  {pop[$4] += $3 } END { for (name in pop) print name, pop[name] }' countries.txt

# reverse order using array

awk '{ x[NR] = $0 }

END { for (i = NR; i > 0; i--) print x[i] }' countries.txt

# return all fields

awk '{i = 1; while (i <= NF) { print $i; i++ }}' countries.txt

awk '{for (i = 1; i <= NF; i++) print $i }' countries.txt

# User Defined Function

awk '{print max($1, max(S2,S3))} #print maximum of $1, $2, $3

function max(m, n) {

return m > n ? m : n

}' countries.txt

# Output Separators

awk 'BEGIN { OFS = ":"; ORS = "\n\n" } { print $1, $2 }' countries.txt

# redirect to file

awk '$3 > 100 { print $1, $3 >"bigpop.txt" }' countries.txt

awk '{ print($1, $3) > ($3 > 100 ? "big.txt" : "small.txt") }' countries.txt

# Field Separator

awk 'BEGIN {FS = ",[ \t]*![ \t]+"} {print}' countries.txt

awk -F ',[ \t]*![ \t]+' '{print}' countries.txt

_____

awk 'BEGIN { FS = "\t" }

{ printf("%s:%s:%d:%d:%.1f\n", $4, $1, $3, $2, 1000*$3/$2) | "sort -t: +0 -1 +4rn"}' countries.txt

awk 'BEGIN { FS = "\t" }

{ printf("%s:%s:%d:%d:%.1f\n", $4, $1, $3, $2, 1000*$3/$2) | "sort -t: +0 -1 +4rn"}' countries.txt | awk 'BEGIN { FS = ":"

printf("%-15s %-10s %10s %7s %12s\n",

"CONTINENT", "COUNTRY", "POPULATION", "AREA", "POP. DEN.")}

{printf("%-15s %-10s %7d %10d %10.1£\n", $1, $2, $3, $4, $5)

}'

awk 'BEGIN { FS = "\t" }

{ printf("%s:%s:%d:%d:%.1f\n", $4, $1, $3, $2, 1000*$3/$2) | "sort -t: +0 -1 +4rn"}' countries.txt | awk 'BEGIN { FS = ":"

printf("%-15s %-10s %10s %7s %12s\n",

"CONTINENT", "COUNTRY", "POPULATION", "AREA", "POP. DEN.")}

{if ( $1 != prev) {

print ""

prev = $1

} else

$1 = ""

printf("%-15s %-10s %7d %10d %10.1f\n", $1, $2, $3, $4, $5)}'

awk 'BEGIN { FS = "\t"}

{ den = 1000*$3/$2; printf("%-15s:%12.8f:%s:%d:%d:%.1f\n",

$4, 1/den, $1, $3, $2, den) | "sort"}'  countries.txt

_____

vi prep3.txt

BEGIN { FS = "\t"}

pass == 1 {

area[$4] += $2

areatot += $2

pop[$4] += $3

poptot += $3

}

pass == 2 {

den = 1000*$3/$2

printf("%s:%s:%s:%f:%d:%f:%f:%d:%d\n",

$4, $1, $3, 100*$3/poptot, $2, 100*$2/areatot,

den, pop[$4], area[$4]) | "sort -t: +0 -1 +6rn"

}

awk -f prep3.txt pass=1 countries.txt pass=2 countries.txt

Labels: awk

posted by shantanu  # Friday, October 27, 2023

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