Shantanu's Blog

Database Consultant

November 18, 2023

 

awk Case Study - 10

Formats its input into lines that are at most 60 characters long

# fmt - format
# input: text
# output: text formatted into lines of <= 60 characters

awk '/./ { for (i = 1; i <= NF; i++) addword($i) }
/^$/ { printline(); print "" }
END { printline() }

function addword(w) {
    if (length(line) + length(w) > 60)
        printline()
        line = line " " w
    }
function printline() {
    if (length(line) > 0) {
        print substr(line, 2)
        line = ""
    }
}' long.txt  

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November 17, 2023

 

awk Case Study - 9

Cliche generator, which creates new cliches out of old ones. The input is a set of sentences like

# cat cliche.txt
A rolling stone:gathers no moss.
History:repeats itself.
He who lives by the sword:shall die by the sword.
A jack of all trades:is master of none.
Nature:abhors a vacuum.
Every man:has a price.
All's well that:ends well.

where a colon separates subject from predicate. Our cliche program combines a random subject with a random predicate; with luck it produces the occasional mildly amusing aphorism:

A rolling stone repeats itself.
History abhors a vacuum.
Nature repeats itself.
All's well that gathers no moss.
He who lives by the sword has a price.

# cliche - generate an endless stream of cliches
# input: lines of form subject:predicate
# output: lines of random subject and random predicate


awk 'BEGIN { FS = ":" }
{ x[NR] = $1; y[NR] = $2 }
END { for (;;) print x[randint(NR)], y[randint(NR)] }
function randint(n) {
    return int(n *rand()) + 1 
}' cliche.txt

Don't forget that this program is intentionally an infinite loop. 

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awk Case Study - 8

Isolate the words and aggregate the count for each word in an associative array. A word is a field without the punctuation marks like ? or ,

# wordfreq - print number of occurrences of each word 
# input: text 
# output: number-word pairs sorted by number 

awk '{
    gsub (/I [ ., : ; I ? ( ) { } ] /,  "" )
    for (i = 1; i <= NF; i++)
        count[$i]++
    }
END {
    for (w in count)
        print count[w], w | "sort -rn"
    }' capitals

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awk Case Study - 7

Print the names of the countries in Asia along with their populations and capitals:

# cat capitals
USSR Moscow
Canada Ottawa
China Beijing
USA Washington
Brazil Brasilia
India New Delhi
Mexico Mexico
France Paris
Japan Tokyo
Germany Bonn
England London

# cat countries
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

(make sure that the files are tab separated)

# awk 'BEGIN { FS = "\t"}
FILENAME == "capitals" {
    cap[$1] = $2
}
FILENAME == "countries" && $4 == "Asia" {
    print $1, $3, cap[$1]
}' capitals countries


USSR 275 Moscow
China 1032 Beijing
India 746 New Delhi
Japan 120 Tokyo

It would certainly be easier if we could just say something like

continent ~ /Asia/ { print $country, $population, $capital}

and have a program figure out where the fields are and how to put them together. This is how we would phrase this query in qawk

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awk Case Study - 6

The following program arith presents a sequence of addition problems like

7 + 9 = ?

After each problem, the user types an answer. If the answer is right, the user is praised and presented with another problem. If the answer is wrong, the program asks for the answer again. If the user provides no answer at all, the right answer is printed before the next problem is presented. The program is invoked with one of two command lines:

awk -f arith
awk -f arith n

If there is an argument after ari th on the command line, the argument is used to limit the maximum size of the numbers in each problem. After this argument has been read, ARGV [ 1 ] is reset to "-" so the program will be able to read the answers from the standard input. If no argument is specified, the maximum size will be 10.

BEGIN {
    maxnum = ARGC > 1 ? ARGV[1] : 10
    ARGV[1] = "-"
    srand()
    do {
        n1 = randint(maxnum)
        n2 = randint(maxnum)
        printf("%g + %g = ? ", n1, n2)
        while ((input = getline) > 0)
            if ($0 == n1 + n2) {
                print "Right!"
                break
            } else if ($0 == "") {
                print n1 + n2
                break
            } else
                printf("wrong, try again: ")
    } while (input > 0)
}
function randint(n) {
return int(rand()*n)+1
 }

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awk Case Study - 5

Mail-merge using AWK


# cat letter.text
Subject: Demographic Information About #1
From: AWK Demographics, Inc.
In response to your request for information about #1, our latest researchas revealed that its population is #2 million people and its area is #3 million square miles. This gives #1 a population density of #4 people per square mile.


# echo "Canada:25:3.852:6.5" | awk 'BEGIN {
    FS = ":"
    while (getline < "letter.text" > 0)
        form[++n] = $0
    } {
    for (i = 1; i <= n; i++) {
        temp = form[i]
        for (j = 1; j <= NF; j++)
            gsub("#" j, $j, temp)
            print temp
        }
}'

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