CODEWITHSUNDEEP
linuxbashshellawk
FNF
FNF

Reputation: 47

AWK script input

#!/bin/bash -f

awk '

BEGIN {
    print "type a number";
}
{
    printf "The square of %d is %d\n", $1, $1*$1;
    #print "The square of ", $1, " is ", $1*$1;
    print "type another number\n";
}
END {
    print "Done"
}'

Can anyone explain how this program takes input? I tried searching on the web but in vain. Grateful for any explanation given. Thanks.

Upvotes: 1

Views: 721

Answers (1)

Quasímodo
Quasímodo

Reputation: 4004

The program takes input from stdin. So, after making it executable with chmod +x scriptname, you can either start it with ./scriptname and answer to each prompt, or redirect a file's content to stdin. For example, suppose this is numbers.txt:

4
7
1

Then execute the script this way:

$ ./scriptname < numbers.txt
type a number
The square of 4 is 16
type another number

The square of 7 is 49
type another number

The square of 1 is 1
type another number

Done

Why does that awk script read standard input? According to awk POSIX specification, section STDIN:

The standard input shall be used only if no file operands are specified, or if a file operand is '-', or if a progfile option-argument is '-';

Notice that awk was provided no file operand, so stdin is used.

Upvotes: 2

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