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(gawk.info)Truth Values

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True and False in `awk'
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   Many programming languages have a special representation for the
concepts of "true" and "false."  Such languages usually use the special
constants `true' and `false', or perhaps their uppercase equivalents.
However, `awk' is different.  It borrows a very simple concept of true
and false from C.  In `awk', any nonzero numeric value _or_ any
non-empty string value is true.  Any other value (zero or the null
string `""') is false.  The following program prints `A strange truth
value' three times:

     BEGIN {
        if (3.1415927)
            print "A strange truth value"
        if ("Four Score And Seven Years Ago")
            print "A strange truth value"
        if (j = 57)
            print "A strange truth value"
     }

   There is a surprising consequence of the "nonzero or non-null" rule:
the string constant `"0"' is actually true, because it is non-null.
(d.c.)