Editing AWK (section)

=== Sum last word ===

<syntaxhighlight lang="awk">
{ s += $NF }
END { print s + 0 }
</syntaxhighlight>

<code>s</code> is incremented by the numeric value of <code>$NF</code>, which is the last word on the line as defined by AWK's field separator (by default, white-space). <code>NF</code> is the number of fields in the current line, e.g. 4. Since <code>$4</code> is the value of the fourth field, <code>$NF</code> is the value of the last field in the line regardless of how many fields this line has, or whether it has more or fewer fields than surrounding lines. <code>$</code> is actually a unary operator with the highest [[operator precedence]]. (If the line has no fields, then <code>NF</code> is 0, <code>$0</code> is the whole line, which in this case is empty apart from possible white-space, and so has the numeric value 0.)

At the end of the input, the <code>END</code> pattern matches, so <code>s</code> is printed. However, since there may have been no lines of input at all, in which case no value has ever been assigned to <code>s</code>, <code>s</code> will be an empty string by default. Adding zero to a variable is an AWK idiom for coercing it from a string to a numeric value. This results from AWK's arithmetic operators, like addition, [[Type conversion|implicitly casting]] their operands to numbers before computation as required. (Similarly, concatenating a variable with an empty string coerces from a number to a string, e.g., <code>s ""</code>. Note, there is no operator to concatenate strings, they are just placed adjacently.) On an empty input, the coercion in <code>{ print s + 0 }</code> causes the program to print <code>0</code>, whereas with just the action <code>{ print s }</code>, an empty line would be printed.