Editing field reference

== The field reference operator == The [[dollar]] symbol acts as a unary *field reference operator* and is followed by a number or expression that gives a [[field]] number within the [[current record]]: {{{ { print $3 } # output field number three }}} === Field numbers are not limited to single digits === Unlike the positional parameters in the Unix shell, [[field]] numbers are not limited to single digits: {{{ { print $123 } # output field number 123 }}} ==== Using a variable name to specify the field number ==== It is possible to use to use a [[variable name]] after the dollar sign to specify the field number: {{{ { myfield = 4 print $myfield # output field number 4 } }}} === Using an expression to specify the field number === It is also possible to use an [[expression]] after the dollar sign to specify the field number. Note that [[parentheses]] are used around the [[expression]], to ensure [[evaluation]] of the [[expression]] takes [[precedence]] over the field reference operator: {{{ print $(3 + 2) # output field number 5 # The parentheses above are important. # Without parentheses, we would get a value 2 more than field 3 }}} === Referencing a non existent field will produce an empty string === Attempting to reference a non existing field produces an [[empty]] string. === Referencing field zero gives the entire record === If a value of [[zero]] is given as the [[argument]] following the dollar symbol, then the entire record is referenced: {{{ { print $0 } # output the entire record }}} === Field numbers must not be negative === It is not permissible to use negative field numbers. Attempting to reference a negative field number will cause [[undefined behaviour]], or a [[fatal error]] will occur. === Assignment to referenced field === It is possible to change the contents of a [[field]] in the current [[record]] by making an [[assign]]ment to the referenced field: {{{ { $2 = 23 } # Change field two to a value of 23 }}}

Summary:

This change is a minor edit.

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