Editing dollarint

A [[dollar]] sign and followed by an [[integer]] are used to refer to [[field]]s within the current [[record]]: {{{ awk { print $3 } # output field number three }}} Though you might consider $3 as a variable, it's not exactly true, in fact $ is the field reference operator and 3 is just a number that tells awk you want to reference the third field. They behave a bit like an array ie where with an array you would write fields[1] in awk you write $1 If you know C it behaves like the * on a pointer. == Field numbers are not limited to single digits == Unlike the positional parameters in the Unix shell, fields are not limited to single digits: {{{ awk { print $123 } # output field number 123 }}} == Field numbers do not need to be constant == The field number after the $ does not need to be a [[constant]]. === 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: {{{ awk { 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]] before the field number: {{{ awk print $(3 + 2) # output field number 5 # The parentheses above are important. # Without parentheses, we would get a value 2 more than field 3 }}} == A dollar sign followed by a zero references the entire record == A [[dollar]] sign and followed by a zero references the entire record: {{{ awk { print $0 } # output the entire record }}} == Referencing a non existent field == Reference a non existing [[field]] will produce an [[empty string]]. === Field numbers must be positive === 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 dollarint variables == It is possible to change the contents of a [[field]] in the current [[record]] by making an [[assign]]ment to the dollarint [[special variable]]: {{{ awk { $2 = 23 } # Change field two to a value of 23 }}} == See also == * [[NF|Number of fields]]

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This change is a minor edit.

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